bfor those who like photography -a simple book asics of photography

2 Basics of Photography

Title Page No.

What is a Camera and Types of Cameras? 04

Fundamentals of Lenses and Types of Lenses 16

Pixel Count and and Print Size 34

File Formats 46

Exposure Modes, Controls and Meters 59

Metering 74

Histogram and highlight warning 89

White Balance 97

Some optical issue, Defects and Perspective 104

Depth of Field 116

Flash (Part I) 127

Flash (Part II) 139

Elements of Composition (Part I) 150

Elements of Composition (Part II) 159

Basics of Photography 3

Learning Basics of Photography

Smart Photography has been continually receiving requests to start a basic course for beginners. With this in mind, we have asked a very knowledgeable photographer from Hyderabad, Andhra Pradesh, to take over writing these articles. We have also requested him to be as jargon-free as it is possible, so that newcomers to photography feel comfortable to pursue the hobby.

The author, Ashok Kandimalla has been in the photographic field for over three decades and has extensive experience in both film and digital photography. Being an electronics engineer by profession and a photographer, he possesses a unique and deep insight into the technical aspects of digital photography and equipment. He has published several articles on photography and some of his writings have also been published in the well-known international magazine Popular Photography.

An avid collector of photographic books and vintage cameras, Ashok has a keen interest in the history of photography and a passion for sharing his knowledge on photography through teaching and writing. He is presently working as a Management and Engineering consultant. You can see his work at http://www.flickr.com/photos/ashok_kandimalla. He can be reached at [email protected]


What is a Camera andTypes of Cameras?

Have you been waiting to start photography but putting it off due to the confusion and jargon that confronts you? The series of articles to follow will explain the basics to overcome just that.

To start with - what is a camera? Simply put, a camera is a light tight box (body), which holds a light sensitive recording medium (film or sensor in the case of digital cameras) and optics (lens) to form the image on the medium. Since film cameras are rapidly being superseded by digital cameras we will confine our discussion only to these.

The body also houses a mechanism (shutter), which sets the duration for which light is allowed to act on the sensor. Since you need to see what youll be photographing, there is also a component (viewfinder) to show what you are going to photograph.


LETS Look aT THESE CoMPoNENTS IN MorE DETaIL.Body: This houses the components mentioned above plus a few more, in a light-tight chamber. The lens, which is attached to the body sees a certain area that is indicated in the viewfinder. Once the shutter release button (commonly and erroneously called click) is pressed an image is captured.

Flash Memory Cards

In the case of film cameras, the image is stored on a film. It is later retrieved by developing the film. In digital cameras there is no film; instead there is a component known as flash memory card on which the image captured by the sensor is transferred to. But here is a small

problem. The sensor can record the image instantly but the flash memory card cannot it takes a while to do that. And unless the image from the flash memory card is transferred, you cannot place another image on the sensor. So to circumvent this problem, the image is sent to a temporary storage device known as the buffer. The buffer can copy the images almost as soon as the sensor can capture them. It then transfers the images to the memory card at the speed at which the card is capable of receiving the images. The memory card can be taken out of the camera whenever one desires (it is not necessary to completely fill the card before taking it out of the camera) and the images on it can be transferred to a computer for permanent storage or printing. The camera body contains a slot to hold the flash card.

The lens needs to be correctly focused for the image to be sharp. For this purpose the body houses an autofocus mechanism which detects an out of focus image and moves the lens or parts of the lens to bring the image into focus. In addition the body contains the exposure meter (more of it later).


Lens: The lens, along with the sensor (or even more than the sensor) has a major influence on the picture quality and hence is the most important part of the camera. A lens is made up of several optical elements though only the front-most one can be seen. The lens in essence is the eye of the camera and is responsible for forming the image on the sensor.

Normal Lens

Wide-angle Lens Telephoto LensZoom Lens

An important characteristic of a lens you need to be concerned about is the focal length which determines the magnification of the image. The longer the focal length the higher will be the magnification. Technically speaking, focal length is described as the distance between the sensor and the rear nodal point of the lens (more about it in some later article). Lenses with long focal length are called telephoto lenses and are useful for photographing distant subjects like birds, wildlife and sports. Short focal length lenses are called wide-angle lenses and as the name implies, cover a large area. These are meant for photographing sceneries, interiors of buildings, etc. In between these two are normal


lenses which produce an image close to what a human eye sees. Lenses having single focal length are also known as Prime lenses.

Fast Lens

Fast LensA lens with greater light gathering power is known as a fast lens and is identified by f/nos like 1.2, 1.4, 1.8. The lens shown on the left is considered to be extremely fast at f/0.95

Slow LensA lens with lesser light gathering power is known as a slow lens. Eg. f/4, f/5.6.

Lenses whose focal length can be continuously varied are called zoom lenses. You can have a wide-angle zoom (focal lengths stay lower than for normal lens) or wide-to-telephoto zoom (focal lengths vary from wide-angle to telephoto) or telephoto zoom (focal lengths stay on the telephoto side only). With a zoom lens (which is the most popular type) you can get, for example, both telephoto and wide angle effects.

The other important characteristic of a lens is the speed which determines the light gathering capacity of the lens. Higher speed lenses can take pictures in lower light. They also allow faster shutter speeds to be used for the same light.

Every lens has what is called an aperture. This controls the amount of the light that will pass through the lens and subsequently fall on the sensor. The size of the aperture (hole) can be varied. Just like the pupil in our eyes, the opening can be made small in bright light and made larger in low light. Small openings are called narrow apertures and larger openings are called wide apertures. Wider apertures provide less depth-of-field while narrower apertures provide greater DOF (more of it later).


The Sensor: This is placed in the camera body, where the light rays from the lens focus. The sensor is a silicon chip manufactured with light gathering elements. These elements produce an electric charge proportional to the intensity of the light falling on the element. This means more the light, the greater will be the electrical energy. The circuitry on-board the camera measures this energy and hence knows the intensity of light at each photo element. By putting together measurements taken for each element, the on-board computer will be able to construct the entire image which will have as many dots as there are elements. Each of these dots is called a Pixel which is the short form for picture element.

The two most important parameters of the sensor are the number of pixels and size of


the pixels. The number of pixels are normally specified as Mega (or millions of ) pixels. So how many pixels do you need in your camera? That depends on the size of prints you want to make. Typically a 8 megapixel sensor can produce a quality 8x10-inch print at about 300 dots per inch (or dpi). The significance of 300 is that a human eye can resolve only about 300 dpi. The second parameter the size of the pixel, is less talked about but equally important. This has a strong bearing on the quality of the image. Larger pixels have better light gathering capability and hence can capture cleaner (noise free) images. This means that for the same number of pixels a larger sensor which naturally allows for larger pixels produces better images. The downside is the higher cost of the larger sensor.

Viewfinder: This shows you what the lens is seeing and hence what is going to get recorded on the sensor. Note that the viewfinder may not always show a 100-percent view as seen by the lens. The viewfinder can be implemented in several ways as we will see later.

Liquid Crystal Display (LCD) Monitor: An LCD monitor is at the back of the camera. In compact digital cameras, this can be used as a through the lens (TTL) viewfinder to preview the picture before it is taken. Some newer digital SLRs also provide this feature and it is known as Live View. It can also be used to review (play back) the image after it has been captured.


Shutter: The shutter first allows light to fall on the sensor and then cuts it off to record a moment in time. To take pictures, first make sure that what you want to photograph is shown in the viewfinder. Now, gently press the shutter release button. This causes the shutter to open for a specified time and then close, capturing the image. The time duration for which the shutter is open is very short, normally a fraction of a second.

Exposure Meter: This measures the brightness of the light and determines the correct amount of light (called exposure) that needs to fall on the sensor to produce an image that is properly exposed neither too dark, nor too light. The exposure meter tells us what shutter speed and aperture to use to achieve the desired exposure. The meter also controls the shutter speed and aperture to achieve this.

In practice, several combinations of shutter speed and aperture can achieve the same exposure. For example, a slow shutter speed combined with a narrow aperture gives same exposure as a fast shutter speed with a wide aperture. This is called reciprocity. So which combination should you choose? Let us examine this in some more detail.

Do you want to stop a moving car in its tracks? Choose a fast shutter speed. Fast shutter speeds allow less light and to compensate we need wider apertures. (Wider apertures produce less depth of field (zone of sharpness) than narrow apertures something that well talk about in greater detail in the following chapters). You may also need a faster lens.

Do you want to photograph scenery with a tree in the front, plus a mountain in the back and want both to be tack sharp? Choose a narrow aperture. This will naturally allow less light which needs to be compensated by using a slow shutter speed. You will need a camera support (like a tripod) with slow shutter speeds as otherwise the picture will be blurred due to camera movement caused by shaking of hands.

Flash: Often included in the body is a flashgun. This is an artificial source of light that is useful when taking photographs in low light. While flash is handy just remember that it is effective only for short distances. In other words dont try to photograph the Taj Mahal in the night using flash!


Just one point - the viewfinder, LCD monitor, flash and lens are visible externally on a camera. However, auto focus mechanism, exposure meter, shutter, sensor etc. are not visible externally. Now that you know the basic components of a camera, let us look at the different types or classes of cameras that are popular today.

In the past cameras were classified depending on the size of the film used. Thus, we had 35mm or medium format or large format cameras. Another way in the past was to classify based on the how the viewfinder was implemented. This resulted in cameras called coupled rangefinders, single lens reflexes (SLR), twin lens reflexes (TLRs, which used separate lenses for viewing and picture taking), etc. Presently these classifications are not very convenient as some of the types have simply vanished or the technology has changed rendering such classifications rather irrelevant.

To keep the discussion state of the art, we will classify the cameras as four types: Point and Shoot, Bridge (Prosumer) Camera, Digital Single Lens Reflex (D-SLR) and Compact System Cameras (CSC). Let us see what their characteristics are:

Point and Shoot (P&S): These are compact cameras offering fully automatic focus and exposure operation. The operation is very simple you need to just point and press the shutter release; hence the name point and shoot.

P & S

Some P&S cameras also have a separate optical viewfinder which is useful when photographing in bright light as an LCD monitor can be difficult to view under these circumstances. However, this viewfinder can cause parallax error when photographing close-by subjects. (In other words, what the viewfinder sees, may not be seen by the lens).


Bridge (Prosumer) Camera: This type is characterized by having a fixed (non-interchangeable) lens with a large zoom range (that is from wide-angle to powerful telephoto). They are equipped with an Electronic View Finder (EVF) which is a small LCD screen with a suitable eye piece. The EVF allows more convenient eye level viewing. The bridge cameras also typically have better flash and exposure control.

Consider these as more advanced P&S type, the primary differences beingbetter control, eye level EVF viewing and a fixed (non-interchangeable) lens with a large zoom range.

The name comes from the fact that they fall in between a P&S and an D-SLR in terms of sophistication, control, versatility and of course cost. Thus, they can be considered as a bridge for crossing the gap between a P&S and a D-SLR. They are also at times called Prosumer camerassomething in between professional and consumer cameras.


Single Lens reflex (SLr):

SLr DIgraMPentaprism

Mirror up

Mirror down

Light rays

Sensor/Film

Shutter

Viewfinder

T h e v iew f i nder of an SLR has a complex optical set-up to show the image. A mirror which is in front of the sensor and behind the lens reflects (hence the name reflex) the light to a 5-sided prism (known as pentaprism) which in turn directs the light to the viewfinder. The mirror swings out of the path when the shutter release is pressed, allowing the image to be captured by the sensor. After this, the mirror comes back to its original position restoring the viewfinder image.

The word single in SLR owes its origin to the fact that the same (single) lens is used for picture taking and viewing. Consequently, the viewfinder image is free from parallax. This is one of the main differences between an SLR and the other two types.

Digital SLRs are often called D-SLRs to distinguish them from film SLRs which are out of or in limited production these days.

Like P&S and bridge cameras, D-SLRs have an LCD monitor. This allows review of


the image you have taken. However, the preview feature is a bit more complicated in a D-SLR. This is due to the fact that the mirror blocks the light path to the sensor. This has been overcome in the newer D-SLRs with a facility called Live View.

When Live View is activated, the mirror swings out of the way. The shutter is also opened and this allows you to preview the image. This has certain advantages in close-up photography. Of course during the time Live View is on, the optical path is blocked and you will not be able to see anything through the optical viewfinder.

Compact System Camera (CSC): These are also called mirrorless cameras. Compared to the complexity of a DSLR, a CSC is very simple in construction. There is no mirror or prism and the light simply passes through the lens and falls on the sensor. There is no optical viewfinder. The image that is recorded by the sensor is shown on the LCD monitor on the back of the camera and this will serve as a viewfinder. Most high end CSCs, however, come with an EVF built in apart from the usual LCD monitor. Alternatively, you can look at a CSC as a P&S camera with interchangeable lenses and a bigger sensor.

D-SLRs and CSCs support interchangeable lenses. This is a facility which allows a lens to be removed and attached with ease. Because of this, a wide variety of lenses (from super wide to super telephoto), each best suited for an application can be used.

D-SLRs and CSCs provide the best image quality due to the large sensors that have larger pixels and also high pixel count. D-SLRs also have more sophisticated metering systems and complete manual override for every automatic function thus allowing total control for creative photography. They also have a versatile flash system and a very large range of accessories.

So which camera type is best for you? Here is a table which lists the pros and cons of all the three types to help you make a decision.


Camera Type Pros Cons

Point and Shoot:Best for family pics, holiday, travel and small size prints

Bridge Camera:Best when there is a need for large zoom range, larger prints, but do not want to be bothered by the bulk and cost of a D-SLR.

D-SLR:For ultimate picture quality and versatility if you do not mind the bulk and cost (and your spouses complaints!). It is also the right tool if you are serious or want to make a living out of photography.

CSC: High picture quality close to or matching that of a DSLR.

Easy to useCompactLow costNice for candid photography

All in - one cameras that have large range zoom lenses.Eye level TTL viewing through EVF

System cameras offering a large range of accessories and lenses.Vastly superior flash system.Best picture quality for large prints.Sharp, crisp viewfinder image with no lag that is inherent in LCDs.Excellent control over all parameters aids creative techniques.Very fast autofocus.Perhaps the best of both worlds compact size, interchangeable lenses and high picture quality System cameras though the breadth and depth of offerings do not match that of DSLRs. This is however, changing fast. Quiet operation due to lack of mirrorIdeal for travel, candid and street photography.

Limited control over final image.Small zoom range of lens restricts usage for many applications like wildlife.Small, weak flash.Inferior picture quality compared to a D-SLR due to smaller sensor.

Large range zooms can compromise on picture quality.Non-interchangeable lenses limit versatility.Larger size compared to P&S.Limited range of accessories and inferior picture quality compared to a D-SLR

Large size and weight.High cost.Conspicuous, so not good for candid photography.Complex and sometimes difficult to use.

Lacks optical viewfinders Many low end CSCs dont even have an EVF forcing you to use only the LCD monitor.


Fundamentals of Lenses and Types of Lenses

The lens is the eye of the camera and is responsible for forming the image on the sensor. To a great extent the quality of the picture that is recorded depends on the quality of the lens. Consequently, the lens is the most important part of the camera.

Lens Design: When a designer designs a lens he will have to deal with a set of conflicting requirements in the form of weight, cost, size, the amount of distortion he can allow, etc. As is the case with any design he will make a trade-off between various factors. As such, finding a perfect lens is as easy as finding a perfect human!

Important attributes of a lens: There are two important attributes to a photographic lens. One is the focal length and the other is the speed.

Focal Length: This determines the size of the image that is formed on the sensor. A lens with longer focal length will form an image that is larger compared to a lens with shorter focal length at the same subject-to-lens distance. This also means that longer focal length lenses see a smaller area than short focal length lenses.

Focal length is measured in millimeters (abbreviated as mm). This is the distance between the lens and the plane on which the image is sharply formed, when the lens is focused at infinity.

Focal length

Sensor

Ligh

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ing

from

infin

ity

Focal LengthIn this diagram we have symbolically shown only one element. However, a photographic lens is made up of multiple elements. There will be at least four elements in a photographic lens and some complex designs can have more than 20 elements. When you look


at a photographic lens from the front of the camera, you are looking only at the front element. Multiple elements are needed to correct several optical defects that are inherent with a single element design. Higher number of elements is also needed in complex designs like zoom lenses.

18mm 35mm

50mm 70mm

100mm 140mm

200mm 300mm

These photos were all taken from the same spot but with different focal lengths to show the effect of focal length on the image size

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Contrary to conventional thinking, you cannot say that you will get a telephoto or a wide-angle effect (we will define these terms shortly) at a particular focal length as that depends on the Angle of View (AOV). The AOV depends on focal length as well as the size of the sensor (also called format). The effect of AOV is best explained with an example. See the diagram which shows what the AOV means. A 35mm camera has a format of 24x36mm. A 50mm lens on such a camera has an AOV of 46 degrees. Now consider that same lens mounted on a D-SLR which has an APS-C size sensor. Here the frame is approx.18x24 mm and the diagonal is approximately 1.5 times less than that of a normal 35mm frame. Hence the AOV now becomes 1.5 times less or 32 degrees, which is same as that of a 75mm lens on a 35mm camera. Conversely to get an AOV of 46 degrees on such a D-SLR you need to use a lens of focal length of approximately 33mm.

The effect is as if you cut a part (crop) which is 18x24mm in size out of the 35mm format. Thus you are now seeing a smaller part of 24x36mm which has the same effect as decreasing the angle of view by 1.5 times. This is popularly called the cropping factor and has the apparent effect of virtually increasing the focal length. However the focal length does not increase and the magnification of the image does not change. In essence you are taking a smaller area and enlarging it more. It is as simple as that!

This in fact is nothing new nor is just confined to cropping. It holds equally good when formats larger than 35mm are used. Photographers who use medium format cameras know that an 80mm lens on a medium format camera has an angle of view close to that of


a 50mm lens on a 35mm camera. Digital cameras have sensors of various sizes. Since many of us are used to define classes of lenses as used on a 35mm camera (for e.g. we know that a 28mm lens is a wide-angle) manufacturers mention this figure in the literature. Some manufacturers have started to mark lenses with equivalent 35mm focal lengths while at the same time not explicitly declaring so. This is not technically correct. This practice is fortunately confined to consumer Point and Shoots and bridge cameras and not D-SLRs. Table 1 gives the conversion factors for sensors of several sizes.

Table 1

Sensor Size Used By Approximate Conversion Factor with reference to 35mm (Multiply focal length or divide the angle

of view by)

Several sizes, from Point and shoots Can go up to 65mm diagonal to and bridge cameras or even more11mm (approximately) Micro Four Thirds System (MFT) Olympus and Panasonic 2.00 APS-C All Canon D-SLRs except EOS 1D 1.60 and 1Ds series

DX All Nikon D-SLRs except D3, D700, D3X. 1.50 Sony / Minolta and Pentax D-SLRs

APS-H Canon EOS 1D series, Leica M8 1.30

Full Frame (FX) or Nikon D3, D3X, D700; 1.0035mm film Canon EOS-1Ds series

Film 6x4.5 cm Pentax, Mamiya, Bronica, Hasselblad 0.58

Film 6x6 cm Pentax, Mamiya, Bronica, Hasselblad 0.51


Most of the super zoom equipped bridge digital cameras have very small sensors and thus need only a short focal length to get a great telephoto effect. For example, if you study the specification of a digital bridge camera that claims to have a super telephoto of 500mm (equivalent focal length for 35mm camera), you will find that the actual focal length is just about 90mm. A lens of this focal length on a 35mm camera would qualify as a short telephoto and on a medium format as a normal lens!

To conclude, we cannot classify a lens is a tele or something else just by looking at the focal length alone. The format also needs to be taken into account.

The second important characteristic of lenses is the speed.

Lens SpeedContrary to what the name indicates it does not have anything to do with the speed of the subject that can be photographed. Speed is an indication of the light gathering capacity of the lens and is referred to as the f number. It is denoted as f/. Mathematically it is (sorry cant avoid mathematics!) focal length divided by the optical diameter of the lens. Think of the lens as a light gathering funnel. Larger the diameter of the funnel, more will be the area for collecting the light and hence the ability to take picture in lower light. Faster the lens, larger will be the diameter and lower will be the f number. Since you need to have a mechanism to control the light passing through the lens, every lens has a diaphragm (sometimes called Iris) similar to the iris of the human eye. It has a set of blades which create an opening commonly known as the Aperture. The diaphragm can be closed when the light is bright (that is, aperture is made smaller). Conversely it can be opened when the light is less (aperture is made larger). The size of the aperture is controlled with the help of a dial or ring. In certain automatic exposure modes, the camera itself can select a suitable aperture. The opening is calibrated so that by turning the ring light passing through can be increased in steps. Each step is called a stop. The stops are calibrated as follows: 1.0 1.4 2.0 2.8 4.0 5.6 8.0 11 16 22 32 45 64

Each succeeding stop allows one half of light that is allowed by the previous stop.


Thus a stop of f/11 allows double the light of f/16 and half the light of f/8. So, larger f numbers have smaller openings and smaller f numbers, larger openings.

Those of you who are math oriented should have noticed the stops are in fact approximate multiples of 1.4 which is the square root of 2. That is because each stop doubles or halves the area of the aperture opening.

You might find reference to what is called automatic diaphragms is some old literature. This has nothing to do with automatic exposure. We have seen that SLR cameras allow viewing through the lens. If a small aperture (that is large f/ number) is chosen and if the diaphragm blades are closed to this value, then the amount of light that is passing through the lens reduces, making the image in the viewfinder very dim. This makes viewing and focusing difficult. To overcome this, the diaphragm is kept fully open regardless of the aperture you have chosen or the camera has chosen. When you release the shutter, the mirror swings up and at this point of time the diaphragm is closed (also called stopped down) to the aperture value that has been chosen. Then the shutter opens and closes, the diaphragm opens fully and then the mirror falls back to its original position restoring the image. Since, once set, the diaphragm blades open and stop down without any intervention these are called automatic diaphragms. Today virtually all D-SLR lenses are fully automatic in this sense. However, you need to be aware of this since at times it is necessary to stop down the diaphragm to the picture taking value to see the effect of depth of field. We will talk about that later.

Fast lenses have two advantages. They allow you to photograph in lower light levels for the same shutter speed or use a faster shutter speed for the same light. Hence fast lenses are very useful for low light and action (sports, wildlife, etc.) photography. As with everything in life there is no free lunch. Fast lenses are very heavy, especially at long focal lengths. The table below, which shows the weight of four 300mm lenses from the same manufacturer but with different speeds, illustrates this very well.


Speed of lens Weight in grams approx. US Pricef/5.6 505 $500f/4.0 1,440 $1,200f/2.8 2,870 $4,500f/2.0 7,545 (Discontinued) $29,000

You can see that an increase in one stop in speed has a drastic effect on weight. Price too increases rapidly with the f/2.8 version costing more than four times the f/4.0 version. There are a few other aspects that you need to know to complete the picture. These are the focusing mechanism, lens mount, filter threads and image stabilization.

Focusing Mechanism: The lens forms the image at the focal plane. The focal plane denotes where the sensor is placed. Since the subjects we photograph are at varying distances, a lens needs to be focused on the required subject in the frame. This requires that the elements within the lens need to be moved away from the focal plane when photographing near objects and towards the focal plane when photographing distant subjects. This is normally done by the focusing mechanism called helical.

Focusing can be done manually by turning a ring called the focusing ring on the lens and checking the sharpness in the viewfinder in the case of D-SLRs.

In the case of autofocus lenses, the mechanism that detects the out of focus state is within the camera body. The mechanism then drives the lens in one of the following two ways:

(a) There is a motor in the camera body which focuses the lens through a mechanical coupling; or (b) Using electronic contacts, the body signals the motor which is inside the lens and this motor does the needful. When the correct focus is detected by the body, the driving stops.

Lens showing the AF contact points on the lens mount

Lens Mount: One thing you need to know is that all D-SLRs that support interchangeable lenses have what is called a mount. This is a system of mechanical and electronic linkages that ensure proper interface between the lens and the camera body. This mount is


proprietary to each brand with the sole exception of the Four Thirds System. You cannot for example, use a Nikon lens on a Canon camera body and vice versa. However, lenses made for Micro Four Thirds (MFT) System are usable on all MFT D-SLRs.

There are also several independent lens manufactures who produce lenses in different camera mounts. However, the mount cannot be changed after the purchase of the lens though such a system (called T mount) was once available. You need to bear this in mind as once you build a system around a brand it is difficult to change it without a big expense as you need to change all the lenses and most of the accessories to the newer brand.

Filter Threads: The front of the lens has a thread which can be used for mounting filters. Filters are optically flat pieces of glass which are usually kept in a circular frame. This frame can be screwed on to the lens. While filters have several uses, for the time being just remember that you should keep a suitable (either Skylight or UV) filter to protect the front element of the lens from dust, fingerprints, etc. and to prevent scratches. Since all lenses are not of the same diameter, you need to buy a filter of the right size that fits your lens. So how do you know which diameter to buy? Simple. This is normally mentioned on the back of your lens cap as a number followed by mm (millimeters) followed by the symbol . Thus, if it is mentioned 52mm, you need to buy a filter of 52mm diameter.

Image Stabilization (IS): We have seen earlier that handshake can adversely affect the sharpness of a picture. While using a tripod is the best way to eliminate camera movement during exposure, there is a technology which will result in sharper hand-held images when used correctly. Canon calls this as Image Stabilization (IS); Nikon labels it as Vibration Reduction (VR); and Panasonic refers to it as Mega Optical Image Stabilizer (MOIS). Here, the shaking of hands is detected by gyroscopes within the lens and a group

of elements are moved to counteract this. With this you can use 2 to 3 steps of slower shutter speeds than what is permitted without this feature. Thus, if a shutter speed of 1/500sec is warranted to hand-hold a particular focal length lens, you can go to 1/125sec or even 1/60sec and still get a sharp picture. This technology


is proving to be very popular with a number of lenses now being equipped with this feature. However, for very slow shutter speeds you still need to use a tripod. Also, note that a moving subject cannot be stopped with image stabilization. For that you need a fast shutter speed which necessitates the use of a fast lens (or use an action-freezing electronic flash). Note that image stabilization is a feature that is not visible from the outside. However, all lenses with this feature have a switch to activate or deactivate it. This can help you identify lenses with IS/VR/MOIS or an equivalent feature.

DIFFErENT TyPES oF LENSESPreviously, we have seen the important characteristics of lenses. Based on these, lenses are classified as Normal, Wide-angle, Telephoto and Zoom lenses.

Normal: A normal lens is the one which has a focal length equal to the diagonal of the frame. Generally these are also the fastest lenses and hence are best suited for low light photography. They provide a view that is close to that of a human eye. Example, a 50mm lens in the 35mm format.

Telephoto lenses: Lenses with long focal length are called telephoto lenses or teles for short. Due to their large focal length they provide high magnification and narrow angle-of-view. They find maximum application in wildlife and sports. They have the effect of compressing that is the distance between near and far objects looks less than what it is. For a D-SLR, typical telephoto lenses are available as 80mm, 135mm, 200mm, 300mm, 400mm etc.

Since magnification is high, there is tendency for any camera movement induced by handshake to show up very easily. You need to use a shutter speed of at least 1/equivalent focal length. That is, if you want to hand-hold a 200mm lens on a D-SLR (with APS-C size sensor, 1.5x crop factor) you need to use a shutter speed of at least 1/300 (not 1/200) of a second. If light is not sufficient for such a shutter speed then it is best to reach out for your three legged friend - the tripod, unless your lens has the image stabilization feature. Remember, in most cases fuzzy pictures taken with telephoto lenses are due to handshake problem.


Wide-angle lenses: These are opposite-end counterparts of telephoto lenses and have a wide angle of view. (Eg: 35mm, 28mm, 24mm, 20mm etc for a D-SLR). They also decompress or expand the relative distance between the objects. Wide-angle lenses can cause some peculiar problems which we shall cover when we discuss about perspective. In any case remember these are best for landscapes, interiors, etc. They should not be used for certain applications like tight portraits where the short focal lengths will force you to go very close to the subject thereby exaggerating some features like the nose. This will result in not-so-flattering portraits.

From the discussion we had on the focal length previously, you can see that the short focal length of a wide-angle lens would cause the rear end of the lens to be very close to the film/sensor. This would interfere with the movement of the mirror in an SLR. To resolve this problem, ultra-wide-angle lenses are designed on the principle of retro-focus. This allows such lenses to be produced with sufficient physical length, but at the same time keeping the focal length short. This prevents the lens from hitting the mirror.

Prime Lenses: Lenses whose focal length cannot be changed are called prime lenses. You can have prime telephotos and wide-angles for example. Prime lenses are also known as Block lenses.

Zoom Lenses: A class of lenses called zoom lenses is now very popular. Almost all cameras that do not allow interchangeable lenses have a zoom lens. A zoom lens, in simple terms, allows the user to change the focal length without actually changing the lens! In short, a zoom lens is the one that has multiple focal lengths built into it.

For example, you can vary the focal length from a wide-angle to telephoto and anything in-between without actually replacing the lens. No doubt this is very handy and the popularity of zoom lenses attests to this. Zoom lenses are available with different focal length ranges some covering ultra-wide-angle to moderate wide-angle and some covering short/medium telephoto to super telephoto. The


most popular ones for day-to-day use are those that cover from moderate wide-angle to medium telephoto.

The number you get by dividing the longer focal length of a zoom lens by the shorter focal length is called the zoom ratio. Thus if you have an 18 to 72mm zoom lens, the zoom ratio is four (4). You can have very large zoom ratios (in excess of 20). Generally such high ratios mean some compromise in quality, though there are exceptions.

As we have seen in the discussion on bridge cameras, it is now possible to incorporate a zoom lens with a huge zoom ratio (as high as 20) in a relatively small digital camera. Such a thing would not be possible with a 35mm camera. The reason for this is the relatively small sensor used in such digital cameras. Thus we can have a 5 to 90mm focal length on a bridge camera which corresponds to a 28 to 500mm lens on a 35mm camera! A 28-500mm lens on a 35mm format camera would be huge in size and technically a challenge to design and manufacture. In fact no such lens has ever been made, at least as yet!

During the early years of introduction of zooms, it was said that zooms lacked the image quality of prime lenses. However, this is no longer true for high quality zooms. Only at extreme ends of wide-angle or telephoto range are the prime lenses being used now. Another area where primes are used is when low distortion or high light-gathering power (fast lens) is required. For the rest of the cases, zooms are more popular and that too by a wide margin.

Zoom lenses are supposed to hold focus when the focal length is changed. Such lenses are called parfocal zooms. However, such lenses are difficult to design and costly to produce. Most of the zoom lenses produced today are varifocal type where the focus changes when you zoom. Hence, you need to focus after you zoom to the required framing. This is something you need to remember when you are using zoom lenses.


Pic showing various parts on a zoom lens

Filter threads Focusing Ring

Zoom Ring ApertureRing Lens

Mount

So, how do you change the focal length in a zoom lens? Zoom lenses in D-SLRs normally have a ring on the lens on which focal lengths are marked. Turning this ring will allow you to zoom, that is change the focal length. In some designs (not very popular now) you need to slide the zoom barrel forward and backwards to zoom. In the case of P&S cameras, you usually have a two way rocker switch which you can press

to increase or decrease the focal length.

Variable aperture

Constant aperture

In most zoom lenses, the light gathering capacity (speed of the lens) changes when you zoom. That is, if your zoom is 35-70mm, then as you change the focal length from 35 to 70mm, the effective lens speed could change, let us say, from f/3.5 to f/4.8. Such zoom lenses are called variable aperture zoom lenses. These lenses are specified as 35-70mm, f/3.5 -4.8. Most consumer grade zoom lenses are variable aperture type and so are the zoom lenses used on all point and shoot and bridge cameras. However, there are many high grade zoom lenses (very expensive!) that have constant aperture.

If you are using manual exposure control and a variable aperture zoom, then you must set the exposure after you select the focal length as the effective lens speed would have changed when you varied the focal

length. This is a precaution you must take. However, this need not be the case if you are using automatic exposure modes ( with TTL metering) since the camera will compensate for the change in lens speed by itself.

Now that you know how lenses are classified, the table below will serve you as a handy guide.


Types of LensesType Diagonal Angle Focal Length for Focal Length for Best suited for of View (AOV) 35mm or full APS-C sensor based frame D-SLRs D-SLR (1.5x)

Ultra-Wide-angle 84 degrees or more 24 mm or less 16mm or less Landscapes, architecture, interiors, photojournalism.

Moderate 84 degrees to 24 mm to 35 mm Approx.16 to 24mm General purpose,Wide-angle 62 degrees landscapes, photojournalism

Normal Around 46 degrees 40mm to 50mm Approx.25 to 35mm General purpose, candid, low light

Short to Medium 28 to 12 degrees 80mm to 200mm Approx.55 to 135mm Portraiture,Telephoto candid, photojournalism

Super Telephoto 8 degrees or less 300mm or greater 200mm or greater Sports, racing, wildlife, birds

NoW LET US Look aT SoME SPECIaL PUrPoSE LENSES DESIgNED For SPECIFIC aPPLICaTIoNS. Macro Lenses: These have a special focusing mechanism (helical) which greatly extends the lens elements away from the focal plane so that you can focus very close to the subject. This in turn allows you to take pictures with high magnifications. Technically speaking, a lens can really be called macro only if it can provide a magnification of at least of 1:1 or more. This means that size of the image must be the same as that of the subject or larger. That is, if you photograph a 10mm length object, its image on the sensor (regardless of the size of the sensor) should be 10mm (for 1:1) or larger. These lenses are also optimized to work best (offer best performance) at very short subject distances.

Macro lenses are available in several focal lengths starting from around 50mm to 200mm. Macros with higher focal lengths provide the same magnification for a larger subject-to-camera distance. For example, a 200mm macro lens will allow greater working distance than a 50mm macro lens for the same magnification. This can be useful in nature photography. After all you would not want to photograph


a scorpion from 2 inches! Greater working distance (the distance from the front of the lens to the film/sensor) also allows you greater freedom of arranging lights/reflectors.

You may ask what about your zoom which offers macro focusing. Is this is not a macro lens? Really speaking it is not. The word macro in this case is more an attribute of marketing than true optical performance. These lenses offer around 1:4 magnification (that is, the image on the sensor is 1/4 the size of the subject you are photographing) at best and that too with some compromise in performance. They can be called close-focusing, but certainly not macro. However they can be useful in a pinch.

Nikon calls macro lenses as Micro lenses. This is just a commercial nomenclature and has no bearing on the actual performance.

Mirror Lenses: These are telephoto lenses which have mirrors inside to fold the light path so as to reduce the overall physical length of the lens. Hence they are compact and lighter as compared to a conventional telephoto of the same focal length. They also have little or no chromatic aberration and provide good quality images. They

Shot with a normal lens Shot with a macro lens


Macro lens focused at InfinitySame lens focused at 1:2 (one half life size).

Note how the lens is now extended.

This picture shows a 50mm Normal lens (left), a 300mm

Mirror lens (middle) and a 300mm lens (right) of conventional design.

Note the very small size of the 300mm mirror lens compared

to a conventional 300mm lens. In fact it is just a little larger than a

50mm lens.

have two disadvantages. One is that, due to the way they are constructed, they offer only one fixed f/number. Second disadvantage is that they produce peculiar out-of-focus highlights which look like bright doughnuts. This type was once quite popular but of late they seem to have fallen out of favor with none of the major brands offering mirror lenses in their product lines at present.

Fish-eye Lenses: Originally developed for scientific purposes, these are extreme wide-angle lenses of very short focal lengths. They do not correct for barrel distortion and in fact emphasize this. They come in two types. The first is called the circular fish-eye. This produces 180 degree coverage all around and this creates a circular image within the frame.


The second type called full frame (not to be confused with the full frame format) has a diagonal angle of view of 180 degrees and produces an image that covers the frame fully (and hence the name). This type is more popular these days.

Picture taken with a Fish-eye lens. Note the pronounced barrel distortion (curving of sides).

Apart from scientific uses, these are useful for industrial photography and for photographing interiors and other cramped situations. Interestingly, in some cases it is possible to take highly distorted image from a fish-eye lens and process it through software to get an ultra-wide-angle effect that is distortion free.

Tilt and Shift Lenses: These lenses bring view-camera type movements to D-SLRs. They have the ability to tilt or shift (a part of ) the lens. When used together or individually, these movements allow tremendous control over depth of field. Another common application is in architectural photography when tilting a camera to include a tall building makes the building look as if it is tilting backwards. This can be corrected very well with this type of a lens. Also the lens can be shifted in such a way that the photographers shadow or reflection which might appear in the photograph, is eliminated.

Due to these characteristics they are widely used in table-top, architectural and landscape photography. These are specialized lenses and are expensive. Also, a certain amount of skill and understanding about how tilt and shift movements work is needed to use them effectively.

Tele-Converters: Also known as Tele-Extenders, these are not lenses in the sense that they cannot be used independently by themselves. They are mounted between the lens and a D-SLR body and are generally available with multiplication factors of 1.4x, 2x and 3x. When using a tele-converter you need to remember the following:


The 1.4x, 2x and 3x tele-extenders increase the focal length of the lens by a factor of 1.4, 2 and 3 respectively. However, there will be a corresponding light loss. You will lose 1, 2 and 3 stops of speed respectively.

As an example, if you use a 100mm f/2.0 lens with a 2x tele-extender, you will get 200mm in focal length. Unlike cropping this is a real increase in focal length; but your lens speed will decrease by two stops from f/2.0 to f/4.0.

Unless it is a very high quality tele-extender (and these are not cheap) there is a loss of quality. 1.4x converters provide the best image quality while 3x converters provide the worst. Also, tele-extenders work best with prime lenses rather than zooms.

A 2x Tele-Converter with a 300mm telephoto lens

There is one more factor that you need to consider. Most current autofocus systems work with apertures of f/5.6 or faster. So if you have a lens whose maximum aperture is f/5.6, and you add a tele-converter, the autofocus may not work effectively. If you have a lens whose maximum aperture is f/4.0, you can use it only with a 1.4x extender to autofocus, when the effective maximum aperture will become f/5.6. The focal length will of course increase by 1.4 times too. With a 2x converter, the effective aperture will become f/8 and manual focusing will now be the only option available.

With that, you now know all about the lenses to make a knowledgeable decision on your lens purchases.

So which is the best lens for you? A lot depends on the type of subjects and how you want to use a lens. These have been listed in the table Types of Lenses

To sum up, if you want a point and shoot camera, you can start with a camera which has a zoom lens covering a range from 28 to 105mm (35mm equivalent). This covers a lot of picture taking situations and the most popular subjects sceneries, portraits, holidays and family pictures. A bridge camera will give you lot more telephoto reach.


If you want to go the D-SLR (of APS format) route, it is best to have two lenses one zoom covering 18-55mm and another covering 55-200mm. These two lenses along with a D-SLR will be a good starting point for serious photography. This kit will cover most of the normal photographic situations. An alternative could be to have an all in one zoom of 18-200mm. This will give you the advantage of a single lens. Expect to pay more for this convenience and perhaps a little loss in quality compared to a two lens solution.

If you are more into wildlife or sports photography, you may want to consider a 70-300mm lens (at the minimum) instead of a 55-200mm lens. When you are going beyond 200mm, it is best if you go for a lens with image stabilization unless your camera body itself supports stabilization.

Here is one important point. Telephoto lenses (with focal lengths greater than 300mm) with their long physical appearance are sort of glamor lenses. However, they are more restrictive in application. Unless you are into the specialized genre of wild life or sports photography they are generally less useful than lenses with medium focal length range that is from 28 to 105mm (35mm equivalent).

Remember one thing. The quality of the image depends greatly on the lens, more than anything else. Many photographers make the mistake of buying an expensive camera body and a cheap lens. It is wiser to make your purchase the other way. Also, lenses do not get superseded as quickly as the camera bodies. So your investment is protected for longer.


Pixel Count and Print Size

If you tell your friend that you bought a digital camera, his first question will be How many megapixels does it have? Or, if someone is buying a digital camera and he is seeking your advice the most probable question he will ask is How many megapixels should my digital camera have?

This illustrates the importance, given to this very important specification of any digital camera, the number of megapixels it has. However, is the importance given to this figure justified? What is the impact of number of pixels on the image quality, real or perceived, and if real, to what extent? How does this affect the ultimate form of any image, which is the print?

This article will look into this aspect plus others such as the effect of pixel size, sensor size, resolution, etc. Before we can discuss in detail about all these issues, you need to get to know the terms pixel, pixel count, resolution and more importantly the difference between the last two.

Pixel Count: The sensor is a device placed in the camera body, and it is here that the light rays from the lens focus. It is manufactured with light gathering (photosensitive) elements arranged in rows and columns forming a rectangular grid. These elements produce an electric charge proportional to the intensity of the light falling on each element. This means more the light, the greater will be the electrical energy. The circuitry on board the camera measures this energy and hence knows the intensity of light at each photo element. By putting together measurements taken for each element, the on board computer is able to construct the entire image. Each dot of the image thus formed corresponds to one element. Each of these elements is called a Pixel, which is the short form for picture element. The number of pixels that are present in a sensor is called the pixel count and is normally specified as Mega (or millions of ) pixels (abbreviated as MP).


However, not every pixel will contribute to the image. A certain number of pixels will be allocated for non-image forming tasks. If you subtract these from the total pixels then you will get what is called the effective pixels.

Pixels, as you have just read, are arranged as a rectangular grid in columns and rows. Hence, it is customary to specify them that way. That is, a 12 MP sensor will have 4,300 columns and 2,800 rows for example.

resolution: So, if this is what pixel count is, what is resolution? Resolution is the resolving power and is measured as number of lines per millimeter or inch. That is, it basically tells the detail that a camera can capture. Resolution depends on the number of pixels, lighting conditions, the test target, the resolving power of the lens and so on. While this is an important measure there are so many variables involved as mentioned that no camera manufacturer mentions resolution. It is more often used to measure the resolving power of a lens. Another place where the term resolution is used is when you print (more of this shortly).

Unfortunately these two terms - pixel count and resolution are used interchangeably by many, even though international standards specify that it should not be so used in digital imaging. Many websites say the same thing and even some books say so. But this is not correct. The pixels that a digital camera has (for example 12 MP) is called the pixel count and this is not the resolution. If you have any doubts refer to a digital camera specification sheet from a standard camera manufacturer like Canon or Nikon and see what is printed in them.

On the other hand, you need to understand the significance of the word resolution when the captured image is printed (or shown on a monitor). As demands of printing are much higher than displaying on a monitor, we will confine the discussion to printing issues in this article, but the principles are the same.

A print is composed of a number of dots. Each dot corresponds to a pixel that has been captured by your camera. As you can expect for a given print size, higher number of


dots and smaller sized dots will allow you to see finer detail in a print. So how many dots should be there in a print and what should be size of each dot? To have a norm regardless of the print size this requirement is specified as the number of dots needed per inch. This is abbreviated as dpi and is known as the print resolution. The generally accepted print resolution is 300 dpi. It is not necessary to have resolution beyond this as the human eye cannot resolve beyond this number. Music aficionados will recollect that there is a similar limitation for our ears we cannot hear any frequencies beyond 20,000 Hertz. (In fact most people beyond the age of 40 cannot hear more than 16,000 Hertz)

The number of pixels in your camera has a direct bearing on the size of the print you can make. The following example will make this clear. If you take a 12 MP image of 4300x2800 pixels and print at 300 dpi, it will yield a print of approximately 14.5x9.5 inches. This is called printing at the native resolution.

If you want to print beyond this size, say 30x20 in with the same number of pixels what one needs to do is to distribute the same number of pixels over a larger area. This will automatically make the dots proportionally larger and will bring down the number of dots per inch. In other words the print resolution reduces. As an example a 12 MP image printed at 30x20 in will have a resolution of only 140 dpi. There will be a corresponding loss in detail (sharpness) of the print.

So what is that you need to do to make very large prints? There are four options available. option 1: This is the simplest option do nothing! Just make a print at lower resolution (for a large print a resolution of 250 dpi is acceptable). This is because as the print size increases you will start looking at the print from a longer distance. As the distance grows the eye will not be able to resolve that much. However, the print will look relatively worse if you look at close quarters. This is the reason bill boards that look fine at large distances will look really fuzzy if you go near them!

If your camera has enough of a pixel count to give you say a 30x20 in print at 250 dpi, then perhaps you need to do nothing unless you are making a print for a very critical application (like hanging in a gallery). option 2: This is the most popular option to print beyond the native resolution. This


is called up-sizing (or sometimes ressing up) through a process called interpolation. In this process the number of pixels is increased beyond what has been captured by the sensor. Thus you can print beyond the native resolution. Interpolation works as follows. Remember that the pixels in a sensor are organized as a rectangular grid, perfectly in rows and columns. Due to this very regular structure it is mathematically possible to find out and insert pixels between the existing pixels, thus increasing the total number of pixels.

Most standard image processing software packages (like Photoshop) have facilities to support interpolation. Thus, you need not worry about all the mathematics (which is actually quite complex) that goes on behind interpolation!

Interpolation sounds like a magic bullet and that is true to a certain extent. However, there is a limit to what extent you can increase the file size. You can safely (based on my personal experience) increase the total number of pixels by a factor of little more than four. So, if you start with a 12 MP camera which gives a print of only 14.5x9.5 in at native resolution, you can go up to 54 MP which will give a print of 30x20 inches at 300 dpi. Also note that for the interpolation to give best results, the quality of the original pixels should be very good. This means that you should have used a good lens, held the camera steady, image should have been properly exposed and so on.

Note: Sometimes you may want to make the image smaller too. This is done when you want to display the images on a monitor, as high resolution is not required. Also, large files take time to transmit through email, upload to sites like Flickr, Facebook etc. So for these cases you may want to reduce the size. This operation is called down-sizing. The common name for up-sizing and down-sizing as you would expect is re-sizing.

option 3: This is the best and most expensive solution! Simply use a camera that has a higher pixel count. If you use a 24 MP camera then you can make a 300 dpi print of 20x13.5 in at the native resolution itself. This is a clear case where higher resolution helps. In fact the main advantage of cameras with higher resolutions is their ability to make large size prints yet retain detail.


option 4: There is a way you can get more megapixels from your existing camera without spending anything. That may sound incredible, but it is not, provided your subject is suitable. The technique is similar to that of panorama making. Switch to a longer focal length (so only a smaller area is covered) and take overlapped images and stitch them together to cover the full area. If you do not change your position then perspective will not change. So, the stitched image will look the same as that taken with a shorter focal length lens, but it will have lot more pixels, since you have now used multiple images. There are now devices like Gigapan that perform this task automatically.

The subject needs to be static so this technique is not suitable in all situations. However, you can use it for landscapes where high resolutions are needed.

Table showing different print sizes at various dpi and corresponding pixel count needed

Print Size dpi MP Horizontal Vertical in inches (approx) Pixels Pixels

10 X 7 300 6 3000 200014 X 9 300 12 4300 280020 X 13 300 24 6000 400024 X 16 250 24 6000 400025 X 16 300 36 7350 490030 X 20 250 36 7350 490030 X 20 300 54 9000 6000

Note: The computer monitors as of now are manufactured to a resolution of around 100 dpi (or less). Thus the demands from an image are higher if you want to print it rather than just display it.

ProS aND CoNS oF HIgH PIxEL CoUNTS: Apart from getting large prints, there is also another advantage with high pixel counts. This is in cropping. That is, many times you take a captured image and discard a part of it for compositional reasons. Obviously, after you throw away some pixels, you will be left with less. Thus, if you start with a 12 MP camera and crop out 4 MP the remaining 8 MP can


still produce a very good quality print. This is a bit of over simplification as several factors come into play but it does illustrate the concept. However, when you crop an image, you are discarding some pixels, and this will result in the reduction of the maximum print size.

Cropping can also be useful for wildlife and bird photographers as frequently they cannot go close to the subject. The result would be a image where the subject is small. By cropping you will be able to make the subject larger. For example, if you start with a 200 mm lens, you can get the effect of a 280 mm lens by cropping with a factor of 1.4. In this process however you will be discarding about 50 percent of the pixels not a very good solution but if you are starting with very high number of pixels and if the pixels are of very high quality then you will still be able to get a good print. As an example, if you start with 24 MP you can still get 12 MP after cropping - good enough for a nice big print.

Before you go for a very high pixel camera (they cost serious money), ask yourself how large you want to print and how often. Most of us do not print larger than 18 X 12 in. You can easily print this size with an 8 MP camera (with interpolation). The money instead can be better spent for more useful accessories like lenses, etc. Also, to exploit such very high pixel counts your lenses must be top notch. Dont expect a cheap kit zoom to provide enough resolution to fully use the 22+ MP of your new super duper D-SLR!

Very high pixels counts can be counterproductive too. They produce very large computer files, which are difficult to edit and store. More importantly the pixel size reduces for a given sensor size as the count increases. As you will see shortly, smaller pixel sizes produce more digital noise and have less dynamic range, reducing the overall quality of the image.

To conclude, pixel count, beyond any doubt, is one of the most important parameters, but not the only one that determines the image quality as many would believe. Its greatest impact is one on the size of the print you make as you have seen. In fact, the importance of pixel count has been over-hyped leading some educated critics calling the race to add more pixels as megapixel madness!

Pixel Count and Resolving power: How are these two linked? The following example will show you the relationship.


Let us take two hypothetical cameras (A and B) each of APS-C size sensors (24 X 18 mm) and have 1.5 MP and 6 MP.

Assuming that both have 1.5:1 aspect ratio, the pixels will be 1500 X 1000 (1.5 MP) and 3000 X 2000 (6 MP). Since the pixels are square we can either do the calculations in vertical or horizontal direction and both will give the same number.

Look aT THIS ExaMPLE - Camera A has 1500 pixels spread over 24 mm and hence the theoretical max resolution is 1500/24 = 62.5 lines / mm.

Camera B has 3000 pixels spread over 24 mm and hence the theoretical max resolution is 3000/24 = 125 lines / mm.

Now compared to A, camera B has double the resolution. However, the number of pixels (called the pixel count) in B are quadrupled (from 1.5 MP to 6 MP) compared to A.

This is the reason why for resolution to double, pixel count has to quadruple (become four times). In practice it has to more than quadruple since several factors like the resolving power of lens, etc., also have to be taken into account. So, if the next D-SLR model from your favorite manufacturer has just a couple of mega pixels more dont spring for it just for those extra pixels as you will get only minimum increase in resolution.

Talking of lenses, there are really few lenses today that can resolve beyond 100 lines/mm. This, plus diffraction effects will make it increasingly difficult to get high end resolution figures even if your camera is capable of! So these figures are what you can call theoretical maximum limits.

ProS aND CoNS oF a LargE SENSor:So what are the other features of the sensor that are important for picture quality? These are noise characteristics of the pixels and dynamic range. To understand these you need to look at the impact of the pixel size on these two features. Larger pixels have better light gathering capability simply because they have more area


to collect light. More light means a stronger signal. Hence, the unwanted signal (which is the noise) is less compared to the signal that is generated by light, which is what we want. This in turn means that you can get much better high ISO performance. This feature is invaluable for photographers who do a lot of photography in low light. It is also useful for sports and other action photographers since high ISO allows use of higher shutter speeds for the same light. Larger pixels give a higher dynamic range too that is they capture a greater brightness range from darkest shadows to brightest highlights.

If large sensors give better noise and dynamic range, why not go for larger sensors always? As the size of each pixel increase, it does not require a mathematician to guess that for the same number of pixels the size of the sensor also increases. Due to the way sensors are manufactured, larger the sensor size the more expensive it is to manufacture. This relationship is not even linear. That is, if the size doubles the cost of sensor goes up by more than two times. Not only that, the camera will now need a larger mirror, prism, and shutter to complete the picture. To add to this, lenses have to be bigger to cover the larger sensor and hence will be more expensive too! All this put together makes two systems (cameras plus lenses for DX and FX), both of which are otherwise very similar, to differ quite a lot in price if the sensor sizes are different.

Twins separated at birth! These two cameras have nearly identical specifications including the number of pixels. However, the one on the left uses an APS-C size sensor and the one on the right uses a full-frame sensor. Note the larger prism and mirror in the case of the full-frame camera to

cater to the larger sensor.

Let us look at one specific example. Here are two semi-p ro f es s i o n a l high quality D-SLRs made by the same manufacturer. These two cameras have nearly identical specs (including number of pixels) but one has an APS-C (24x16 mm) sensor and the other has a full frame sensor (36x24 mm). At the time of writing the cost of full frame


version was about 50 percent higher than that of the APS-C version! Before you rush out and spend mega-bucks on a D-SLR with a full frame sensor put these questions to yourself. How often do you photograph at ISOs greater than 3200 and print at or larger than 30x20 in? If the answer is frequently, then probably you should go for a full-frame D-SLR.

As technology develops, the cost of larger sensors will come down but the same technology will also drive the cost of the APS-C sensors down. The image quality too is improving continuously. So, as time passes smaller sensors will give better high ISO performance, superior noise control, etc. But these same technology improvements can also be applied to larger sensors resulting in even better picture quality. So which format will win? Answering that is not easy. As with everything in life the format that gives the best tradeoff between the three factors - cost, convenience and image quality will win. To give you an analogy, during the film days there were formats like medium and large formats (going up to a size of 10x8 in) that offered superior quality and then there were small formats like Instamatic 110 which offered great convenience and cost advantage. Plus there were countless other formats that did not make an impact at all. In the end 35 mm (with 36x24 mm) won over all the rest as it offered best tradeoff or it gave the best bang for the buck. Which digital format will be the rightful heir to 35 mm will be decided over time but the underlying factors that will decide (viz. cost, convenience and quality) will be the same.

Cropping factor and its influence on angle of view (AOV): The image below shows how a scene would look from the viewfinders of different cameras positioned at the same place and with a lens of the same focal length but with sensors of different sizes. As you can observe, cameras with smaller sensors see narrower angle (reduced angle of view). This means that progressively less and less area (also called field of view) is covered. This is similar to the effect you would get when you crop a picture. Technically the AOV reduces as sensor size reduces for the same focal length. But remember the focal length does not change! Due to reduced AOV and consequent coverage of lesser area, the lens of the same focal length will appear to you as if it is having a longer focal length. This has advantage for wildlife and bird photographers, since you can get more out of your telephoto lens but can be a disadvantage when using wide-angle lenses as what was a


wide-angle lens on your full frame lens will cover a AOV which is narrower. From this you can infer that you cannot classify a lens as a telephoto or something else just by looking at the focal length alone. The format (that is the sensor size) also needs to be taken into account. The factor by which the AOV reduces compared to a full frame is called the Cropping factor. It is the ratio of the diagonals of the two frames. The cropping factor is 1.5x for APS-C sensors (1.6x for Canons), 2x for Four Thirds System and will be even larger for point-and-shoot and bridge cameras. Suppose your lens has an AOV of 15 degrees on a full-frame camera. Now, if you mount the same lens on an APS-C sensor camera, the effective AOV will be only 10 degrees.

Many of us are used to classification of lenses based on focal lengths as used on 35 mm cameras. For example, we classify a 28 mm lens on a 35 mm camera as a wide-angle lens. Based on this, manufacturers mention the equivalent 35 mm focal length figure in the literature. Some manufacturers have even started to mark lenses with these focal lengths while at the same time not explicitly declaring so. This is not technically correct.

Image showing the different field of view of cameras with sensors of different sizes

1. Full frame (36 X 24 mm) 2. APS-C size (24 X 16 mm) 3. Micro Four Thirds System (MFT) 4. 2/3 inch Type 5. 1/3.6 inch Type


Most of the super zoom equipped bridge digital cameras have very small sensors and thus need only a short focal length to get a great telephoto effect. For example, if you study the specifications of a digital bridge camera that claims to have a super telephoto of 500 mm (equivalent focal length for 35 mm camera), you will find that the actual focal length is just about 90 mm. (This means that the cropping factor is about 5.5 times here). A lens of this focal length on a 35 mm camera would qualify as a short telephoto and on a medium format camera as a normal lens! So please dont get misled by such figures.

Sensor size and printing: Once a image is captured, the size of the sensor has no bearing on the printing. In fact the whole printing process is totally agnostic to the sensor size. This is quite unlike a print made from a film where the size of the negative plays a significant role on the size of the print made (for a given quality). You have seen that if you take a 12 MP and print at 300 dpi, it will yield a print of approximately (at native resolution) 14.5 X 9.5 in. This is regardless of the size of the sensor used. The prints too will be theoretically indistinguishable if pixels are of equal quality. However, this will not be the case in practice as a print made from a camera with larger pixels, will be of superior quality. This qualitative difference will be even more apparent in situations where:

1. High ISos have been used2. Light is low3. Scene had high contrast (that is scenes with high dynamic range)

How many pixels does film have? This question is likely to open a can of worms and the Editors are sure to receive letters from both film and digital aficionados contesting what I am going to say. To make the issue as non-controversial as possible, I will resort to some mathematics with the hope that numbers cannot be disputed. To make this easier to understand let us assume that our film frame is a standard 35 mm frame of 1.5x1 inches (or 36x24 mm). It is generally accepted that if you scan at about 4000 dpi you can capture all the information from even the finest grain film. If this is the case, the scan of 1.5x1 inch frame will yield (approximately) 6000x4000 pixels or 24 MP. This number circulates a lot everywhere and is correct.


The wrong notion is the one that comes out as a deduction from it that is, you need a 24 MP camera to produce the same quality of image of a 35 mm. Sorry, film aficionados but you dont need that many megapixels to produce an image of equal quality. This is because of the interpolation that was explained earlier. A 24 MP scan (6000x4000 pixels) will yield a print of 20x13 in (at 300 dpi), something that an 8 MP D-SLR can produce with just moderate interpolation! Today a top of the line 22 MP+ D-SLR can produce prints with the quality of a medium format film camera as per some experts and tests.

So, the next question that comes to you is that, if interpolation is doing the trick for images captured by digital cameras, why not start with a scanned image and interpolate beyond the 24 MP to get an even bigger print? Unfortunately, this does not work, since the scan is of a film, which is composed of random grains (no regular structure) and hence is not amenable to interpolation. Scanning beyond 4000 dpi is not productive either since there is not much to capture. The only solution for getting a bigger scanned file is - you have guessed it - to start with a bigger film format like medium or large format.


File FormatsJPEG, TIFF, NEF, CR2, PSD, DNG ... and what not! Confused? Not to worry! This alphabet soup simply indicates the format of a file and you probably know that already. But what is the significance of this format and before that, what is a file? That is what we will see in this article what a file means the different types of popularly used image files, their relative merits, and when to use which format.

First some background. Electronic cameras capture images through a light sensing medium which is the sensor. However, though not commonly known, all cameras which capture images electronically this way are not digital cameras. So, what differentiates digital cameras from other electronic cameras?

The light that falls on the sensor produces an electric charge proportional to the intensity of the light falling on the sensor- more intense the light higher the charge. The charge is converted into an electric current. This is what is called the signal. This signal can be written as it is on a storage medium like tape. While this sounds unusual, till digital video came, all the video recordings were recorded this way (remember the VHS tapes?). So, what if you write still images from a camera too on a tape? Such cameras existed for a very brief time and were mostly used for press photography, etc. They never made it to the consumer world due to poor quality of the image. These are really what you can call analog cameras electronic guts but not digital recording.

There is a tendency by the uninformed to call film cameras as analog cameras. This is not correct since film cameras capture images on film and not on electronic sensors. Except for exposure and other controls, film cameras do not need electronics in any way. Chronologically, analog cameras followed film cameras and were very quickly superseded by digital cameras.

Going back to the signal, what you do with this signal next is important. In a digital camera instead of recording the signal as it is, it is converted into a digital stream (ones and zeroes)


with the help of what is called an Analog-to-Digital Converter (ADC). The digital stream is then stored on the memory card as a file. This process, creation of a file, is what makes a digital camera different from its analog forebears. A human cannot interpret a file as it is just a seemingly endless stream of random ones and zeroes. However, a computer can!

But why take this extra step of conversion? That is because once the signal is converted into a digital file the benefits are innumerable. For example, digital files can be processed by a computer in myriad ways. A file is given a definite structure so that the software running on the computer can interpret all the ones and zeros and make sense out of the whole thing. This structure, that is, essentially the way the sequence of ones and zeroes are organized is vital and without a rigid definition of this, a computer cannot make sense out of a file. The structure of a file is also called the file format and this is not to be confused with the formatting of memory cards. In the latter case, you are creating a framework on the memory card or disk. This is needed for writing, organizing and retrieving files.

It is this recognizable pre-defined structure that will enable the right software to interpret the contents of the file for you in a meaningful way. Thus, if you have an image display software it will interpret an image file and show you your holiday picture. Likewise if you have a music playing software, it will play Jai Ho from a music file for you. Of course the software that plays music for you cannot show a picture since it cannot interpret an image file. Its job is to play the music.

Each file has to have a name the computer (and of course you too) surely cannot make out which image is what without each file having a unique name. Plus, the computer should also have a way to find out the type of the file. For example it needs to distinguish an image file from a music file. Hence the file type is also included in the file name and is called the extension.

Thus, you can have an image file called taj mahal.jpg and a music file called jai ho.mp3 where taj mahal and jai ho are files names and jpg and mp3 are extensions.

There is one more concept that you need to be aware of before we can go deeper. This is called compression. Generally an image contains a lot of information that can be


easily represented in a short hand fashion with the help of mathematics. Due to this the size of the file can be reduced or compressed quite drastically. The natural question that comes to our mind is, will compression reduce the quality? The answer could be no, may be or yes. Before you conclude and say that the author is being evasive believe it or not, it is possible to have all three ways of compression.

If the compression is done in such a way that there is absolutely no loss of quality then it is called lossless compression. This is very much technically possible though it may not reduce the size much (see File Sizes table elsewhere). If you compress with loss of quality then it is called lossy compression. If you choose a low compression factor, the loss can be insignificant and the resulting image will be good enough for most applications. On the other hand if you choose a very high compression factor, the size of the file will reduce drastically with a corresponding decrease in quality.

With that as the background we are now ready to look at the different types of image files that we will come across in photography. To start with, be aware that there are a huge number of file formats in existence and it is just impossible to cover all of them. Nor is it necessary since there are really only a few important image file formats that are widely used these days though there are lots of variations within these. The most commonly used file formats are 1. JPEg\ 2. raW 3. TIFF4. PSD 5. DNg

We will see each of them in detail:

JPEg format: JPEG is an abbreviation for Joint Photographic Experts Group. It is the group that formulated the specifications for this file format. Without any question, JPEG is by far the most widely used file format. Today there is probably no digital camera that does not support JPEG files it is that universal.

After an image is captured by the sensor, the on board computer of your digital camera adds color information, and then processes the image, using the various parameters that you have chosen in the camera. These include saturation, contrast, sharpness, White


Balance, etc. The processed image is then compressed and written as a JPEG file in the memory card inserted in your camera. Since the processing has been completed the parameters are already incorporated into the JPEG. Hence, it is very difficult to change them. Just try to reduce sweetness in a cup of coffee after it has been made !

While all D-SLRs capture RAW data with an accuracy of 12 bits per each channel (red, green and blue), JPEG retains only 8 bits per each channel thus inherently reducing the fineness in gradation of tones. In addition JPEG is essentially a lossy format. Because of this there will be loss of data and hence the quality of the image will suffer, especially if a high compression ratio is chosen. The loss of quality normally shows up as artifacts that is, unwanted features that were not originally present in the image.

In spite of these shortcomings, JPEG format is used exclusively for all web applications. It is also very compact (that is small) and is ideally suited for transmission over the networks. Today it is really the only format that is universally read by every computer in the world. It is also the format accepted by any competition or salon where digital files are used for submission. Since JPEG files are small, cameras can record them at high speed. Most of the cameras which support high continuous burst rates use JPEG while doing so. This is invaluable for sports and other action photography.

Also, most of the printers that are available commercially (e.g. Fuji Frontier) accept JPEG files. Hence if you are sending files to a commercial lab for printing you need to convert the files to JPEG format.

Most cameras offer at least three grades for compressing your files in JPEG format. The names could differ from manufacturer to manufacturer. Here is one example:

JPEg Compression remarks

Fine Best image quality, largest file size

Normal Via media moderate image quality

and size

Basic Least image quality, smallest file size


Tip: Every time you save a JPEG file, it tries to compress the file with a corresponding loss in quality. Hence, do not try to repeatedly save a file in JPEG format while editing. If you need to edit a file and save it in between editing, use another format which is lossless. You can save it as a JPEG after you have finished editing, just before printing or publishing on the web.

Effects of compression

Quality: Large and Fine Quality: Small and Basic

Saved with a quality setting of 12

Saved with a quality setting of zero

In Camera

In Photoshop

raW file format: The word RAW is neither an acronym nor an abbreviation. RAW is just raw as in un-cooked food and that is a very apt analogy. A RAW file unlike a JPEG file is unprocessed. If you open a RAW file with a RAW Converter (which is just a software program) in your computer, then you will be able to see the image as if the parameters have been applied but this effect is only visual. So, the RAW Converter allows you to see


the effect of the parameters without really applying them. Due to this you can change them at will to the values you like. You can now ask the computer to process the RAW file. At this time, the parameters that you have chosen will be incorporated into the image (baked as a part of the image) and a processed image file will be generated. The format of this can be PSD or JPEG or TIFF or some other, based on your choice.

Since a RAW file is unprocessed it is also called a digital negative. The RAW file has at least 12 bits per each channel and hence has a lot more data. The more advanced cameras support 14 or even 16 bits per channel. Hence, the RAW format gives you smoother tonal gradations, better latitude (one to two stops more than JPEG) and also better dynamic range. RAW images also exhibit less of a tendency to suffer from sudden blowout of highlights.

Some cameras allow RAW file to be compressed. In many cases (there are a few exceptions) a compressed RAW file is loss less.

RAW file editing is generally non destructive. What happens is that when corrections/editing is done in a RAW converter, the changes do not affect the RAW file itself but are stored separately. Hence, it is easy to go back and change any editing you have done. This is an invaluable feature. When using ACR, the editing changes that you do are stored in a separate sidecar file called the .xmp file.

If RAW has so many advantages, you may ask, why is that many photographers dont use it and many cameras (mostly P&S cameras) dont even support it? There are two main reasons for this.

First a RAW file is not usable straight away as it comes out of the camera, the way you can use a JPEG. It cannot be put on a website (like Flickr). It cannot be printed. It must necessarily be processed in a computer, something many do not want. For these reasons most P&S cameras do not even support RAW

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