bare bones camera-01

8/2/2019 Bare Bones Camera-01

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1. BasicsTHE CAMERA HOWIT WORKS

The camera is an imperfect imitation of the human eye. Like theeye, it sees by means of a lens which gathers light reflected offobjects. The lens directs this light onto a surface which senses thepattern formed by the differences in brightness and color of the different parts of the scene. In the case of the eye, this surface atthe back of the eye sends the pattern of light to the brain where itis translated into , an image which we "see."

THE EYE GATHERS PATTERNS OF REFLECTED LIGH.T WHICHTHEBRAIN TRANSLATES INTO IMAGES WE SEE.

In the case of the camera, the lens directs the patterns oflight onto a variety of sensitive surfaces. Still cameras recordlight patterns on film coated with ligh .t-sensi tive chemicals. Thechemicals react differently to different amounts and colors of light,forming a record, or image of the light pattern. After the film isprocessed in other chemicals, the iEage becomes visible.


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STILL CAMERAS RECORD LIGHT PATTERNS ON FILM COATEDWITHLIGHT-SENSITIVE CHEMICALS.

You'll notice that both the lens of the eye and the lens of thecamera turn the light pattern upside down as it passes through. Thisis because they're both convex lenses, or lenses which curve outward.Because of their physical properties, convex lenses always invertimages. In the brain, and in the camera viewfinder, t he images areturned right side up again.

Movie cameras record images in the same way as still cameras,except they do it more ofteno Eight-millimeter movie cameras normal-ly take 18 different pictures every second. Sixteen millimeter andthirty-five millimeter movie cameras normally take 24 pictures, orframes, per second. When these pictures are projected on a screenat the same fast rate, they give the illusion of continuous movement.The viewer's mind fills in the gaps between the individual frames,due to a physiological phenomenon known as persistence of vision.

-------------------------------------MOYIE CAMERAS TAKE MANY DIFFERENT PICTURES EVERY SECOND.


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Like a movie camera, the lens of a television camera focuseslight patterns onto a light-sensitive surface. In early TV cameras,this was an electronic tube. In most modern cameras, it consists ofone or more CCDs-charge coupled devices-which are small flat chips.Each CCD chip is made up of thousands of tiny light-sensitive areascalled picture elements, or pixels, which change according to thecolor and intensity of the light hitting them. The image formed byall the pixels taken together is electronically collected off thechip at a rate of thirty complete .i ma ge s per second, which can be

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TV CAMERAS CONVERT LIGHT PATTERNS INTO ELECTRONIC IMAGES

At the TV set the process is reversed to recreate the originalimage. Persistence of vision causes the viewer to perceive thethirty separate pictures per second as continuous movement .


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4EXPOSURE

Exposure is the amount of light that comes through the lensand hits the film or CCD chip. The hole in the center of the lensthat the light travels through is called the aperture. If theaperture is big, it lets in lots of light. If it's small, it letsin very l i t t l e light. The size of the aperture is adjusted by thef/stop ring on the outside of the lens. An f/stop is simply ameasure of how big or how little the aperture is.

I find that the easiest way to understand f/stops is to thinkof them in terms of fractions, because that's what they really are.F/2 means that the aperture is 1/2 as big across as the lens islong. F/16 means that the aperture is 1/16th as big across as thelens is long.

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When you look at it this way, it's easy to understand why in adark room, you 'll probably be shooting at f/2 to let in all thelight you can. Conversely, outside in bright suniight, whereyou 've got a lot of light, you 'll probably stop down to f/l1 orf/16, to let less light in.


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Now that you unders tand that, let me point out that in mostmodern lenses, espec ially zoom le nses, what I've just told you i s n ' tabsolutely true. An f/2 aperture won't phys ically be exactly 1/2 t helength of the lens. But optically it will be . It wi ll let throughas much l ight as if it were i ndee d 1/ 2 the length of the lens. Andthat 's the important thing.

F/stops are constructed so that as you go from f/ l to f/22 andbeyond, each stop admits 1/ 2 as much light as the one before. Theprogression is: f/l, f/l.4, f/2, f/2,8, f/4, f/5.6, f/8, fill, f/16,f/2 2, f/3 2, f/45, f/6 4, and so on . F/l.4 admits half as much lightas file F/4 admits half as much light a s f/2.8.

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6COLOR TEMPERATURE

Have you ever been out walking on a cold, dingy day andremarked to yourself how warm and cozy all the lighted windowslooked? Well, that was because the light in the windows of awarmer color that the light outside.

Yes, light comes in different colors. If you think about it,you'll see it's true. There 's the red glow from an open fire or asunset; the bluish cast of a sky dark with rainclouds; and thatblue-green ghoulish look you get from the fluorescents in all-nightpizzerias. As a general rule, our eyes adjust so well to thesedifferent colored light sources that we hardly notice them. Not sothe camera.

Color films and CCD chips can handle only one color of lightsource at a time and reproduce colors accurately. They do this bymeans of color temperature and color filters.

Color temperature is a way to identify different colors oflight sources. It's measured in degrees Kelvin, after Lord Kelvin,who devised the system. It's written like this: 2500K.

The idea is, you take a perfectly black body, like a piece ofcoal, at absolute zero (-273C), and start heating it up. As itgets hotter, it puts out different colors of light: first red, thenblue, then bluish-white. The different colors of light areidentified by the temperatures at which they occur. 2000K is thereddish light produced at 2000 degrees Kelvin. 8000K is the bluishlight produced at 8000 degrees Kelvin.

As I mentioned above, color films and CCDs can handle only onecolor of light source at a time. To take pictures under adifferent colored light source, color filters are used to convertthe existing light to the color temperature required.


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7Professional TV cameras have built-in filters, which you set

according to the light you'll be shooting under. A typical filterselection might include: TUNGSTEN-INCANDESCENT3200K); MIXEDTUNGSTENANDDAYLIGHT/FLUORESCENT4300K); DAYLIGHT(5400K); andSHADE (6600K). (Fluorescent light , strictly speaking, has a discontinuous spectrum and doesn't fit into the Kelvin system; nevertheless,a 4300K filter setting will permit us adequate color reproduction.)

Once you select the correct filter on a TV camera, you fine tunethe color by adjusting your white balance. This procedure variesfrom camera to camera and can be as simple as pushing a single button. It assures that the whites in your scene reproduce as whites;the other colors then fall into place.

Color movie films are manufactured for two kinds of light:3200K-Tungsten; and 5400K-Daylight. If you shoot tungsten film intungsten light, you don't need a filter. Likewise if you shootdaylight film in daylight.

To shoot tungsten film in daylight . put a #85 filter on thefront of the lens or in a filter slot on the camera. This orangefilter converts 5400K daylight to red 3200K tungsten light.

To shoot daylight film inside with tungsten light, use a #80Afilter. This blue filter converts red tungsten light to blue daylight. For photoflood lights (3400K), us a #80B filter.SETTING EXPOSUREON A TV CAMERA

First, select the correct filter and adjust your white balance,as discussed in the preceding section on color temperature.

If your camera has automatic exposure and you can't turn it off,about the only control you have is to avoid large light areas andlarge dark areas within the frame. These will throw your exposure off.


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Professional TV cameras have both auto and manual exposure. Tomanually change your exposure, look in the viewfinder and move thef/stop ring until the picture looks good. (Most cameras also have anindicator in the viewfinder to tell you when your exposure iscorrect.) With a new or strange camera, it's a good idea to make atest recording under various lighting conditions and play it back ona good monitor to check the calibration of your camera's viewfinder.Sometimes you'll have to go a little darker or a little lighter inthe viewfinder to get the best color on playback.

The main problem with TV cameras is large areas of white, particularly those caused by strong backlight-light shining toward thecamera from behind the subject. If you include too much pure,bright white in your frame, all the other colors go dark . Sometimes the white will "bleed" over into the other colors. Whiteproblems are seen clearly in your viewfinder, so they're easilyavoidable by moving the camera or subject or both, or by changingyour lighting or scenery.SETTING EXPOSURE ON A FILM CAMERA

ISO. Check .t h e film label to see what ISO your film is. ISOstands for International Standards Organization. The ISO numberindicates the speed or sensitivity of the film . The lower thenumber, the less sensitive, the "slower" the film is, and the morelight you need to get a usable picture. The higher the number, themore sensitive, the "faster" the film is, and the less light youneed to get a usable picture.

Film speed may also be indicated as ASA, for American StandardsAssociation, or EI, for Exposure Index. For all practical purposes,ASA and EI numbers are equivalent to ISO numbers.


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9ISO numbers progress geometrically in terms of s e n s i t i v i t y

Each time you double the ISO number, you halve the amount of lightneeded to get a usable image.

...... 1 I / "- //0 ,/ ,- W -" \ I I~ /- /- :1:,-g .; \D::)- \' I,:Ji ...- ,.- - ~ ,\I ( , X - - - ~ - ,\.\1 /,, , t tI /- -I I ... ....", ...... -- ..... ' .....; , - , ...ISO Z? 50 100 'J(X) eEACH TI ME YOU DOUBLE THE ISO, YOU CUT YOUR LIGHT REQUIREMENTIN HALF.Slower, low ISO films generally produce a higher quality picture.

Faster, higher ISO films, while requiring much less light, generallyproduce grainier, lower quality images.COLOR TEMPERATURE. Make sure the color temperature of your film

is the same as the color temperature of the light you're filming under. If not, put on a #85 filter to use tungsten film in daylight;or put on a #80A filter to use daylight film in tungsten light.

Remember, any time you use a filter on the camera, you're re-ducing the amount of light reaching the film. This means you haveto have that much more light entering the lens, to compensate for thelight soaked up by the filter. Since your light requirements havegone up, you've effectively lowered your ISO. Look once more at thechart above and you'll see what I mean: higher light requirementequals lower ISO number. To determine the correct ISO for the film-filter combination you're using, check the manufacturer's informationsheet for that particular film.


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10LIGHT METERS. Light meters measure the amount of light hitting

them. Then, based on the ISO of your film and the number of framesper second you're shooting, they tell you what f/stop to set for thebest exposure of your sceneo

For all intents and purposes, light meters see everything in blackand white, in terms of lightness and darkness. They don't react tothe color of a subject, only to its lightness or darkness.

On"most cameras with built-in meters and on hand-held light metersyou must manually set the ISO. The method varies, but be sure youdo it. Otherwise, the meter won't know how much light your film re- ..quires and will give you incorrect exposures.

Overexposure means you let too much light in--the picture is toolight, washed out. Underexposure means you didn't let enough lightin--the picture is too dark.

USING A LIGHT METER. If you have an automatic exposure camera andyou can't manually override it, all you can do is try to avoid largelight and dark areas in your frame, which will throw your exposure off.

On-camera exposure meters are called refZective meters. Theymeasure the light refZected at the camera by whatever it is you'repointing the camera at. Handheld reflective meters work the same way o

ON- CAMERA AND HANDHELD REFLECTIVE LI GHT METERS MEASURELIGHT REFLECTED OFF THE SUBJECT.Reflective meters "work on the basis of a theoretical average sub-

ject which is gray and reflects 18% of the light hitting it o (You canbuy an 18% Gray Card from Kodak.) No matter where you point it, the


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11meter will tell you the f/stop needed to reproduce that subject as .if it were 18% gray. This usually gives you a satisfactory exposure.

, Howeve r , for lighter-than-average gray subjects, you have to open upyour aperture to reproduce the subject as lighter than 18% gray. For

"'\darker-than-average subjects, close down to let less light in and re-produce the subject correctly as darker than 18% gray. How much, youhave to learn by experience.

For most film work, the best way to measure light is with a hand-held incident light meter. The incident meter has a white half-spherewhich you hold in front of your subject, pointing toward the camera.The meter measures the light falling on that particular spot and cal-culates an f/stop for an average 18% gray subject. (It's essentiallythe same as taking a reflective reading off a gray card held in frontof your subject.) This gives you the correct exposure for almost anysubject, since once you set your exposure correctly for 18% gray, allthe other reflectance values fall into place. A white subject with90% reflectance reproduces as 90% white. 0% black reproduces as 0%black. 50% gray reproduces as 50% gray. And so on.

INCIDENT LIGHT METERS MEASURELIGHT FALLING ON THE SUBJECT.

Normally, the only time you have to adjust an incident reading iswhen you want to reproduce something darker or lighter than it reallyis. For example, you might want to open up your aperture to lightenand show more detail in a very black face; or close down and darkena very white face to see more detail in it o


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12LENSES

TelephotoorrMl

The human eye is a wonder. With a single lens, it can concen-trate on a tiny detail of a scene, excluding all else, and in thenext instant take in a whole panorama. Unfortunately, the camerais not so versatile. It requires many different lenses t o evenapproximate the performance of the eye.

Every camera has one .lens which is considered the "normal"lens. This is the lens which comes closest to reproducing objectswith the same perspective as the human eye; that is, objects appearto be the same size, proportion and distance as if we weren 'tlooking through the camera at all, but seeing them with the nakedeye. The normal lens usually includes a horizontal area of about25 degrees.

On a sixteen millimeter camera, the normal lens has a focallength (its optical measurement) of 25 millimeters. On a 35-millimeter camera, it's 50 millimeters long. On a video camerawith a 2/3" CCD chip, the normal lens is 25 millimeters long.

The other lenses on the camera are classified "wide angle" ifthey include a larger area that the normal lens, and "telephoto " ifthey include a smaller area.

Wide angle lenses are shorter than normal lenses; telephotolenses are longer. If your normal lens is 25rnm, your wide anglemight be 12rnm and your telephoto 100rnm.


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13characteristicside angle and telephoto lenses have specialwhich can be slDllIDarized as follows:1 ~ 7 ( J + ? U 1Q

W i d e A ~* Includes a larger areathan the normal lens atthe same distance--goodfor cramped quarterswhere you can't move thecamera back any farther.

* Includes a smaller areathan the normal lens atthe same distance--goodfor distant subjectswhere you can't move thecamera closer.* Subject is smaller inthe frame than with thenormal lens at the samedistance.

* Subject is larger inthe frame than with thenormal lens at the samedistance.* Exaggerates depth-makes elements appearfarther apart thannormal.

* Compresses depth--makeselements appear closertogether than normal.* Because of exaggerateddistances, movementstoward and away from thecamera seem faster thannormal. Move 6 inchestoward the camera andit looks like you'removing 18 inches.

* Because of compresseddistances, movementstoward and away from the' camer a seem slower thannormal. Move 18 inchestoward the camera and itlooks like you're moving6 inches.

* Because of smallerimage size, camerajiggles are lessnoticeable. Good forhandholding thecamera.

* Because of larger imagesize, camera jiggles aremore noticeable. Bad forhandholding the camera.


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14and telephoto lenses reproduce faces ln different

NormalWideAntJle

Features becomespread ou t ,bulbous.

ielephotvFeatures becomeflattened o u t ,compressed.

The more extreme wide angle lenses suffer from geometricdistortion. Vertical and horizontal lines become curved near theedges of the frame. This is called pincushioning.

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FOCUS. The healthy human eye normally sees images in focus--thatis, sharp and clear, not blurry. This is because the lens of the eyeautomatically brings each light ray to a sharp point on the lightsensitive surface at the back of the eye. The pattern formed by allthese sharp points of light taken together forms a clear, sharpimage.

Automatic focus cameras, which emulate the eye, don't always workthe way you want them to. When you have the time, it's usually bestto do the focusing yourself.

To focus a camera which doesn't have through-the-Iens viewing ,you measure or estimate the distance of the subject from the camera,then move the focus ring on the lens to that setting .

Focusing is easier, quicker and surer on cameras with throu ghthe-lens viewing systems. This is because there's no guessworkinvolved--what you see is what you get. All you do is look in theviewfinder and turn the focus ring on the lens till you r subject look ssharp and clear. (If possible on a film camera, you should open thelens to its widest aperture for focusing--I'll explain why in thefollowing section on depth of field.)

Some cameras have focusing eyepieces, which use little diopterrings to adjust the focus of the image in the viewfinder to theindividual eye of the cameraperson. Adjustable eyepieces areespecially useful for people who wear glasses but who prefer or needto shoot without them. (It's not a good idea to wear glasses wh enshooting with a through-the-Iens film camera--light entering theviewing system from around the edges of your glasses can fo g the film.)

If your camera has a focusing eyepiece, do adjust it to youreye--otherwise you'll never see a perfectly sharp image throu gh thelens and you'll never be 100% sure of your focus.


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To adjust a focusing eyepiece, first point the camera at abright area--the sky, or a white wall, for example. Open the lensto its widest aperture. Throw the lens out of focus--turn the focusring until everything is as blurry as possible. Then, on a film camera,turn the diopter ring on the eyepiece until the ground glass of theviewfinder screen is in focus--until the textured surface of the screenis as sharp and clear as possible. On a video camera, adjust thediopter ring until the messages on the viewfinder screen are as sharpas possible. That's all there is to it. Now you're ready to focusthe lens with complete confidence.

ZOOMLENSES. Most cameras use a zoom lens, which combines a widerange of focal lengths in a single lens. By moving a single control,you can switch from wide angle to normal to telephoto, or anywhere inbetween, without changing lenses. This makes it a lot easier andquicker to compose your shots. If you want a little wider frame,zoom back to wide angle; for a closer shot, zoom in to telephoto.

There's a special way to focus a zoom lens. First, zoom all theway in on your subject, with the lens in maximum telephoto position.Focus the lens,even if all you see is an eyeball. Then zoom outwide and find your final framing. Your subject will remain sharp andin focus at any zoom setting, as long as neither the camera or thesubject changes position. (When possible on a film tamera, you shouldalso open the lens to its widest aperture for focusing--we'll learnwhy in the following section on depth of field.)


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17DEPTH OF FIELD

Depth of field is simply the area in front of your camerawhere everything looks sharp and in focus. For example, if you'refocused on somebody standing 10 feet in front of the camera, yourdepth of field might be from 8 feet to 14 feet. That means objectsfalling within that area will be acceptably - sharp and in focus;~ b j e c t s falling o u ~ s i d e the area will be soft and out of focus.

OOTOfFaGUS~ t - - I M FOCUS CXJTff


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18The next thing to know is: Your depth of fieZd increases as

you decrease your focaZ Zength. With a wide angle lens, you have amuch deeper area in focus than with a normal lens. T h i ~ is why,when you're shooting in uncontrolled situations with a zoom lensand don't have time to zoom in and check focus, you're better offsetting an approximate focus and staying at wide angle. This willgive you your best chance of keeping everything in acceptable focus.

WIDE ANGLE = GREATER DEPTH OF FIELDAnother thing about depth of field: Your depth of fieZd in-

creases as you cZose down your aperture. At f/16 you have more depthof field than at f/2. When you make your aperture smaller, it'sessentially the same as squinting your eyes to see something sharperin the distance. This is why on film cameras we open the lens toit's widest aperture to focus: it makes it easier to see the exactfocus point.

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riMFocUS,~ < ~ : = ~ ~ ~ - : ~ J f - - - - - - - - - - - -LARGE APERTURE = LESS DEPTH OF FIELD

SMALL APERTURE = GREATER DEPTH OF FIELD


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19Next: Your depth of field increases as your subject gets

farther from the camera. The farther away the subject, the moredepth of field; the closer the subject, the less depth of field.

r - I H f O C U S ~CP------------l- - t ; T I - - - - - . & . - ~ -DISTANT SUBJECT = GREATER DEPTH OF FIELD

~ I ft'GQ1{7?---] _CLOSE SUBJECT = LESS DEPTH OF FIELD

Finally: You always have less depth of field in front of yourpoint of focus than behind it. This is especially noticeable atdistances of 25 feet or less. At these near distances, you canusually figure on your depth of field extending approximately 1/3in front and 2/3 behind your point of focus. So, if you're workingwith a shallow depth of field and you want to take maximum advantageof it, focus on a point 1/3 of the way into the area you want infocus.


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DEfmOFIEL.D.A.,--- ---,I y ~ ?1j. - - - ~ S - - - - - ----

FOCUSING IN THE MIDDLE LEAVES THE FRONT MAN OUT OF FOCUS.

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FOCUSING ON A POINT 1/3 OF THE WAY IN PUTS EVERYBODY IN FOCUS.

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