digital photography i
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Presentation on digital photography I gave in 2005 at the Saratoga Library.TRANSCRIPT
- Digital Photography I The Basics Peter Liu Photography kaiscapes .com
- Photography
- From two Greek words meaning drawing with light:
- phos ("light")
- graphis ("stylus", "paintbrush")
- Merriam-Webster:
- The art or process of producing images on a sensitized surface (as a film) by the action of radiant energy and especially light.
- Photography
- The art of capturing light as it falls on a subject or scene, and rendering it so that your viewer is moved by the result.
- Capturing Light
- Hard Light high contrast, well-defined shadows
- Capturing Light
- Soft Light diffused, rich colors
- Capturing Light
- Overhead Light harsh shadows
- Capturing Light
- Front Light flat, lacks dimension
- Capturing Light
- Side Light evokes mood, accentuates shapes
- Capturing Light
- Back Light may need to fill, makes silhouettes
- Capturing Light
- Overcast Light low contrast, muted shadows, good for detail
- Characteristics Of Light
- Quality
- The smaller the light source, the harder the light appears
- The larger the light source, the softer the light appears
- Direction
- Determines where shadows fall
- Contrast
- Difference between the lightest and darkest tones of the subject or image
- Source
- Ambient daylight, tungsten, flourescent, firelight
- Artificial flash, tungsten
- Intensity
- Reflectance
- Reflectivity of the subject
- Intensity of the light source
- Angle of view
- Distance of light source
- Fall-off
- Increase distance, decrease light level (Inverse Square Law)
- Characteristics Of Light
- Color
- Mixture of primary colors: Red, Green and Blue varies according to source
- Warm predominantly red
- Cool predominantly blue
- Expressed in Kelvin (K):
- Incandescent ~ 3000K
- Fluorescent ~ 4100K
- Flash ~ 5400K
- Daylight
- Direct Sunlight ~ 5200K
- Cloudy ~ 6000K
- Shade ~ 8000K
- Referred to as White Balance in digital photography.
- White Balance 4100K ( Fluorescent ) 3000K ( Incandescent ) 5200K ( Sunlight ) 8000K ( Shade ) 5400K ( Flash ) 6000K ( Cloudy )
- Why Are You Telling Us All This??
- Because good photography depends on being able to execute two things well:
- Exposure
- Composition
- Exposure
- A combination of three factors sometimes known as the Photographic Triangle:
- Shutter Speed
- Aperture
- ISO
- Or
- how quickly light is being captured through how big an opening onto how sensitive a surface
- Shutter
- A cameras shutter covers the hole through which light enters to expose the sensor or film.
- Shutter Speed Fast
- 1/1600 sec., stops action
- Shutter Speed Slow
- Silky, cool, edgy effects
- Shutter Speeds
- Open too long, photos are washed out (overexposed)
- Not long enough, photos are too dark (underexposed)
- Expressed in seconds: 1/8000, 1/4000, 1/2000 1/1000, 1/500, 1/250, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, 1 second, 2 seconds, etc.
- Each setting is half or double the speed of its neighbor.
- As the amount of available light decreases by half, the shutter speed needs to slow by double.
- As the amount of available light increases, the shutter speed needs to increase
- Aperture
- The opening through which light enters the camera.
- Aperture
- The size of the opening is expressed as an f-stop number : 1.42.02.845.68111622
- Each number represents an opening size that is half or double its neighbor
- The larger the number, the smaller the opening
- For all the science types: the f-stop is actually a ratio between the diameter of the aperture in the lens and the focal length of the lens:
- e.g. f/2 on a 50mm lens says the aperture is 25mm. 50/25 = 2.
- (Source: A Tedious Explanation of the f/stop by Matthew Cole)
- For the rest of us: the size of the opening controls the depth of field in the photograph.
- Aperture And Depth Of Field
- f/5.6
- Shallow depth of field
- Aperture And Depth Of Field
- Caused by refraction of the light hitting the edge of the opening
- Rays scatter and overlap instead of going straight on its way to the sensor or film
- The camera sees multiple images, resulting in blur.
- The smaller the opening, the less surface available to scatter the light, resulting in less blur.
- Bottom line: the aperture is used to control how much of the scene is in focus.
- Aperture And Shutter Speed
- The following reciprocals will yield the same exposure:
- What changes is how much is sharp and in focus.
- The Light Meter
- A device that assesses a scene and figures out the correct exposure
- Modern cameras have them built-in
- External handheld models also available
- Engaged when shutter is pressed halfway
- Matrix/Evaluative, Center-weighted, Spot metering
- Looks for 18% Grey or Middle Grey
- Easily fooled!
- Tricky Metering Situations
- Exposure Compensation
- Used when the light meter is unable to evaluate the exposure as desired, or when correcting by whole stops is too much
- Usually +/- 2 EV (Exposure Value) in steps of 0.3 EV
- Available on most cameras
- ISO
- Sensitivity of the sensor or film to light
- Represented by a number assigned by the International Standards Organization (hence, ISO) 100, 200, 400, 800, etc.
- Again, each number represents double or half the sensitivity of its neighbor (Aint it wonderful!)
- The higher the number, the more sensitive to light
- Digital photography is cool because you can change the ISO from shot to shot!
- Higher ISO = More Noise!
- ISO 3200
- So
- Exposure depends on:
- Shutter Speed how fast
- Aperture how much
- ISO how sensitive
- And color is a function of:
- White Balance how hot
- And
- Which camera you choose is a function of how much you want control those factors!
- Cameras
- Two popular types of cameras on the market for the consumer
- Cameras
- Point-and-shoot
- Viewfinder separate from lens
- Small and compact
- Fixed lens
- Shutter delay
- Usually fully automatic (some exceptions, like Olympus C-series)
- SLR (Single-lens Reflex)
- Based on 35mm design
- Actual image seen in viewfinder
- Interchangeable lenses (more flexible composition)
- Ability to use filters
- More advanced metering and shutter system
- Little to no shutter delay
- Automatic, Program (Scene), Shutter Priority, Aperture Priority and Manual modes
- Flash hot shoe
- Pro models may not have pop-up flash or Program (scene) modes
- Point-and-shoot Anatomy
- Viewfinder separate from lens (better to use LCD on digital)
- Actual image (as exposed) is not quite the same as in the viewfinder
- Much simpler design than SLRs.
- SLR Anatomy
- Through-the-lens (TTL) viewing (works like a periscope)
- Actual image (as exposed) is shown in the viewfinder
- Mirror flips up when the shutter release is pressed, exposing the sensor (and blacking out the viewfinder)
- Reflex
