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Camera Basics

Camera Definitions

  • Film: light-sensitive chemical on plastic backing that records image in film camera
  • Image Sensor: electronic light-sensitive chip that records image in digital camera
  • Lens: optical part of camera that focuses light on the film/sensor
  • Shutter: mechanical or electrical control of how long the film/sensor is exposed to light
  • Exposure: letting light onto the film/sensor to capture an image
  • Exposure range or dynamic range: range of lighting in a scene, from the brightest to the darkest areas
  • Focus: producing a sharp image on the film/sensor by adjusting the lens
  • Depth of focus: range of depth over which objects are in focus.
  • Viewfinder: optical or electronic means of viewing the scene in the camera before taking the picture


  • Speed:
    • Sensitivity of film/sensor to light.
    • Specified as ASA/ISO number
      • Slow: ASA/ISO 100 and lower for daylight
      • Medium: ASA/ISO 200, general purpose
      • Medium-fast: ASA/ISO 400: indoors
      • Fast: ASA/ISO 800 and above: low-light, sports, action
    • Higher speed = more sensitive, more grainy, wider dynamic range, lower contrast
    • Film is made in different speeds
    • Sensor: adjusts speed electronically. Higher speed = more noise
  • Types of film:
    • Color or black and white negative, used mainly for making prints
    • Color or black and white transparency (positive, reversal film), used for direct viewing as slides
    • Instant: produces finished print in seconds after exposure, very expensive per shot, discontinued by Polaroid, still made by Fujifilm.
  • Image Sensors:
    • Sensors convert light into electricity
    • Sensors are a matrix of light-sensitive elements
    • Smallest sensing unit is the pixel
    • Resolution is measured in megapixels (million pixels)
    • Types of sensors:
    • Dust reduction: SLR sensors are exposed to dust when lenses are changed. Automatic dust removal vibrates the sensor or filter in front of sensor to shake off dust.
  • Size:
    • File size measured in width (35 mm), dimensions (4”X5”) or type (110, 120)
    • Larger film = higher resolution, bigger camera, higher cost
    • Digital equivalent is sensor size. Sensors are usually much smaller than film
    • Common digital sensor sizes: full-frame (24X36 mm), APS-C, 4/3", 1/2", 1/3", 1/4"
    • Larger sensors = lower low-light noise
    • Smaller sensors mean deeper depth of field
    • Crop factor: ratio of full-frame 35 mm to sensor width, multiplies effect of focal length of lens
  • Color Balance:
    • Color balance varies with lighting: outdoor (lots of blue), indoor incandescent (lots of red), indoor fluorescent lighting (lots of green)
    • Electronic flash simulates outdoor lighting
    • Film is made for specific lighting conditions, specified as color temperature in degrees Kelvin.
    • Filters can be used to adjust for different lighting, but sacrifice film speed
    • Digital cameras can adjust color balance automatically or can be selected manually
    • Color balance can be adjusted by photo editors
  • Exposure range:
    • Film latitude: range of a film's ability to capture the brightest to darkest areas of a subject and still maintain detail, also how much film can be over or under-exposed and still have acceptable results.
    • Faster film (higher ASA/ISO) tends to have wider latitude.
    • Color negative films has wider latitude than transparency film.
    • Digital equivalent is sensor dynamic range.
    • Larger pixels in digital sensors have wider dynamic range.
    • Special sensor design can increase dynamic range, e.g. Fuji Super CCD
  • Film Form
  • Digital Camera Storage Media
    • Flash memory card
      • Smartmedia: early format, now obsolete, max capacity 128 MB.
      • Compact Flash: largest size, highest capacity, popular in DSLR's.
      • Multimedia Card (MMC): predecessor of SD.
      • Secure Digital (SD): most popular format for compact cameras, mini-SD and micro-SD are smaller versions.
      • Memory Stick: proprietary format from Sony.
      • XD Picture Card: proprietary format used by Olympus and Fujifilm
    • Micro-drive: 1 inch hard disk drives in compact flash format, now largely superceded by flash memory.
    • Floppy disk: 1.4 MB magnetic diskette, used in early digital cameras, now obsolete.
    • CD-R: writeable compact disks, used in early digital cameras, max capacity ~700 MB.
    • DVD-R: writeable DVD disks, used in digital video cameras, capacity ~4.7 GB.

Lens Focal Length

  • Focal length: distance from lens to focal point (where distant light entering lens converges to a point)
  • Larger focal length = higher magnification
  • Smaller focal length = wider field of view
  • Larger focal length = longer lens
  • Prime lenses have a fixed focal length
  • Zoom lenses have variable focal length. Zoom range = ratio between longest and shortest focal length, not the maximum magnification.
  • Teleconverter can be used to increase the focal length of existing lenses, at the expense of lens speed.
  • Wideangle converter can be used to decrease the focal length of existing lenses.
  • Fisheye lens gives extremely wide angle, but with extreme distortion
  • Macro lens allows extreme close-ups
  • Close-up lens decreases minimum focusing distance of existing lenses
  • Extension tubes/bellows decreases focusing distance of existing lenses
  • For 35 mm:
    • 50 mm is “normal” (what your eye would see)
    • <50 mm is wide angle, good for landscapes
    • >50 mm is telephoto
      • Magnification is focal length / 50, e.g. 100 mm is 2X, 200 mm is 4X
      • 80-100 mm is medium telephoto, good for portraits
      • 135-250 mm is long telephoto, good for sports
      • 300+ is super telephoto, good for wildlife
      • Very long focal length lenses can use mirrors, like a reflecting telescope
      • Longer focal lengths means bigger, longer, heavier, more expensive lens.
  • Lenses for digital cameras are often specified with 35 mm equivalent focal lengths.
  • Magnification depends on film/sensor size, larger film/sensor requires larger focal length for same magnification

Lens Aperture

  • Aperture: size of lens opening (usually controlled by variable-size iris)
  • Specified as f-stop (focal length divided by lens opening diameter)
  • Lower f-stop number = wider lens opening, more light let in to film/sensor, shallower depth of field/focus.
  • Higher f-stop number = smaller lens opening, less light let in to film/sensor, deeper depth of field/focus.
  • Standard f-stops: f/1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22
  • Each successive f-stop step cuts the light by half
  • Lower f-stop requires bigger, heavier, more expensive lens

Shutter Speed

  • Film cameras use mechanical shutters.
  • Digital cameras can use either electronic or mechanical shutters, or both.
  • Shutter speed: how long shutter exposes film to light
  • Measured in fractions of a second, only denominator specified (100 = 1/100th sec)
  • Set shutter speed to stop action, prevent motion blur
  • Faster subject motion requires faster shutter speed
  • Faster shutter speed requires faster film, wider aperture
  • Longer focal length lens requires faster shutter speed to prevent camera motion blur
  • With normal lens, use 1/125th second for hand-held shots.
  • Image stabilization allows slower shutter speeds.

Focus Types

  • Fixed focus: cheapest, lens with small aperture has enough depth of focus so no focusing is necessary, usually used in cellphone cameras.
  • Rangefinder: line up split image in viewfinder, linked to lens
  • Through-the-lens manual: see image through the lens, adjust lens until image looks sharp (used in Single-Lens Reflex = SLR, twin-lens reflex, and view camera)
  • Auto-focus: camera electronically focuses using:
    • Infrared: used mostly in point-and-shoot film cameras, emits 2 infrared beams to illuminate subject to determine distance, works in darkness, may not focus through windows, has limited range.
    • Ultrasound: used mostly in Polaroid instant cameras, bounces ultrasound off subject like sonar to determine distance, works in darkness, will not focus through windows, has limited range, transducer is big.
    • Contrast sensing: used mostly in digital cameras, computer determines focus by adjusting focus until image contrast is maximized, does not work in the dark (unless camera has focus assist light) or on featureless object, can focus through windows.
    • Phase detection: used in SLRs, passes light through separate paths and detects when they are in phase, does not work in the dark (unless camera has focus assist light) or on featureless object, can focus through windows.
  • Auto-focus Zone: part of the image that the auto-focus system focuses on, usually the center of the picture.
  • Feature recognition: camera's computer analyzes the image, looks for features to focus on (e.g. face-recognition).
  • Focus Lock:  freezing the focus on the image in the auto-focus zone, usually by depressing the shutter release halfway, also can lock exposure.

Exposure Control

  • Proper exposure depends on:
    • Amount of light on the subject
    • Light reflected from the subject
    • Film/sensor speed
    • Aperture
    • Shutter speed
  • Sunny f16 rule: In daylight, with aperture at f/16, shutter speed is 1/ISO number. For example, with ISO 100 film, set shutter speed to 1/100th sec. Slight overcast: f/11, overcast (slight shadows): f/8, heavy overcast: f/5.6.
  • Fixed exposure (usually in disposable film cameras): shutter speed and aperture are fixed, camera uses fast film and small aperture to work in wide exposure range.
  • Full manual: set aperture and shutter speed manually, no internal light metering (use exposure tables, separate light meter)
  • Match-needle light meter: adjust aperture/shutter until light meter indicator is centered
  • Aperture-priority: you set aperture, camera sets shutter speed
  • Shutter-speed priority: you set shutter speed, camera sets aperture
  • Programmed: camera picks best combination of aperture and shutter speed.
  • Scene modes: exposure pre-programmed for specific scenes, e.g. fireworks, portraits, sports, landscapes, snow/sand, sunset, etc.
  • Digital camera can also adjust sensor speed
  • Light Metering:
    • Handheld: separate light meter, often used by pros
    • External: light sensor on outside body of camera, usually on inexpensive film cameras
    • Through-the-Lens (TTL): internal light sensor measures light through the main lens, used in SLRs, digital cameras
    • Average metering: measures light over the whole image area, used by external sensors and handheld meters.
    • Spot metering: measures light only from a small area
    • Center-weighted average metering: Measures light from a wide area of the image, but mainly from the center.
    • Matrix/multi-metering: measures light from multiple areas and calculates the correct exposure.
    • Face detection: digital camera's computer recognizes faces, adjusts exposure for the face
  • Exposure tradeoffs:
    • Aperture
      • Wider aperture (lower f-stop) = more exposure
      • Wider aperture = shallower depth of field
    • Shutter speed
      • Slower shutter speed = more exposure
      • Slower shutter speed = more motion blur
    • Film/sensor speed
      • Faster speed = more exposure
      • Faster speed = more grain/noise

Image Stabilization

  • Also called vibration reduction, blur reduction, anti-shake
  • Reduces image blur from hand-holding camera at slow shutter speeds
  • Sensors detect and measure camera motion
  • Optical image stabilization shifts a lens element to compensate for camera motion, built into lens, works with film and digital cameras
  • Sensor shift stabilization shifts the image sensor to compensate for camera motion, works with any lens, for digital cameras only
  • Can improve speed by 2-4 stops
  • Digital image stabilization, electronic vibration reduction, anti-blur increases the sensor sensitivity to allow using a higher shutter speed, at the expense of higher noise
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Created by Ronald Horii 9/14/05, revised 5/26/10