Outdoor Photography & Internet Publishing

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

Film/Sensor

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:

CCD (Charge-Coupled Device): higher quality, lower noise
CMOS/MOS: lower power, cheaper to manufacture
Foveon: higher color resolution

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

Roll in cartridge (e.g. 35 mm, APS, 110, 126)
Roll on spool (e.g. 120, 220)
Sheet (e.g. 4"X5")
Sheets in cartridge (Polaroid instant)

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