Chapter 3 Digital Cameras
Lens • Focal length • Measured in millimeters (mm), e.g. 35mm, 50mm • The longer the focal length, the more magnification of the scene. 100mm 300mm
Fixed Lenses • Compact digital cameras have fixed lenses Optical Zoom Digital Zoom
Interchangeable Lenses • Digital single lens reflex (SLR) cameras have interchangeable lenses.
Lens Speed • A fast lens has a large maximum aperture. • A slow lens has a relatively small aperture. • A fast lens is normally more expensive. 200mm f2.0
LCD displays • Most digital cameras have built-in LCD displays. • The LCD display of a digital camera allows the user to preview digital images taken. • Some digital cameras also use their built-in LCD displays as electronic viewfinders.
LCD Displays • Advantages • Instant review • Movable LCD viewfinders extend camera-holding positions. • Disadvantages • Consume battery power • Some LCD displays are not bright enough for outdoors • Limited resolution and inaccurate colors could show misleading previews LCD panel production
Optical Viewfinders • Advantage • Help save battery power • Disadvantages • On most compact digital cameras, optical viewfinders are separated from the lens and do not align with the sensor. (Worse for macro). • On most digital SLRs, optical viewfinders show a slightly “cropped” view of what the image sensor would receive. Optical viewfinder Sensor
The Shutter • Pushing the shutter button of a digital camera involves: • Charging the sensor • Activate the storage media • Meter for exposure and white balance • Auto focus • Etc. • Problem: Shutter lag • Solution: Half-press shutter button to pre-meter, and pre-focus.
Storage Media • Common types • CompactFlash (most common, biggest in size) • Microdrive (biggest capacity, most economical) • SmartMedia (getting obsolete) • Memory Stick (Sony) • xD-Picture (Fuji, Olympus) • Multimedia Card (MMC) / Secure Digital (SD) • Latest trend, smaller size • Mini-SD, RS-MMC, Memory Stick Duo
Flash • Built-in flash • Main problem – too close to the lens in most compact digital cameras; tend to cause overexposure and red eyes • External flash • Some compact cameras also have sockets (hot-shoes) for external flash units – useful
Image Sensor • A image sensor device is actually composed of millions of tiny light-sensitive sensors • When light hits the device, different sensors receive different amount of light • Each sensor converts the amount of light it receives into a corresponding electrical charge • Every electrical charge is then measured and recorded as a number (analog-to-digital conversion) • This is how an image is “digitized”.
Bit Depth • An image is recorded digitally as a matrix of numbers. • Bit depth affects the possible range of each of these numbers. • E.g. 8 bits support 0-255; 12 bits support 0-4095 • Higher bit depth supports “finer” image tone.
Blooming • When the amount of light exceeds the capacity of a sensor, the electrical charge could overflow or leak to adjacent sensors • Blooming occurs with high contrast scenes
Noise • Unlike film grain • Digital camera noise caused by • Electronic interference • Various components of the digital camera could interfere the electrical charges on the image sensor • Heat is a major cause
CCD vs. CMOS Sensors • Charged Coupled Device • Complementary Metal Oxide Semiconductor • CCD sensors used to have better image quality and higher dynamic range in the past. • CMOS sensors have improved a lot and are being used in high-end professional digital cameras. See this link, link,
Physical Dimensions of Sensors • Currently, image sensors come in different dimensions, e.g. • Canon 1Ds Mk II – 36mm x 24mm • Nikon D2X – 23.7mm x 15.7mm • Sony DSC-F828 – 8.8mm x 6.6mm • Canon A100 – 4.5mm x 3.4 mm • Compared with 35mm film: • 36mm x 24mm
Sensor Filters • Each sensor only captures the intensity of light, but not its color – “color-blind” • Each sensor actually has a colored filter in front of it – each sensor only sees one color • Red, green, and blue filters are arranged in some pattern to cover all sensors on a sensor device, • e.g. the Bayer pattern
Color Interpolation • A particular sensor only knows the intensity of one primary color; it guesses the intensities of the other two primary colors based on adjacent sensors’ readings • Could lead to inaccurate colors, undesirable patterns
Dynamic Range • The ability of a sensor device to capture the full tonal detail of an image from highlights to shadows. The SuperCCD SR sensor device with extended dynamic range Olympus Full Frame Transfer CCD