|Digital cameras are becoming more popular and a number of designs are
on the market. As digital cameras use electronics to capture and store
the image they are not restricted to the traditional camera designs incorporating
film transport mechanisms. Therefore their size and shape often vary greatly.
Digital cameras usually incorporate an LCD (Liquid Crystal Display)
viewing screen that displays the scene viewed through the lens. However
as this process takes power from the battery and the refresh rate of the
viewing system is quite slow an alternative direct viewfinder is often
Digital cameras, in their simplest form, use the principle of lens,
shutter and film as found in traditional cameras. However instead of silver
halide based film, as described in Chemical
Image Processing, the image in digital cameras is usually captured
by a block-array Charged
Coupled Device (CCD) or Complimentary Metal Oxide Semiconductor (CMOS) sensor.
A block-array image sensor is a matrix of light sensitive receptors.
These receptors produce a continuous analogue electrical signal which is
passed through an Analogue to Digital Converter (ADC). The ADC translates
the fluctuations of the sensor into digital signals.
After adjustment and compression the image is usually stored on a removable
storage device, for example Compactflash or Secure Digital.
The image recording mechanism within some digital cameras have variable
speed ratings like silver based films. The normal speed or sensitivity
of the sensor can be increased by an amplification process.
Due to the relatively small size of a block-array sensors a digital
camera's standard lens, as described in Focusing
Light is about 24mm. The standard lens for a 35 mm camera is 50 mm
and significant lens distortion can be introduced with very short focal
length lenses that have not been specifically designed for use with digital
For specialist applications ‘scan backs’ are available for larger format
cameras. These cameras place a scanner type linear array sensor in the
film plane. Although increased resolution can be obtained there is an increase
in time taken to record the image. Therefore ‘scan back’ cameras are only
suitable for still life photography.
|The cutaway diagram on the right of a Sony DSC-S70, introduced in 2000,
shows the typical characteristics of a digital camera. Light enters both
the lens and the viewfinder, behind the lens is the CCD. Images are stored
on a removable memory card, in this case Sony’s proprietary memory stick
on the left of the diagram. The half removed lithium battery powers the
camera for up to 2.5 hours.
For more information please refer to the Digital
Image Processing section.