Digital Sensor Size
SENSORS IN DIGITAL PHOTOGRAPHY
Most digital cameras, even many digital SLR's, have sensors that cover a smaller area than 35 mm film. These smaller sensors have a number of effects on the captured image and the use of the camera.
1. Decreased light sensitivity and increased pixel noise
2. Increased degree of enlargement
3. Decreased depth of field
4. For digital SLRs, cropping of the field of view when using lenses from a 35 mm camera
Light sensitivity and pixel noise are both related to pixel size, which is in turn related to sensor size and resolution. As the resolution of sensors increase, the size of the individual pixels has to decrease. This smaller pixel size means that each one collects less light and the resulting signal is amplified more to produce the final value. This amplification also includes an amount of noise in the signal. With a smaller signal, the signal-to-noise ratio increases. Not only is more noise added to the image, but the raised noise floor means that less useful information can be extracted from the darker parts of the image.
The depth of field of a camera/lens combination increases as the film/sensor size decreases. This is arguably an advantage for compact digital cameras since they are intended for taking snapshots. It means that the scene will be more in focus than with a larger sensor, and the autofocus system does not need to be as accurate to capture an acceptable image. However, depth of field is often used in more artistic fields of photography, for example to isolate a subject (in focus) from the background or foreground (out of focus). When using a digital camera with a small sensor, the photographer would have to use a larger aperture on the lens to achieve similar amounts of "bokeh".
Most digital SLR's use lens mounts compatible with lenses intended for film cameras, commonly 35 mm. If the camera has a smaller sensor than the intended film frame, the field of view of the lens is cropped. This crop factor is often called "focal length multiplier" since the effect can be simplified to that of multiplying the focal length of the lens.
Only some digital SLR's have so-called "full-frame" sensors — a sensor with the same size as a 35 mm film frame (36 × 24 mm). These larger sensors eliminate the issues with depth of field and crop factor when compared to 35 mm film cameras, whilst alleviating the problem with pixel noise and sensitivity by allowing larger pixels.
Convenience and Flexibility
Digital photography is flexible to the extreme; a photographer can change anything about a photograph after it has been taken.
This has been one of the major drivers of the widespread adoption of digital cameras. Before the advent of digital cameras, once a photograph was taken, the roll of film would need to be finished and sent off to a lab to be developed. Only once the film was returned was it possible to see the photograph. However, most digital cameras incorporate an LCD screen which allows the photograph to be viewed immediately after it has been taken. This allows the photographer to delete unrequired photographs and offers an immediate opportunity to re-take. When a user desires prints, it is only necessary to print the good photographs.
Another major advantage of digital technology is that photographs can be conveniently moved to a personal computer for modification. Many professional-grade digital cameras are capable of storing pictures in a Camera RAW format which stores the output from the sensor directly rather than processing it immediately to an image. When edited in suitable software, such as Adobe Photoshop or dcraw, the photographer can manipulate certain parameters of the taken photograph (such as contrast, sharpness or color balance) before it is "developed" into a final image. Less sophisticated users may choose to simply "touch up" the actual content of the recorded image; software with which to do this is often provided with consumer-grade cameras. (See Digital image editing.)
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