Depth-of-field Control

The lenses typically used on DSLRs have a wider range of apertures available to them, ranging from as large as f/1.0 to about f/32. Lenses for digicams rarely have true available aperture sizes much larger than f/2.8 or much smaller than f/5.6.

The f/5.6 limitation is because lens designs of typical small sensor digicams already produce diffraction blur bigger than a few pixels at f/5.6. Because of digicams' smaller sensors there are a limited number of apertures available that will produce an acceptably sharp image. Many digicams only have a two-stop range of apertures because at settings outside of these the image will become too soft because of limits of lens design at large apertures, or diffraction at smaller apertures. To help extend the exposure range, some digicams will also incorporate an ND filter pack into the aperture mechanism.

The apertures that digicams have available give much more depth of field than equivalent angles of view on a DSLR. For example a 6 mm lens on a 2/3" sensor digicam has a field of view similar to a 24 mm lens on a 35 mm camera. At an aperture of f/2.8 the digicam (assuming a crop factor of 4) has a similar depth of field to that 35 mm camera set to f/11 – that's a four-stop difference. Put another way, with both cameras at f/2.8 and focused on a subject 1 meter from the camera, and both cameras zoomed to produce the same angle of view (35 mm camera will need to use larger focal length to produce same angle of view from same distance), the digicam might have a depth of field of 2 meters and the larger camera would have a depth of field of 0.3 meters.