depth of field

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does depth of field work the same in digital cameras as it does in film cameras? for example, does opening up the apperture (say to f2.8) decrease the depth of field? Or is there really any difference in a digital camera? i have an olympus 3030 and haven't yet seen any appreciable difference in different f stops. is this just me or is it a construct of all digital cameras?

thx

-- alex morrison (alexm@epi.ca), May 23, 2000

Answers

I found a pretty decent answer to your question on the Olympus product comments portion of the forum. It is copied below. Joe

IR review of this camera is really fine. F-stops limited to two, full and a second stopped-down aperture would seem a limitation, however, the actual lens opening in such a short focal length lens as used in a digital camera means the depth of field will be great. Dept of field is proportional to the lens opening, not the f- stop. This means any lens set to a given diameter opening has the same depth of field. A 35 mm lens (typical 35mm camera wideangle lens) set at f7 will have a 5 mm iris opening, and a good depth of field from about 10 ft to infinity (?) Most of us would like to stop the lens down further to f11 at least to get more depth of field. But a 10 mm lens, typical of wideangle digital camera lenses, at f7 will have a 1.5 mm iris opening, equal to more than f 16 on the 35 mm lens, and this will mean quite a large depth of field, say 3 or 4 ft to infinity. The main issue is reducing, not increasing depth of field. True, it does limit the shutter priority work one could want, since you only have two responses to light and shutter speed.

-- Joe Peterson (jwpeterson@aol.com), May 23, 2000.


The depth-of-field issue isn't down to digital cameras as such, just the stupidly small size of the CCD sensors that are fitted to them, and the correspondingly short focal length of the lenses that have to be used. Depth of field increases as format size is decreased. Most amateur digicams have a CCD sensor that's about 1/5th the linear size of a 35mm film frame. This increases the depth of field by 5 times for the same aperture. What this means in practice is that digicams give almost no control over depth-of-field whatsoever. The small CCD size also means that really wide angle lenses just aren't available. At the same time it increases the background noise and diminishes the light sensitivity of the camera. There really is no technically good argument for having a small sensor size, apart from cost.

Kodak'website has details of sensors which are 36mm square and contain 16 million plus pixels.

See here Now that would make a decent digital camera, not the crappy little 6mm x 8mm offcuts of silicon that we're being fobbed off with at the moment.

-- Pete Andrews (p.l.andrews@bham.ac.uk), May 24, 2000.


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