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Depth of field in digital cameras

bikerbob 20 198
1 Aug 2002 7:23PM
I have just purchased a Minolta DIMAGE 7i is the depth of field the the same in a digital
camera as it is in a SLR at the same focal length. The Dimage has a 7 x digtal zoom which equates to 28-200mm on a SLR.
J-P 19 396
3 Aug 2002 7:03AM
Digital cameras have a smaller image area than 24x36 so the effective focal legth is longer, however, do not convert back to 35mm equivalence. Look at the actual focal length. DoF is a function of the actual focal length rather than the 35mm equivalent. Medium format and large format cameras have 'less' depth of field - but only if comparing lenses in terms of their angle of view. That is to say a 35mm 645 lens is shallower than its 24x36 equivalent of 21mm. 35mm on a 24x36 should have identical depth of field. Likewise when comparing digital and 35mm. That's the theory anyway.
bikerbob 20 198
9 Aug 2002 1:12PM
Thanks jpdias for your reply. The reason I asked the question was a note in the Minolta manual on the Dimage 7i I quote " For 35mm photographers an aperture range of f/2.8 to f/8 does not seem impressive. However, because of the CCD size and the focal length of the lens, the apertures on this digital camera give significantly more depth of field at any given angle of view with any given aperture than a 35mm camera. So even with the minimum aperture of f/8, the depth of field will give the coverage needed to create beautiful, sharp images." I hpoe this explains why I asked the question.
Derek 21 3
20 Aug 2002 6:39PM
I to am interested in digital v 35mm depth of field and believe the depth of field to be greater on digital. I have not how done any comparisons can one calculate the depth of field?
dynax99uk 20 3
10 Sep 2002 10:57AM
Depth of field is a very complex thing. Basically any lens produces a totally sharp image with zones in front and behind the sharp image which appear to be sharp. Note the word appears to be!!.
The area that appears to be in focus is dependant on the focal length of the lens and the amount by which the image can go out of focus before the human eye can detect it .
A totally sharp image of a point source will reproduce as a point source, a slightly out of focus image will reproduce as a circle(The circle of confusion)

The depth of field on a piece of film or on an image sensor is dependant on the focal length of the lens and the acceptable circle of confusion.

When we make a print we enlarge the image, this will alter the amount that appears in focus as it magnifies the circle of confusion.
Thus the depth of field is less in a large print than a small one.

The same effect takes place between formats
So a 50mm lens on a medium format gives the same depth of field on the film as a 50 mm lens on 35mm film or a 50mm lens on digital.
However the final printed image would undergo different mangification if each was printed to say 7*x5
The medium format would be magnified least and the digital image the most. So the digital image would have the least depth of field and the medium format the most.

The next stage in the process is that the lens focal length is adjusted to suit the film or image sensor size which compensates for the altering mangnification.

A lens of the same focal length as the diagonal of the image is said to be the standard lens.This is where the lens angle of view is used important.
Using a standard lens on the three cameras and then producing identical sized prints will give identical depth of field in the final image.
Daisy_intheMill 18 145 1 United Kingdom
19 Nov 2012 2:41PM

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