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Friday, January 28, 2011

Depth of Field calculator

Most photographers know the effect of different apertures. The smaller aperture (=bigger f-value) the longer depth of field. But how long is the depth of field precisely?

I was quite surprised how much the distance from the subject affects the length of the depth of field. Let's imagine that we are taking a photo of a flower from one meter distance with 100mm f2.8 on 1.6 crop frame. Based on an online calculator the depth of field is 9.7 mm. But we want to double that because the flower is not completely sharp.

Stepping down to f5.6 gives depth of field of 19.3 mm. Now the dof is twice as long but the exposure time has become four times longer. In case of hand held photography this might be too much.

Another option is to keep aperture at f2.8 but take one step backwards so that the distance is 1.4 meters.  This will give the same depth of field as above but without the expense of longer exposure time.

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