 BetterPhoto Member |
Depth of Field If using a 90mm lens, what focus point will achieve the smallest depth of field?
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John P. Sandstedt |
Depth of ield doesn't depend on focus point, rather it's an optical property of the lens related to aperture. Take a lens, any lens and set it to its widest opening [i.e. smallest numerical f/stop.]
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Jon Close |
I beg to differ. Depth of field is directly related to focus distance as well as aperture. The closer the focus the shallower the DoF.
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Alan N. Marcus |
Jon as always is right on target. I tend to be more longwinded. Depth-of-field is that expanse between the nearest and furthest that can be judged to be acceptably sharp. Setting the lens to the widest aperture (smallest f/number) gives the least span. Setting the lens to the tiniest aperture (highest f/number) gives the most. Short focal lengths produce greater depth-of-filed. Conversely, longer focal lengths yield less depth-of-field. Depth-of-field becomes less when shooting close-up pictures. Alan Marcus
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John P. Sandstedt |
Jon, Alan - DOF is a mathematically calculable property of a lens, set at any focal length. The equations appear in Allan Sussman's Handbook of Photogrpahy and many of Andreas Feininger's fine treatises.
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Jon Close |
Yep. And focus distance (subject to lens node 1) is as necessary an input to those equations as is focal length and aperture. DOF cannot be calculated without it.
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