 Jonathan Travis |
Focusing For Maximum Depth of Field I have been haunted by this question for a long time; could someone help me? Where do I focus for maximum Depth of Field and sharpness while using the smallest aperture of my lens? Because some of my images at my smallest aperture look great, Sharp, and on others I can see a lack of distinctness. Thanks,
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Alan N. Marcus |
It is a false assumption to believe that smaller lens opening are the sharpest. In general, the sharpest f stop is about two (2) stops down from the widest opening. In most cases this will be about f 8 or f 5.6. Exactly which f stop is the sharpest varies from lens to lens. As to depth-of-field: The smallest lens aperture gives maximum depth-of-filed however, small openings induce diffraction which degrades the quality of the image. Diffraction is induced as light waves pass close by as obstacle such as the lens aperture. Diffraction is devastating so a lens manufacture restrict how far you can stop down. Depth-of-field is the distance span fore and aft of the actual point of focus that remains in acceptable focus. You can consult tables and markings on lens barrels for detains. Actually this range reduces if you are making large prints and increases if the print is to be small. For me, this simple rule prevails. Depth-of-field extents about 2/3 forwarded and 1/3 behind the point focused upon. Alan Marcus
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Jonathan Travis |
Thanks for the all info. Jon
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Michael H. Cothran |
I believe (but am not 100% certain) that Alan's DOF figures in his last paragraph are backwards. I think that DOF extends about 1/3 in front of the focused subject (ie, between the camera and subject), and 2/3 behind it (from the subject to the background). A google on the subject would probably validate one or the other. Michael H. Cothran
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Alan N. Marcus |
You are correct Michael: I thought that was what I had said. Depth of field is shallow for nearby objects. Alan Marcus
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Christopher A. Vedros |
I did a search anyway (not that I doubted you, Michael) and found THIS very good description of DOF. It has a chart that shows that the 1/3 front - 2/3 back ratio holds for wide angle lenses, but as your focal length increases, it evens out until at 400mm, it is about 50/50. Not that it really matters much, because the DOF is very shallow at long focal lengths, I just thought it was interesting. Chris
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Christopher A. Vedros |
The link didn't work. Try HERE.
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Kerry L. Walker |
http://www.dofmaster.com/dofjs.html
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