At 22:17 2/13/01, Robert Gries queried:
does anyone know why most of the zuiko lenes stop down to f16 where most
other manufactures have similar lenses w/ f-22? is it the compact
diameter of the lens?
i'm feeling cheated on my DOF....
This depends on which lens you are discussing. All the 50mm standards only
go to f/16, however the 35/2.8 Shift goes to f/22 and the 300/4.5 to
f/32. All lenses eventually become "diffraction limited" as you stop down,
it's a matter of the aperture f-number when it occurs. Diffraction
limiting has to do with the absolute physical diameter of the aperture
versus the wavelength band of visible light, you cannot escape it and it
degrades the resolving power. With the standard 50mm, this starts to kick
in at about f/16 and I believe Olympus decided to keep lens performance up
versus giving users an extra stop.
Don't feel cheated with your DOF. For a given aperture, focal length and
largest acceptable circle of confusion, you can find the "hyperfocal
distance." If you set critical focus at the hyperfocal distance, the DOF
extends from half the hyperfocal distance to infinity.
The fuzzy part of this is the largest acceptable circle of confusion. What
constitutes acceptable depends on the film format, how much the image will
be enlarged for print or projection, and the intended viewing
distance. For enormous enlargements viewed at close distances, the DOF
shrinks because the maximum circle of confusion diameter must shrink. For
small enlargements viewed at farther distances, the DOF grows because the
maximum circle of confusion can be larger.
-- John
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