P3D Optimum sharpness

["OLE HANSEN" <olejohan@xxxxxxxxxx>]

Kenneth Luker <KLUKER@xxxxxxxxxxxxxxxxxxxxxxx>wrote:
> ....sometimes a smaller aperture is detrimental to sharpness,
> due to diffraction. Can someone explain how one can see the
> difference between un-sharpness due to wide aperture (loss of
> depth of field) and un-sharpness due to TOO SMALL an aperture
> which has caused diffraction? How do these differ in appearance....
They do not differ in appearance. The circle of distortion in the
focal plane is just increasing when smaller and bigger apartures
than the optimal is used.

> ....and how can one determine the optimum f-stop?
You can try to get hold of the manufactures datacard for the lens,
or you can test the lens yourself with a testcard, a slow black
and white film and a microscope with 100 x magnification.
One exposure for each f stop should give you a good idea of the
definitioncurve of the lens. Paterson has made a useable testcard.

> If a 3-d view has diffraction-caused fuzziness, can one see a
> place in the view where that fuzziness begins, or is it present
> throughout the view?
The fuzziness is "all over" the image, and the depth of field
fuzziness is added to the diffraction-caused  fuzziness in the
focal plane.
regards
Ole Hansen - olejohan@xxxxxxxxxx


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