Winsor Crosby wrote:
> There are two kinds of diffraction operating, the one from the small
> physical size of the aperture and the one from the small size of the
> photosensor site. On a D2X which has photosites on the sensor almost
> identical in size to the ones on your E300, F11 is just beginning to
> show softening. F11 is probably a good limit for your camera too, but
> a little sharper probably with a half stop wider.
>
Aperture associated diffraction depends a lot on the focal length of the
lens. F-stop is not an absolute, but a ratio equal to the focal length
divided by the clear aperture. Thus the actual physical size of the
aperture opening, which is all that matters for aperture derived
diffraction varies considerably with focal length.
FL aperture
mm f-stop dia. in mm.
300 11 27.3
150 11 13.6
75 11 6.8
50 11 4.5
24 11 2.2
12 11 1.1
I don't remember all that stuff that determines at what diameter
aperture diffraction becomes a problem, but the above table clearly
covers a range from no trouble through considerable trouble.
Diffraction from light passing through a small opening without a lens
becomes very high as the size of the hole gets small. That's how pinhole
'lenses' work.
Moose
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