Raimo wrote, in describing use of the Hoya HMC on the FA 24-90:
[snip...]
> no vignetting (which is a fancy word for light falloff)....
Hi Raimo,
Just a technical point here. Vignetting results because some optical
element (for instance, a thick filter on a wide lens) acts as an aperture
stop, and the image of this stop at the film plane is actually smaller than
the film plane. A typical example of vignetting can be seen when one uses a
medium-format camera coupled to a small refracting telescope in
astrophotography. The optical tube of the telescope acts as an aperture
stop, and if the tube is too small, one sees a circular image in the center
of the emulsion surrounded by a large unexposed area. Light fall-off occurs
as a natural consequence of using a spherical lens to project an image onto
a flat film plane. These are actually two very different things.
Bill Peifer
Rochester, NY
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