RE: filmscanners: NIKON LS 4000 AND D1X

["Shough, Dean" <dean.shough@lmco.com>]

> There is one good thing about that tough. The CCD require that the rays
> come in at 90 degrees. Especially with a wide angle lens the exposure
> rate would depend on the distance from the middle point. I have to
> admit that I don't know how bad that effect is, though. Also I believe
> that lens design can compensate for it somehow. And if not you can
> still do it electronically. Assuming that the most important object is
> somewhere around the middle that shouldn't be too bad.
>

I believe you are referring to the cosine to the fourth power falloff of
light with angle of incidence.  The classic method of compensating for this
effect is to place a gradated neutral density filter near the leaf shutter
on a view camera.  Modern 35 mm lenses compensate for the fall off by using
pupil distortion.  Look through the back of a wide angle 35 mm lens.  Rotate
the lens and look at what happens to the apparent size of the aperture.
Near the edge of the field of view the aperture appears to increase in size,
letting more light through the lens.  With older lenses the aperture gets
smaller as you increase the angle of incidence - contributing to the
cosine^4 falloff.