On 26 Jan 1999 14:28:13 GMT, in rec.photo.equipment.35mm you wrote:

>George Pang (gsp4@cornell.edu) wrote:
>: Wouldn't what you observe as 'vignetting' more likely be 'light falloff'
>: towards the corners. There is a very distinct difference:
>
>: Vignetting:
>: an actual blocking of light by something (usually in front of the
>: lens) like a filter with a too wide ring.
>: doesn't usually go away with stopping down (It should actually get
>: sharper and more pronounced as the blockage in question is MORE in
>: focus)
>: The image 'data' is lost entirely because it is blocked
>
>: Light-falloff:
>: is a NATURAL consequence of the use of a very wide lens
>: , any 14mm lens on the 35mm format will have the same
>: 'problem'.
>
> Actually, you are confusing simple obstruction,
> or corner cut-off, with vignetting. Vignetting
> is *never* in focus or even close to focus no
> matter how you stop down, and is more akin to
> fall-of than to cut-off.
>
> Corner cut-off is a projection into the field of
> view that literally hides the corner. Fall-off
> is just the inescapable result of increasingly
> oblique projection angle as the image is painted
> out to the corner. Vignetting is the reduction
> in visible area of the exit pupil, and is most
> definitely improved by stopping down, so as not
> to be using the part of the image of the iris
> that has been compromised.
>
> Regards, - dr
golem@shell.acmenet.net (David Rozen)