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[OM] Re: Vignetting on digital 50-200

Subject: [OM] Re: Vignetting on digital 50-200
From: "Jeff Keller" <jeff-keller@xxxxxxxxxxxxxxxx>
Date: Mon, 21 Mar 2005 16:32:11 -0800
> Barry B. Bean wrote:
>
> >I'm glad you posted that. It was windy when I was shooting, as well
(although there were no 50 knot gusts). Maybe the hood is just a little
longer than it needs to be.
> >
> >
> Hang on a minute. I don't own one of these, but I can say that unless
> the front element moves relative to the hood, vignetting at 83mm would
> just be worse at 50mm, which is not what you report..
>
> As Piers and AG noted, this doesn't look like hood vignetting, but
> subtle light fall-off in the lens design in this focal length range.
>
>
> Moose
>
>
Watching the lens as it is zoomed, it looks like the hood might be effective
at all focal lengths.  The inner elements move towards the front as the lens
is zoomed from 200 to 50. It both feels and looks like they move at a
constant rate (nothing special about 83mm). IRRC lens fall off occurs at cos
**2 or cos**3 with angle from the axis. So the 50 should be worse for lens
fall off & probably one end or the other of the zoom range would be at least
as likely to vignette as the middle.

Looking carefully at BB's picture, to me the lower left does not show the
fall off that the upper two corners show. The lower right corner appears
darker because of the scene. A crooked hood seems like the best guess.

-jeff


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