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[OM] Re: Vignetting on digital 50-200

Subject: [OM] Re: Vignetting on digital 50-200
From: Moose <olymoose@xxxxxxxxxxxxxxx>
Date: Mon, 21 Mar 2005 15:59:34 -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.

One of the features of the E-1 is the ability of the lens to communicate 
to the camera about its vignetting characteristics, allowing the problem 
to be compensated for. Of course, everybody has this turned off because 
of the huge performance hit, but it is there.  See the dpreview review 
heading "Noise Filter & Lens Shading 
<http://www.dpreview.com/reviews/olympuse1/page10.asp>". Before deciding 
the problem is with hood or lens, try shooting with the Lens Shading set 
to on. I think this may also be available after the fact in RAW processing??

The lens designers undoubtedly assumed that their clever technique of 
compensating for lens issues in firmware gave them a little leeway in 
the vignetting area in the optical design. What they didn't expect was 
that processing would be so slow in the production cameras that it 
wouldn't be used. Maybe the E-3 will have a fast processor.

Moose


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