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Re: [OM] mirror lens and #1-7 screen

Subject: Re: [OM] mirror lens and #1-7 screen
From: "O.C" <oben@xxxxxxxxx>
Date: Thu, 12 Jul 2001 23:40:29 +1000
This happens even with Zuikos. I know that when I owned a 50mm f3.5... I was shocked to find that it had the same described behaviour with a 1-5 screen. It seemed strange that this lens should not be compatible with the 1-5 and yet a 50mm f1.8 was. Obviously has to do with something I'm not aware of.

Oben



At 11:29 PM Thursday 12/07/2001, you wrote:
>
> > I bought a Celestron 300/5.6 mirror lens because it is very compact. A
> > T-mount, but since it doesn't change aperture anyway this is fine.
> Realizing
> > that the 5.6 aperture is likely to be dim I got a #1-7 screen, which is
> for
> > telephoto and slow lenses. I put this screen in my OM-4 to use at a
> > motorcycle race with the 300...
> >
> > With the 300 mirror lens, the viewfinder is almost unusable. The image is
> > severely vignetted, resulting in a circular image about 1/3 of the screen
> > width only in the middle of the finder. The microprisms are blacked out,
> and
> > the fresnel is very visible.
> >
> > I tried the 1-7 screen in the OM-4 with my Olympus 300/4.5 lens, and it
>

Wonder if this could have anything to do with the large secondary obstruction
a F5.6 Catadioptric lens has???

Mark Hammons



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Dr. Oben O. Candemir MBBS Syd Uni.



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