I have never used a Celestron 300 but I regularly use a Tamron 500/8 and
occasionally use a Sakar 500/8 t-mount and neither of them shows any
vignetting. The microprism may black out but comes back if I move my eye
in relationship to the viewfinder......no problem focusing at all. The
viewfinder gets a bit darker with a 2X converter on the 500 but still quite
useable unless its near dusk. Nothing at all like you describe.
Bruce Kolber
St. Petersburg, FL 33715
USA
----- Original Message -----
From: "Jim Brokaw" <jbrokaw@xxxxxxxxxxx>
To: <olympus@xxxxxxxxxxxxxxx>
Sent: Wednesday, July 11, 2001 11:58 PM
Subject: [OM] mirror lens and #1-7 screen
> 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
> works without any problems... The Olympus 300 is too heavy to pan with the
> motorcycles, but I may have to use it. The 1-7 screen works with the
Olympus
> 500/8.0 mirror, although a slight darkening in the corners is noticable.
It
> would still be usable.
>
> Anyone have knowledge why this screen won't work with the Celestron 300? I
> like the small size of the lens, and it is acceptably sharp for what it
> cost, but the view is dim for focusing on the 'normal' screens. Are there
> other brighter screens that would be better?
> --
>
> Jim Brokaw
> OM-1's, -2's, -4's, (no -3's yet) and no OM-oney...
>
>
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