I guess it depends partly on the lens. Maybe it has to do with the the
'obstruction ratio' you mentioned. The Tamron 500/8 is 78mm aperture
with 35mm obstruction = 45%(240f area) while the Meade is 84/29mm =
35%(120f area).
I was recently using my Meade 1000/11 with the all-matte Beattie and
tried substuiting the 1-7 screen. The microprism was not darkened.
Neither one was really easy to focus - no depth of field to speak of,
but neither was obviously easier to focus than the other. I was wokring
in good light, but I'm sure the 1-7 would be better in dim light, at
least you could see the subject. Neither the Beattie or the 2-13 is very
bright at f11.
Moose
Carlos J. Santisteban Salinas wrote:
The 1-7 works OK with a small, _unobstructed_ aperture, like that on the
1000/11. The central obstruction in a mirror lens will darken the
microprisms, despite the larger aperture. However, the all-matte Beattie
(or the 2-4 screen) should be fine.
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