I have a question about the 1-12 screen. It is always described as a cross
hair on a clear field but if you look closely the field is not clear. The
field is actually a fresnel lens pattern. The central circular region that
contains the cross hairs is indeed clear but the rest of the field is made up
of fine concentric circles. At least this is true for any of the 1-12 screens
that I have seen. I use this screen for high resolution solar photography
(a focal length of about 14 meters at f/140) and at this focal ratio the
fresnel pattern is useless. The field outside the clear circle shows up as
concentric light and dark rings.
Does anyone know of a true clear screen with cross hairs? Alternatively,
does anyone have any experience with the 1-11 screen (cross hair with matte
outside the central circle).
Art
P.S. If anyone has a 1-11 in excellent condition, I'd be interested in
hearing your price.
--------------------------------------------------------------------------------
Art Whipple
AGCS, HST MOSES Systems Management
Email: whipple.art@xxxxxxxxxxxxxxxxxxx
Office Phone: 301-901-6058
Pager: 301-220-6252
Alphanumeric paging: 3014744657.0056896@xxxxxxxxxxx
Fax: 301-901-6122
Home Phone: 410-286-2930
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