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ATM Eyepiece focal plane
Recent postings on the position of the focal plane are very useful. I'm
checking my eyepieces as I read these postings.
I unscrewed the barlow lenses on my Naglers, as well as on my 35 mm
Panoptic to see where the aperure stop was located as a sort of reality
check on these tables. If indeed the aperture stop locates the focal plane
inside the eyepiece, then I believe I get different results than the
tables have presented. Is there some reason for this? Might the stops be
placed in front or back of the focal plane for some reason? I'm assuming
that the flange means the shoulder that sits against the focuser.
Here is what I found (measured in inches) (a positive sign indicates that
the focal plane - or field stop - lies toward the telescope, a negative
sign means towards your
eye).
<html><pre>
Eyepiece Focus to flange My measure of stop to flange
________________ ____________ _____________________
20mm Nagler Type II 0.20 0.0
13mm Nagler Type I 0.20 -0.67
7mm Nagler Type I 0.31 -0.24
4.8mm Nagler Type I 0.31 -0.32
35 Panoptic ? +0.15
</pre></html>
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Chris Westland
Hong Kong University of Science & Technology
Clear Water Bay, Kowloon, HONG KONG
Tel: ++852 2358 7643
Fax: ++852 2358 2421
E-mail: westland@uxmail.ust.hk
WWW: http://home.ust.hk/~westland/westland.htm
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