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Posted by Robert May on June 17, 2003 18:26:40 UTC

The proper place to be doing that inspection is at the focal plane. This can be found easily by pointing the scope at something bright and using a ground glass screen or a piece of oiled paper (a little oil on a piece of thin paper will make it a lot more transparent - water tends to make the paper fall apart easily). Do this on the moon rather than on the sun as the paper may ignite from the sun's rays if you don't reduce the light by a lot.
The secondary really needs to only see the full primary near the center for a planetary scope while a wide-field scope will more want to see the full primary to a .5" radius for a 1.25" forcuser for the best viewing.
NEWT2.5 will give all kind of interesting results for different sized secondaries. The nicest thing about the program is that it will also calculate the diameters and spacing for baffles which will make the scope even better performing.

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