FreeLists / az-observing / [AZ-Observing] Re: Report on the Televue Diagonal

[Brian Skiff <bas@xxxxxxxxxx>]

>>  I was expecting to see an obvious difference in the brightness of the
>>  image between the two diagonals because...
>>  ..increased reflectivity (the 99% reflectivity...

     The difference in nominal reflectivity is only 10-15% at most,
which without having some sort of blinking arrangement, you simply
aren't going to see visually, particularly at low power (the 35mm
eyepiece you mention).  The eye really sucks when dealing with
brightness differences.  Where the newer types of coating ought to
help is with increased contrast---less scattered light, which should
be noticeable in crowded fields, being able to see stuff better   
on planets etc, all at high power.

     The problem you with the variation in image-quality across the
field with the Meade diagonal is probably a squaring-on issue either
in the machining or with how the mirror is mounted (or both).
That's why you pay more for the one that's right (literally right-angled),
and where every piece has been checked before being sent out.


\Brian
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