Fwd: ATM Star test

["Matthew L. Brown" <mlbrown@everstrive.com>]

The view won't get any sharper with coating, just brighter.  So planets and 
the moon are great targets for an uncoated mirror.

You've discovered the biggest problem with star testing -- it can be as 
much of an atmospheric test as an optics test, and in most places, winter 
time = turbulent atmospheres.  Sometimes, if you are patient, there will be 
a moment free of turbulence, and you can get a glimpse of a stationary 
star. It is usually calmer right before dawn.

And, if you don't have a clock drive or equivalent, it helps to use a star 
nearer the pole (e.g. Polaris), so you can use high magnitude without the 
fuss of following the star as well.

Another thing to try is to split a close double near the theoretical limit 
for your mirror.

But I suspect that many of us have not bothered to wait for good enough 
seeing to do a star test and just trusted the benchtop tests.

=Matt


>Delivered-To: mlbrown@0
>From: "Art" <mock47@accessbee.com>
>To: "Atm" <atm@shore.net>
>Subject: ATM Star test
>Date: Wed, 21 Jan 2004 22:07:32 -0800
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>Reply-To: "Art" <mock47@accessbee.com>
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>
>Hi,
>I attempted to star test my freshly polished first mirror 10", F/7.  I think
>there was too much air turbulence as the stars I looked at seemed to scatter
>their light with no evidence of rings.  I could, however, focus in and bring
>the light to a fairly sharp point.  Racking in and out merely created a lot
>of flaring and jumping around. I chose another bright light and found myself
>looking at Saturn.  With a 9mm eyepiece Saturn was sharp and quite round and
>I could clearly see the space between the rings and the sides of the planet.
>I was surprised to get this clear view with an uncoated mirror. Does this
>hold promise of a good figure or is it common?
>
>Art