Re: [ATM] Rating mirrors,understanding seeing

["Jerry" <wa4guu@verizon.net>]

You should be able to split the double double with a 12" on any night clear
enough to find it.

Here in east coast Virginia I have used 1600X with my 12.5" on two nights
over the last 15 years or so. Thaose two nights were in a row. I don't get
out every night so maybe I missed a some chances. Except for those two
exceptional nights more typical "good seeing" nights 600X would be expected
upper limit. And then most nights 300X is pushing it. On poor nights 150X or
so might be the limit. Just can't be more specific because probabilities of
good or excellent seeing conditions can be significantly different at other
locations.

Even with a turned edge you should be able to split Epsilon-Lyrae. I think
you have some other problem. Terrible collimation, vasaline on the eyepiece,
solar filter left in by accident, soldering iron left on inside the
telescope tube or looking through the plume from a smelting smokestack. I
split Epsilon-Lyrae in a Tasco 60 mm refractor. Easily with a decent
eyepiece. 

Jerry


-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
jeff newsom
Sent: Monday, September 12, 2005 5:37 PM
To: atm@atmlist.net
Subject: [ATM] Rating mirrors,understanding seeing

After looking at the pages of several different optical
companies(Royce,Obsidian, Pegasus and so forth to name a few) and the
writings of Mel Bartel, Bob May and others, and articles on optics and texts
on optics(Texerau, Kriege Berry) , I'm still trying to get  a handle on what
magnifications , on average, one  should expect from say, a 12" , f/7 or so
on any given night. Mel seems to be able to push his mirrors consistently to
magnifications well beyond anything else I've seen(1000x)(Where the hell do
you use that thing Mel? In a vacuum?  ;) ). Most "companies "seem to suggest
that 350 to 400x is more the norm as a top end , with magnifications
routinely in the 180,275 range, which is where I seem to be with my most
recent 12" , f/7.3 mirror.
   Now , I understand that "seeing" conditions vary greatly and are a key
component in how far one can push magnification.  Last night, I was able to
split the double -double , Epsilon -Lyrae. But this lasted only a moment
here , a moment there, with a bit of fuzziness(in the star images) present
thoughout. Still , at times, there was a definite break between the
individual components of each double. Now, conditions were obviously not
ideal, with some flickering of stars even near the zenith. I was using a
Siebert 9mm ultra giving me a magnifaction of 245X. My star test reveals a
good figure, but with perhaps a fuzzy edge inside of focus. The mirror has
1/4" off masked already. Will poor seeing create the fuzzy edge inside of
focus? Will a "great" mirror split the double -double  readily in all but
the most marginal of seeing conditions??
   I guess what I'm really after here is where do most of you folks end up
magnification-wise, on average, understanding of course aperture and focal
ratio considerations, local climate , etc......... Thanks---Jeff Newsom
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