On 14 Nov 2003 22:52:33 -0800, (David Knisely) wrote:

Alan W. Craft wrote in message . ..
On 14 Nov 2003 17:33:10 GMT, (Don Martin fan) wrote:

Plan on having a 2" focuser and a Paracorr.

My new Klee barlow is a magic coma eraser!

Should be great then....
Clear, Dark, Steady Skies!
(And considerate neighbors!!!)

Alan

I'm sorry, but your Klee will have little if any effect on coma
created by a paraboloidal primary mirror.

I know that, I KNOW THAT.

I just wanted to say it, and for its shock value.

It appears to have worked...

blows upon fingertips

Though not without realising that I did so irresponsibly,
as I do have a conscience, albeit mischievous. I'll
try to restrain myself in future.

If it did, a Klee Barlow
would cause a reverse sort of coma on telescopes which do not have
much coma, such as some refractors. The Klee increases the effective
focal length of the instrument and thus can sometimes reduce the
problems which some less-expensive eyepieces show when used at very
short f/ratios. The most notable of these problems is off-axis
astigmatism. It is produced by less complex eyepieces being used in
shorter f/ratio (under f/7) telescopes, and is often mistaken for coma
by inexperienced amateurs. The only practical way of dealing with
off-axis coma in a Newtonian is via the use of coma corrector (such as
the TeleVue Paracorr) positioned ahead of the eyepiece. This will
reduce the coma, but will do little for any astigmatism produced by
the eyepiece. To deal with off-axis astigmatism, you either need a
longer focal length instrument or a more complex eyepiece design such
as the Panoptics or Naglers. Clear skies to you.

Well, there goes my idea for a wide range of Kellners.

I don't think it'll be as bad as that would seem to suggest, however.

David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

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* July 18-23, 2004, Merritt Reservoir *
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eyes the bulk of David's post, hungrily

Very well, I won't snip it, lest a newbie were to be misinformed.

Alan