Re: [ATM] Using Barlow to reduce Coma

["Mark" <marco.miglionico@btinternet.com>]

to summarise then:

1) I've only avoided coma by looking at a smaller field size (which I could
do with a shorter f.l. eyepiece)

2) The only gain I get is the benefit of longer eye relief from using my
current eyepieces with the barlow, rather than have to
get shorter f.l. eyepieces.

I'll start saving for the Televue then. Or I could sell my car. A bit off
topic but
how come there are 60 billion different eyepieces, reducers, barlows, relays
and filters
from a million different manufactures in billions of tyes of glass/
configuration.......
and only 1 coma corrector???????? (That I can get my hands on in the u.k.!)

Marco Miglionico



>Yes, you'd be looking at a smaller FOV so the coma at the edges will be
>less in terms of it's angle on the sky. However you've >also magnified the
>view. In terms of coma nothing has changed by using the barlow other then
>restricting your FOV. You could >do the same thing just by getting rid of
>the barlow and using a higher power ocular.

>Tony

----- Original Message ----- 
From: "Mark" <marco.miglionico@btinternet.com>
To: "AMT LIST" <atm@atmlist.net>
Sent: Tuesday, January 24, 2006 8:37 PM
Subject: [ATM] Using Barlow to reduce Coma


> Hello all,
>
> A while back I mentioned my acquired F3.3 12in mirror
> which was too fast for my liking. I don't want to go down the 
> coude/nasmith
> route,
> which although are great ideas, i'm going to try grinding a normal mirror
> before
> delving into hyperbolic secondaries.
>
> So my new idea is to remove/reduce coma some other way. I did a search
> on the forum about barlows / coma correctors - no info about using a 
> barlow
> to reduce coma.
>
> What my question really is: will my F3.3 mirror have the same coma as
> an F6.6 newt if I use a x2 Barlow? I phoned SCSastro - a respected u.k.
> eyepiece supplier
> and they informed my this would not reduce the coma to that of an F6.6
> scope. I'm not so sure.
>
> Obviously i've considered remortgaging my house for Televue's coma 
> corrector
> but that option is now out.
>
> Any ideas?
>
> Marco Miglionico
>
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