Re: [ATM] Using Barlow to reduce Coma

["A. Suijkerbuijk" <a.suykerbuyk@wxs.nl>]

Hi,

I am using a Paracorr on a f/3.2 mirror, but for large magnifications it is 
better not to use it. There is a lot of light around stars, spherical 
aberration perhaps.
It is nice for low magnifications. I think coma is not the main problem, 
field curvature is the real problem.
I think a corrector for high magnifications using such a mirror has to be 
calculated.

Regards,
Adrie Suijkerbuijk
----- Original Message ----- 
From: "Mark" <marco.miglionico@btinternet.com>
To: "Mel Bartels" <mbartels@bbastrodesigns.com>; "'AMT LIST'" 
<atm@atmlist.net>
Sent: Wednesday, January 25, 2006 9:13 PM
Subject: Re: [ATM] Using Barlow to reduce Coma


> O.K., so if I were to pop in a 40mm plossl, then coma would look
> as bad with and without the Barlow?
>
> My common sense tells me that as I am only looking at half the field with
> the barlow in, so
> it would be like looking at the centre area without the barlow -  which 
> has
> less coma!
>
> By that rationale, what I want to know is comarping the smaller field with
> the barlow in the F3.3 scope,
> to say a scope with an F6.6 mirror --   what will the difference be?
> (Bearing in mind I know
> that the Barlowed F3.3 is looking at the central part of the field which 
> has
> inherently less coma.)
>
> Help.
>
> ----- Original Message ----- 
> From: "Mel Bartels" <mbartels@bbastrodesigns.com>
> To: "'AMT LIST'" <atm@atmlist.net>
> Sent: Wednesday, January 25, 2006 4:32 AM
> Subject: Re: [ATM] Using 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?
>>
>> This isn't as easy to answer as one might think since the definition of
>> 'same coma' is fuzzy.  But strictly speaking, no, a Barlow will not
>> decrease
>> or increase coma.
>>
>> Mel Bartels
>>
>>
>> 
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