Re: [ATM] 7 inch sphereical mirror

["David Harbour" <stainless_steel@suddenlink.net>]

Matt wrote this, Dominic.

I know that there would not be any coma with a little spherical mirror; nor 
would astigmatism be an issue, particularly if one were using it only as a 
"telescope", with eyepieces. It ought to do very well; as I related about my 
newbie friend who made a 7" f/10 spherical mirror, and used it, and got 
stunning views with it. I couldn't see anything the matter with the images.

R-101


----- Original Message ----- 
From: "Dominic-Luc Webb" <dlwebb@canit.se>
To: "ATM Superheros" <atm@atmlist.net>
Sent: Monday, April 14, 2008 10:48 AM
Subject: Re: [ATM] 7 inch sphereical mirror


> On Sun, 13 Apr 2008, David Harbour wrote:
>
>> > Perhaps another way of answering this question is to decide over what
>> > field of view one would want a decent visual image.  I may be mistaken,
>> > but won't coma be an issue here?
>> > Matt
>
> Did I miss something? My understanding was that coma is the
> price paid when you make a parabola. Spherical aberration is
> what you get with a sphere. At some point, the trade-off
> between these two defects should be considered. Coma increases
> as one progresses off axis. I think an F/10 can perform very
> well. This scope is in the range of a lensless Schmidt, and
> there are some very impressive images out there of objects like
> Andromeda galaxy covering something like 3 degrees of sky.
>
>
> Dominic
>
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> 


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