Re: ATM Offner compensator

["Antonio de Ugarte" <de_ugarte@terra.es>]

These ones are both curved towards the light entrance (the center of
curvature is nearer to the secondary mirror). In the first element the
first surface has a bigger radius of curvature and in the second element
the first surface is the one with smaller radius of curvature.

Antonio

----- Original Message -----
From: <StarHoper@aol.com>
To: <de_ugarte@terra.es>; <atm@shore.net>
Sent: Wednesday, September 18, 2002 11:54 PM
Subject: Re: ATM Offner compensator


> Antonio,
>
> Funny you mention this as I was just reading up on correctors for
> Ritchey-Chretien.
>
> Let me see if I have this correct...
> The correctors I read about had a negative overall effect (similar to a
> barlow) as to compensate the slightly positive nature of the R-C optical
> system. The correctors could have been to reduce Astigmatism and Field
> Curvature, which is very prevalent in a R-C type of telescope.  The ones I
> saw had 3 elements but the book says that you can get by with 2 on some
> designs.  Again, the ones illustrated where almost flat on one side and
very
> slightly concave on the other.
>
> David
>
>
> In a message dated 9/18/2002 3:58:12 AM Pacific Daylight Time,
> de_ugarte@terra.es writes:
>
> << I've seen a design of a Ritchey Chretien which uses an
>  Offner compensator at the Cassigrain focus which is made
>  from two crown elements.
>  Could someone explain to me what is the purpose of
>  these additional optical element?
>  Thank you very much,
>
>      Antonio >>