Re: [ATM] Re: Aplanatic Gregorian

[Jarvis Krumbein <jkoptic@juno.com>]

Lou, the figures for both primary and secondary are no harder to do than
any other surface using the Focault test.  Remember that you can consider
the primary as a less than fully corrected paraboloid and the secondary
can be null tested.  Null testing the primary is also possible but
probably not too practical.  Look at the numbers that Valdimir has has
supplied and you will see what I mean.

Jarvis Krumbein

> Perhaps aplanatic Gregorian is too difficult.  What about a 
> 'compensating'
> non-aplanat Gregorian?  (I know, that's my term, and it may not be 
> correct,
> but so far other folks have only mentioned the standard Gregorian 
> and the
> aplanatic Gregorian).  I'll try to explain what I'm getting at.  
> First some
> definitions.
> 
> A.  Standard Gregorian:  Paraboloid primary, concave elliptical 
> secondary.
> But not corrected for coma...so it's not an aplanat.  (And this is 
> not, by
> my use of the words...a 'compensating' Gregorian.)
> 
> B.  Aplanatic Gregorian:  (Type of primary?  type of concave 
> secondary?  I
> don't know yet.)  Corrected for coma (and spherical aberration).  
> (If I
> understand it correctly this IS, by my use of the words...a 
> 'compensating'
> Gregorian.)
> 
> In my earlier posts I asked if there were any designs/guidelines out 
> there
> for a 'compensated Gregorian.'  My intent was to have a Gregorian 
> that uses
> two concave mirrors, that are both easy to fabricate and test 
> (hopefully by
> null testing at conjugate foci), that is corrected for spherical 
> aberration,
> but not necessarily for coma.  In other words it's not an aplanat (B 
> above),
> but it's not A either.  That's because by themselves either mirror 
> can't
> form a perfect on-axis image...like type A can with either of its 
> mirrors
> used individually.  (And I presume type B can't form perfect on-axis 
> images
> with a single mirror...but I'm not sure)
> 
> So...a compensating Gregorian is not like type A...but it could be 
> type
> B...although I consider type B an 'over engineered' compensating 
> Gregorian
> because it not only is corrected for spherical aberration, but coma 
> as well.
> (I suppose you could say that the aplanatic Gregorian is a subset of
> compensating Gregorians.)
> 
> Do such compensating Gregorian (non-aplanat) designs exist?  Are 
> they easy
> to fabricate/test...or do you end up with very aspheric mirrors that 
> make it
> too much trouble, etc.?
> 
> Thanks in advance.
> 
> Tom Krajci
> Albuquerque, New Mexico
> 
> PS.  If I'm using bad terms/definitions...please straighten me out.
> ---
> Outgoing mail is certified Virus Free.
> Checked by AVG anti-virus system (http://www.grisoft.com).
> Version: 6.0.799 / Virus Database: 543 - Release Date: 11/19/2004
> 
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 


________________________________________________________________
Juno Platinum $9.95. Juno SpeedBand $14.95.
Sign up for Juno Today at http://www.juno.com!
Look for special offers at Best Buy stores.
_______________________________________________
ATM mailing list http://www.atmlist.net/