From: "MARY WINSTON" 
To: mommoteandcoyote{at}msn.com
Cc: atm{at}shore.net
Reply-To: "MARY WINSTON" 


"OH Shirt"!, I forgot to sign my last post...Darn e-mail blew up
last week and I'm on the wifes page now...

Coyot‚







>From: "MARY WINSTON" 
>Reply-To: "MARY WINSTON" 
>To: rob{at}vrf.com
>CC: atm{at}shore.net
>Subject: Re: ATM Ritchey-Chretien telescopes
>Date: Thu, 27 Feb 2003 10:40:15 -0700
>
>
>
>Guys,
>
>The only way to end up with a flat field Ritchey-Chretien... is, (1) to
>introduce a field flattening lens ahead of the focal plane... or, (2)
>design a system in which the primary and secondary mirrors share the same
>radius of curvature.  This means, however that the secondary will naturally
>be one half the diameter of the primary, or so... I built an 8" and a
>12.5", about 20 years ago, using the equal radius method... both were
>F/5.6.  I used an optical window to support the secondary on the 8", which
>I still have.  Photos showed almost perfect images over a 40' field, and
>acceptable ones out to about 1.5 degrees... they enlarged rapidly beyond
>that though.
>
>
>
>
>
>>From: "Rob" 
>>Reply-To: "Rob" 
>>To: "Richard Schwartz"
,
>>Subject: Re: ATM Ritchey-Chretien telescopes
>>Date: Wed, 26 Feb 2003 17:27:30 -0600
>>
>>
>> > I hope you know that the field is flat only when the curve of the
>>primary
>> > matches the curve of the secondary.
>>
>>If I understand things correctly (which I probably don't lol) that is one
>>of
>>the design criteria for an R-C type scope.. They seem to have very low
>>power
>>secondarys and the radius of curvature is closely matched. Most of the
>>ones
>>I have seen have around 2.7x secondary compared to something like 5x for a
>>cassagrain.. I just thought matching the curvature was part of the R-C
>>design...Maybe not though :)
>>
>> >Everybody makes such a big deal out of R-C optics, the cass builders are
>> >driven to D-K systems because they are scared away.   But I see nothing
>>in
>> >the R-C system that is so difficult.  It is certainly no more difficult
>>than
>> >the parabolic primary and hyperbolic secondary of a conventional
>>cassagrain.
>>
>>This sounds encouraging. The only thing I'm really concerned with at this
>>point is trying to grind the secondary. Maybe I should try to buy the
>>secondary???
>>I've never tryed to grind a cassagrain secondary. Maybe this won't be as
>>difficult as it seems...
>>
>> >However, I do suggest that you keep the project to yourself until it is
>> >done.  If anybody asks, just tell them it is a D-K.   Otherwise, you
>>invite
>> >ridicule and discouragement.   Also, while you are at it, get all your
>>old
>> >ATM books that have discouraging words about R-C... and BURN 'em.
>>
>>I'm a loner for the most part. So theres not really many people around to
>>tell..Except you guys :)
>>I think maybe I'll just burn the pages that have discouraging info on R-C
>>scopes.. The rest of the books seem to have useful info I don't want to
>>lose
>>hehe :)
>>
>>Again thanks for the info. you guys have been a huge help :)
>>
>>Rob
>
>
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