Re: [ATM] 7 inch spherical mirror

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

Dominic, all:

Schmidt himself said that he used the vacuum system (not immediately; he 
kept it a "secret" for a while); he told Walter Adams he had everything 
worked out to produce the first aplanatic rapid coma free camera, but had 
yet to devise an "elegant" method to produce the corrector (figure it). 
Finally he did and produced the first one; it had a 17" mirror, and a 14" 
corrector plate, and was either an f2.5 or an f/2; he had a very hard time 
selling it. I don't know if he ever sold it. Walter Adams marvelled at the 
images it gave when used as a Newtonian. Gravestones.

And my sources for where entrance and exit pupil are in any optical system 
are (were) formal.

R-101

P.S.- I forget a lot of stuff that I am not interested in; however, I write 
aviation history and technology articles for MagWeb dot com FROM MEMORY 
only; I remember things about my other great love, telescope making; (also, 
I forget a lot of stuff).

The entrance pupil for a Newtonian or Classical Cassegrain reflector is the 
primary mirror. Show me a source that says otherwise. The entrance pupil to 
the eye is that little dark round circle defined by the iris.

The proper location of an entrance pupil for a Schmidt CAMERA is the 
location of the corrector plate, or aperture. For a Schmidt Cassegrain, the 
situation is different; the rule is usually broken here, I believe. Don't 
know about the Wright camera.

R-101


----- Original Message ----- 
From: "Dominic-Luc Webb" <dlwebb@canit.se>
To: "ATM Superheros" <atm@atmlist.net>
Sent: Wednesday, April 16, 2008 5:16 AM
Subject: Re: [ATM] 7 inch spherical mirror


> On Tue, 15 Apr 2008, David Harbour wrote:
>
>> Thanks; just wanted to have at least some hazy idea of what is going on. 
>> The
>> entrance pupil to any system employing a paraboloidal primary (and also a
>> Ritchey Chretien, as well as a Classical Cassegrain, and the ever popular
>> Newtonian, is of course the primary). The entrance pupil to a Schmidt, 
>> is,
>> on the other hand, at the aperture where the corrector lens is, or should 
>> be
>> (lenseless Schmidt).
>
> Sounds right, albeit this is the pupil diameter, not location. I
> might state that the entrance pupil is located where a corrector
> is not needed. I think entrance pupil may be located at at/near
> the focal length for a Newt, but at ROC for a Schmidt. I deduce
> this not from any academic formality, but what I have seen in
> some Oslo files. For my Schmidt designs (lensless or with
> corrector), it is situated at/near ROC. In examining some
> longer F/ratio spherical mirrors, like F/10, I have also
> looked at smaller entrance pupils, because I am used to
> working Schmidt designs. In my case, it has been issue of
> giving my existing lensless Schmidt designs in Oslo a longer
> F/ratio, such as F/10. This was some years ago, but looking at
> the posts from this list, I think this explains why I do not
> see much coma on a spherical lensless design at higher F/ratio,
> and also not so much spherical aberration. It is very easy
> to change the aperture stop as desired.
>
>
>> Does anyone know that Schmidt himself was reputed to have told someone 
>> that
>> an attempt to figure a corrector plate for any faster system then f/2 by 
>> the
>> vacuum method can, and usually will, break the plate?
>
> I have heard this over and over again. I have a couple of
> articles by Schmidt, or by his collegues. I need to check
> these references again to be sure. I remember something
> to the effect that beyond some critical cutoff, a corrector
> can be added. The deduction is that below that cutoff, no
> corrector is needed. I suspect lensless "Schmidt" (i.e.,
> spherical primary with aperture stop at ROC) designs may have
> once been quite common. I need to check the references I have
> to see if Schmidt specified the vacuum technique, but I do
> not think I do. I would be quite happy to see any reference
> actually from Schmidt.
>
> Does anyone know for sure that Schmidt ever used a vacuum
> method?
>
> Dominic
>
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> 


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