From: "Richard F.L.R. Snashall" 
To:  atm{at}shore.net
Reply-To: "Richard F.L.R. Snashall" 




Richard F.L.R. Snashall wrote:
>
>
>
> Mel Bartels wrote:
>
>> I was asked in a private email the derivation of the deformed shape
>> where:
>>
>> 1. glass considered thin meniscus of constant thickness (ex. 12 inch
>> diameter, 1/4 inch thick)
>>
>> 2. glass supported at extreme edge (supported inward better???)
>>
>> 3. glass facing upward towards zenith
>>
>> What is the resulting shape?
>>
>
> Boy... that sounds like a familiar question (but drop the mirror
> part);-)
>
>     Rick S.
>

It was my assumption that the result would be quite similar to that that
would result from the vacuum deformation that is sometimes used to create a
Schmidt corrector.  However, I have not seen the gravitational force
modelled in that, even though the tool force is.  I do not know if the
result from the vacuum method and that from the fluid method that was shown
in S&T (many years ago) result in different surface functions.

In these cases, the re-grinding of the surface back to a sphere results in
a fourth order (or higher) concavity put onto the surface.  Added to the
concave side of a meniscus, this would result in an oblate surface. 
Presumably, what was removed would have had a prolate (??) surface.

        Rick S.

>> Years ago Tom Lum and I derived this - and I cannot remember for
>> certainty
>> if the shape is parabolic or spherical.
>>
>> Can anyone take a stab or point to articles?
>>
>> TIA Mel Bartels
>>
>>
>>
>>
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