[ATM] Conic Constant

[bmarriott at pacbell.net (Bill Marriott)]

Hello folks;

Well, it has been noted that as a mirror equalizes in temperature with 
the surrounding climate, and which is typically of lower temperature 
than the mirror, ones sees a bit of  OVER correction in the glass, as it 
stabilizes, just as when testing a mirror, when you come back the next 
day and test again, usually the mirror has settled out less corrected 
than when you looked at it the night before.

So, I guess in theory one could leave the glass slightly undercorrected, 
as one may find them selves in a constantly changing downward 
temperature situation.

However, when those perfect nights of spectacular seeing arrive, I think 
I would rather have a accurately figured parabola and the proper 
equipment to keep the mirror equalized with the outside temperature.

Bill Marriott
Woodacre, Ca.



Ray@J-Engineering.com wrote:
Hi All,

I'm not sure where I read it, but it was suggested that the pros will 
often leave a mirror slightly under corrected when figuring. Can this be 
described in terms of a "Conic Constant" say perhaps K=-.95 when using 
Figure XP?  Or is it simply leaving edge up a bit?

Is this adjustment to perfection a good idea? Comments?

Ray

Ray@J-Engineering.com wrote:

> Hi All,
>
> I'm not sure where I read it, but it was suggested that the pros will 
> often leave a mirror slightly under corrected when figuring. Can this 
> be described in terms of a "Conic Constant" say perhaps K=-.95 when 
> using Figure XP?  Or is it simply leaving edge up a bit?
>
> Is this adjustment to perfection a good idea? Comments?
>
> Ray
>
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