[ATM] Conic Constant

[mbartels at bbastrodesigns.com (Mel Bartels)]

> 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.

My experience is that the spherical aberration change due to lack
equilibrium is surprisingly extreme, and to try to account for it by
undercorrecting fails for two reasons:

1. mirror never cools the same way because the starting inside and outside
temps vary too much
2. when it does reach equilibrium, you are left with a bad figure

Mel Bartels