[ATM] other Schmidt equations

[Richard F.L.R. Snashall]

Vladimir Galogaza wrote:
> Dominic, Richard,
>
>>   4)  86.6% vs 70.7% neutral zone
>
>
> Rutten & Van Venrooij  (Chapter 21.11)
> "Often the makers of Schmidt correctors wishes to minimize
>  the volume of glass that must be removed. This is achieved  
> when the edge thickness of the corrector is the same as
> the center thickness. For this case.........the position of the 
> neutral zone follows"
>
>                                   NZ=sqrt(2*(Dc/2)^2 /Dc^2) = 0.707
>
> So this is the meaning of 0.707 versus 0.866 choice. 
>
In the same area, it mentions the desire to use the 86.6% zone
to minimize color error.  However, there is reason to believe
that this does not minimize RMS wavefront error; and that it
will be minimized by using the 70.7% neutral zone -- as much
contrary to intuition as that may sound.