[Raytrace] Sagitta in ZEMAX

[Richard F.L.R. Snashall]

For symmetric surfaces, a little trick I discovered
for ZEMAX users:

Add a surface succeeding the given surface, separated
from it by the ball radius of your spherometer.  Set
the semi-diameter equal to the semi-diameter of the
spherometer, and choose the surface to be a solve
of the type "concentric radius" (or "concentric surface",
but all my surfaces are spherical, so I'll leave it
as an exercise for the reader).

In <Analysis><Calculation><Sag Table> for that surface,
the sagitta at the maximum dimension given is equal to
the spherometer reading for that surface, with the
following conventions:

         1) the ball radius is "positive"
         2) it is a second surface... for first surfaces,
            I insert a pick-up surface in between with
            the negation of the original surface, and
            reference that new surface.
         3) Sagitta follows ROC in sign.

I found it useful as a quick "calculator".  An alternative
to using the buttons is to set up values in the merit
function using "SAGY".

	Rick S.