ATM Wavefront arithmetic

[Bratislav Curcic <epabcc@epa.ericsson.se>]

Jeff Baldwin wrote

> If you have a 1/10 wv primary p-v  with a 1/10wv p-v secondary then you
> will have a 1/5 wv system.  If you can caustic test your mirror to 1/20 wv
> p-v then you will end up with a 3/20 wv p-v system

The wavefront errors are not apples, and they do NOT simply add.  How
about my Wright camera where I have an 'error' of 12 waves on the
corrector and about 6 waves on the the primary, yet resulting telescope
is not just stigmatic, but aplanatic as well :-)

Bratislav