ATM chipped mirror

["Jan van Gastel" <jhm.van.gastel@mdw.vu.nl>]

Today Steve Swayze emailed me that my 20 inch f/5 mirror is back from the
coater (Spectrum). But: during the coating proces somewhere, a chip came of
the edge. It is about 18 mm wide and 13 mm in from the edge, as Steve says
"like putting a fingernail on the edge". According to Steve this will have
absolutely no visible effect on performance at all. Well, I can calculate
that the drop in limiting magnitude is about .001 magnitude, so that's
nothing of course.
Steve is very sorry that it happened of course and he offers me to make a
new one, or a refund of $300,- when I keep this one.
Another important thing to consider is that this mirror is one of Steve's
top ten mirrors (he also told me that before the mirror went to the coater
and I have no reason to doubt that). These are his exact words:

"It's surface smoothness, and transition of the parabola smoothness are
excellent. It's correction is fantastic too.  It's the way I wish every
mirror could come out. This mirror is probably in my top ten percent of the
best mirrors that come out of here".

For me functionailty is more important then aesthetics and I think I will
keep the mirror, given what Steve says about the quality. But I want to be
absolutely sure that the performance will not suffer, for instance: will
the chip give extra visible diffraction effects?  I  would appreciate every
advise on this subject very much.

Jan
http://www.geocities.com/janvangastel/