Re: [ATM] 7 inch sphereical mirror

[Alexis Cousein <al@sgi.com>]

Dominic-Luc Webb wrote:
> Did I miss something? My understanding was that coma is the
> price paid when you make a parabola. Spherical aberration is
> what you get with a sphere. 

You also get coma and astigmatism off-axis with a sphere - though
the spherical aberration usually dominates the coma until you
get quite far off-axis, it's there.

Coma of the concave mirror (for a given aperture and focal length)
for infinity objects is independent of its conic for stops at
the mirror.

It does change with the aperture stop position, and the way in which
it does depends on the conic constant (you can't change it for a
paraboloid, but you can cancel coma for a sphere with a suitably
chosen aperture stop).


-- 
Alexis Cousein                                  al@sgi.com
Senior Systems Engineer/Solutions Architect     SGI/Silicon Graphics
--
<If I have seen further, it is by standing on reference manuals>
_______________________________________________
ATM mailing list http://www.atmlist.net/