[ATM] what causes coma?

[Hugues.Laroche at ses-astra.com (Hugues.Laroche@ses-astra.com)]

Hi Mark,

>The explanation at the OMI web site is probably technically correct, but
>I find it somewhat incomplete because, the way it describes coma makes
>it seem that coma could arise from a parabolic or spherical mirror.

Hm, good observation. I think the key word is entrance pupil.

If the mirror is the entrance pupil like in a Newt, then
the explanation applies to paraboloid and spherical surfaces
which should both exhibit coma.

Now in Schmidt (with corrector) or a "lensless" Schmidt
(with a kind of iris placed at the COC of the spherical mirror),
the entrance pupil is the corrector plate or the iris. And
then the spherical surface has no definite optical axis anymore,
and each bundle of light focuses w/o coma.

Can an optical guru ;-) confirm? Jim Burrows, Bratislav, others?

Happy optics!

Hugues





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