Re: ATM Star Testing

[Aart Olsen <aart@uiuc.edu>]

How good would a subdiameter almost-collimator be for an artificial star
test?  Many mirror makers have a fine old 6 inch mirror lying around:  a
light source and pinhole slightly inside its focus will cause a beam from
this to spread out to the width of a larger mirror being tested.  This beam
will be closer to parallel than the glint from a ball bearing or other
point source, meaning it might be usable from a few dozen yards away
instead of many dozen.  Anyone up for ray tracing this to see if it is
practical?  If so one could build a permanent almost-collimator, a simple
telescope with a focusable light source near prime focus (no secondary).

At 06:37 AM 2/25/97 +0000, Stephen Tonkin wrote:
>"Robert  C. Pfaff" <PFAFF2@delphi.com> wrote:
>> to test a corrected
>>mirror like a star test you need a collimating lens or mirror  to get
>>parallel light. It should be as large as the mirror being tested.
>
><PEDANTIC>
>Forgive my pickiness, but I think that last sentence would be better as
>"...should be at least as large ..." to avoid it being misinterpreted to
>mean "... exactly as large ..."
></PEDANTIC>



Aart M. Olsen         mailto:aart@uiuc.edu          217-244-4688
Library Systems Office      Univ of Illinois at Urbana-Champaign