[Satchmo]

Originally Posted by ericwbenson

For a big telescope the artificial star need to be <very> far away (impractically) to be of any use, or you swamp the test image with S.A., so the collimating scope is not the problem, it's the <very> long hallway one needs, see here for example: http://www.telescope-optics.net/two-mirror2.htm#Close_objects_error

Regards,
EB

For a final end star test for commissioning a telescope you just need a collimator telescope which produces a parallel light beam into the aperture of the telescope you are testing . Celestron used one of 22" aperture . In the 80's I made and tested hundreds of mirrors at Astro Optical Supplies by 'looking' into the collimated 14" F6 mirror of good quality which had a laser shining on a ball bearing at the focus of the collimator mirror . Also tested many Celestrons that came in, this way .

If you want to test a scopes off axis image quality , you just tilt the telescope to put the artificial star as far off axis as you want to look at ( and of course you could do all that at the focal plane of CCD if you wished ) . If you need to look at the polychormatic performance of the 'scope you just use a white light source .This is an optical testing technique that goes back to the 18th Century. If a manufacturer wants to rigorously test a compound telescope before delivery , this is the way to do it.

Hope this helps.