Quote:It looks like it's an optimisation problem - not finding a true minima so there are likely to be problems plugging any mirror / lens combination into it.
Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schiefspiegler,60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4" f/12, 4.5" f/16 & 6" f/12 Schupmann Medial refractors, 4" Celestar, 19 Stellafane awards 9 in optics Engineering = Taking what you have and making what you need.
Quote:Just a nit: It's "OSLO", not "OLSO". If you Google "OLSO" trying to find OSLO-EDU you'll just find the "Olson twins"! Mike
Quote:Since this is a fast mirror the focal length is going to be short as well so one could also use oil flat with the telescope point down at the flat. I would use the Ross to get you close as you can then use the oil flat to hone in on the final correction.
Ed Jones ........... The best data is an interferogram, the best analysis is from an honest optician.
Quote:I have 3 coated flats. 6in, 9in and 19in but have no idea how flat they are
Quote:I agree, an oil flat autocollimator is a good alternative but you would need to at least partially silver the mirror to avoid the huge light loss. Silvering isn't that expensive to do however. Hanging a mirror upside down might be tricky but you might stick it to the mirror flotation using 3M 2 sided tape (with edge clips just in case).