This is a 6"F/6 (152/900) Maksutov Newtonian of the lower level quality. It has very smooth optics, strehl will be at least 96 % maybe 97% and show an crisp airydisc with a fainter 1st diffraction ring. The central obstruction looks bigger, because it was tested against the 10"F/5.5 MN with 57 mm secondary. My rating on this MN is about 1/5 wavefront p.t.v. Due the smooth optics it will be very hard to tell any difference against an better sample, if you observe only infocus.
Markus Ludes (APM)