Quote:
Originally Posted by Satchmo
Here's the translation of optical tests on two GSO 8" RC .
Scroll down for interferogram and star tests, ronchi and phase contrast photos ( to see surface roughness ) on two different instruments .
Strehl ratio of 0.56 and scary level of surface roughness on these instruments proves the old adage " you get what you pay for". Compare the smoothness of the ronchi bands ,phase contrast test and star test , with the refractors on this page. How much this effects prime focus photography I can't say but it is not desirable.
http://tiny.cc/XSmyf
Mark |
Mark,
For such a low strehl ratio I'm assuming they did not take into consideration the large CO. I have no idea of how large the CO is on this scope, but hypothetically if it were say 35%, then the maximum strehl you can get is 65%, so 56/65 = 86 strehl, which would put the two mirrors as diffraction limited. Apart from that I have to agree that the star test in the lab looks terrible, and the optics appear to have pretty rough surfaces.