The collimation of this telescope is difficult mostly because the secondary mirror cells don't have position gauges (allowing control of what you are doing) and the f/13.5 cell is not kinematic at all but rather a complex puzzle where center and tilt are sometimes coupled on a single screw... So follow this guideline to avoid a nightmare. For your reference, the best images (FWHM) obtained for typical R-band 30sec exposures are: 0.60" at F/13.5 on-axis (classical Cassegrain) and 0.85" at F/7.5 over the FOV. (RC Cassegrain)


F/7.5 : start with this focus, it is easier!


F/13.5: the tough one!!


IN PRACTICE, start with F/13.5. Tweak the tilt of M1 to get proper collimation at F/13.5. Then flip to F/7.5 and if the collimation is not adequate, use ONLY the adjustment screws (center and tilt) of M2 to get it right. DO NOT modify the tilt of M1 anymore obviously. The reason of that strategy is that you can't re-tweak the F/13.5 M2 at night-time while you can with the F/7.5 M2. I repeat: DO NOT in any case use the adjustment screws of F/13.5 M2 at night time because you will mess up everything.


Notes about gravity effects and mirror flips:


Some useful notes for the Hartmann screen method:



Maxime Boccas, 9sept00, last updated 19june01