i'm using a newtonian and i believe my mechanical collimation is pretty decent now .i tested it using ccdi real time, several runs, good seeing, 4000 stars, 1 min exposures, 1800mm f.l., and these ranged from 4 to 9 arc sec, averaged around 7 or so. the x/y tilt was consistently in the 0.1 to 0.3 range. can i be reasonably sure that a mirror adjustment is what is needed here and not a secondary adjustment or something else in the optical train?
thanks,
dave

Hi Dave,

CCDI measures the overall collimation of the system and can't distinguish between primary and secondary adjustments. If the overall collimation error measured by CCDI is low, then you can be sure that both are properly adjusted.

You will want to adjust the secondary using the traditional methods (cheshire, sight tube, etc.) When done, finish the adjustment by collimating the primary, using CCDI.

Your overall collimation error numbers sound good to me, so I doubt your secondary needs adjusting.

Regards,

-Paul

thanks paul