Image of the day

Captured by
Forrest Egan

Green Heron

My Account

New to Astromart?

Register an account...

Need Help?

Re: Collimating a SCT

Started by EdZ, 03/05/2003 09:47AM
Posted 03/05/2003 09:47AM Opening Post

I have a G5, same tube as the C5. The secondary should be secure within the corrector plate so don't try moving that.

Before you try loosening the retainer ring, take measurments as indicated below. If all measurements are equal then there may be something else going on. If measurements are not equal, go on.

Set your mount so the scope corrector plate is face up and lock the mount steady. With the corrector plate locking ring slightly loosened you will be able to gently grasp the back of the secondary and move the corrector plate around. You will need a good pair of draftsman's dividers or a compass or a micrometer. Careful of the corrector lens! Take a reading at all three screws, between the back of the secondary and the inside of the retainer ring, approx 1.75 inches. Gently move the secondary to slide the corrector plate around until the reading is exactly the same at all three points. try not to twist the orientation of the secondary.

This should fix your problem if it is the secondary that is off center. A few years ago celestron was putting out the C5/G5 tube with a lot of complaints about the corrector being loose. I had one. This is one way to fix that problem.