Trouble collimating telescope - Tilted Forum Project Discussion Community

Herk · 08-30-2009, 10:03 AM

I recently got very interested in astronomy. I've been interested my whole life, but never had telescopes to realize how interested. I saw Jupiter through the refractor I got my daughter and was immediately hooked. I now have a 1000m f/8.8 114mm reflector. I have enjoyed it very much but noticed some problems that after a lot of reading I came to realize are aberrations caused by misalignment.

I have spent a lot of time trying to correct this. I'm failing. I'm not sure if I lack the proper tools or understanding; possibly both.

Essentially I can get the secondary to be centered in the focuser and line up the primary so that the center of the light from my cap with center drilled hole is dead center in the mirror. Great, except for one thing that none of the instructional articles seem to mention. Even once both of those tasks are accomplished, the fully illuminated field is not fully visible.

It seems there are three variables, but only two that I can sort out how to adjust. When I adjust the secondary or the primary to try and compensate for this problem my center ceases to be centered. Please help me.

p.s. If there is anybody in the greater Kansas City area willing to help, I'd love to get together. I'll be joining the ASKC soon, but I want to get my reflector working soon.

BadNick · 08-30-2009, 05:41 PM

I suspect you've already tried to read up on it? ...since I like Sky & Telescope magazine I went to their site and found this: SkyandTelescope.com - Do It Yourself - How To Collimate Your Newtonian Reflector in case it may be of some help to you. Otherwise, I've never collimated a reflector so I have no direct knowledge.

Kingruv · 08-30-2009, 08:37 PM

There are some possible kinks that are effecting your problem.
1. It is possible, even likely, that your primary does not share both a geometric and optical center. On a parabola this size, it might be harder to determine than on a larger one.

2. Are you near the edge of run out on your adjustments? If so, torque could be effecting the shape enough to push it out of alignment. It may measure right but is the reflection diluted as a coma a little?
Many times adjustments are "iffy" near the terminal ends and don't move correctly as in the middle. Again at this diameter it can be more challenging than with a larger one.

Depending on materials there is also the temperature variable that can skew your setup.

Just some food for thought. Hopefully health food and not junk food.

Herk · 08-30-2009, 09:52 PM

I have read that article. It is a good one. They even have a sidebar on just this subject, but I cannot seem to accomplish the primary mirror this that they speak of without moving off center.

The parabolic mirror having two different centers seems possible. Thanks for the help.

08-30-2009, 10:03 AM	#1 (permalink)
Herk Insane Location: Kansas City, MO	Trouble collimating telescope I recently got very interested in astronomy. I've been interested my whole life, but never had telescopes to realize how interested. I saw Jupiter through the refractor I got my daughter and was immediately hooked. I now have a 1000m f/8.8 114mm reflector. I have enjoyed it very much but noticed some problems that after a lot of reading I came to realize are aberrations caused by misalignment. I have spent a lot of time trying to correct this. I'm failing. I'm not sure if I lack the proper tools or understanding; possibly both. Essentially I can get the secondary to be centered in the focuser and line up the primary so that the center of the light from my cap with center drilled hole is dead center in the mirror. Great, except for one thing that none of the instructional articles seem to mention. Even once both of those tasks are accomplished, the fully illuminated field is not fully visible. It seems there are three variables, but only two that I can sort out how to adjust. When I adjust the secondary or the primary to try and compensate for this problem my center ceases to be centered. Please help me. p.s. If there is anybody in the greater Kansas City area willing to help, I'd love to get together. I'll be joining the ASKC soon, but I want to get my reflector working soon. __________________ -Blind faith runs into things!-

08-30-2009, 09:52 PM	#4 (permalink)
Herk Insane Location: Kansas City, MO	I have read that article. It is a good one. They even have a sidebar on just this subject, but I cannot seem to accomplish the primary mirror this that they speak of without moving off center. The parabolic mirror having two different centers seems possible. Thanks for the help. __________________ -Blind faith runs into things!-

08-30-2009, 05:41 PM	#2 (permalink)
BadNick Riding the Ocean Spray Location: S.E. PA in U Sofa	I suspect you've already tried to read up on it? ...since I like Sky & Telescope magazine I went to their site and found this: SkyandTelescope.com - Do It Yourself - How To Collimate Your Newtonian Reflector in case it may be of some help to you. Otherwise, I've never collimated a reflector so I have no direct knowledge.

08-30-2009, 08:37 PM	#3 (permalink)
Kingruv Upright Location: NoVa	There are some possible kinks that are effecting your problem. 1. It is possible, even likely, that your primary does not share both a geometric and optical center. On a parabola this size, it might be harder to determine than on a larger one. 2. Are you near the edge of run out on your adjustments? If so, torque could be effecting the shape enough to push it out of alignment. It may measure right but is the reflection diluted as a coma a little? Many times adjustments are "iffy" near the terminal ends and don't move correctly as in the middle. Again at this diameter it can be more challenging than with a larger one. Depending on materials there is also the temperature variable that can skew your setup. Just some food for thought. Hopefully health food and not junk food.