Collimation C-9.25

My brand new C-9.25 with XLT just arrived Friday. It is quite a beauty on my G-11. Very easy to handle. I am quite thrilled with the fit, finish and ease of set up. But things went downhill from there.

I got home at about 8:30 P.M. and began to inspect everything. I then changed out the Celestron Dovetail with the Losmandy. It was very cloudy, so I went to bed. At 2:30 A.M. it was clear so I set the OTA outside and allowed about an hour of cooldown time. It was about 35F here in Northern KY. At about 3:30 A.M. I turned my attention to Jupiter. Of course I had a double image, but I could see the bands clearly and discern color variation of the four principle moons. I was delighted with the size increase over my refractor. The moon showed great detail at nearly 200X, but not tack sharp. Obviously collimation was the issue.

I bought Bob Knobs before the OTA arrived and decided to install them Saturday morning. I did so according to instructions. I spent a little more than 50 min. with the procedure for collimation as outlined in the provided instructions. I could tell it was a little off in the very center of the mirror reflections. I waited until the late evening and tried the scope again. I really destroyed collimation. I could get no real focus on Jupiter, the moon or any stars. I tried star collimation and got nowhere.

Inside the house on Sunday morning, I spent an hour and a half fighting with collimation. I cannot get the mirror reflections concentric.

I have poured over many website pages, reading the advice of others and two methods keep coming up.

1. Star Collimation.
2. Star diagonal or laser collimation.

Everything I read says that I will get it eventually and that it will be an easy task one day. One excerpt said that is some months . . . it will be easy. Wow!

Any advice?

Thanks,

Steve

Stick with it. Normally collimation with an SCT is quite easy. You are at a point I have been at before. The collimation is so far off that any adjustments you make seeem to have little affect on the appearance of the diffraction pattern. If you are way off. Use the intensity of the diffraction rings to let you know where the secondary is. Obviously you want to be able to see the shadow of the secondary, but if it is way off that may not be possible. So, take note of what part of the diffraction ring is the brightest. Now, as you make a small adjustment, note if the intensity changes. Ideally the intensity will begin to fill the rings equally. As it does this, the shadow of the secondary will become defined.

I hope that is not confusing. It really is easier than it sounds. Say for instance you are defocused on a star. You note that the rings are far from being concentric. Normally you woud make an adjustment and then check again. But if it is way out, then an adjustment may have no visible affect on the placement and concentricity of the rings. The intensity of the light however will be affected. As you get closer to being in collimation, the rings will have an equal amount of energy all around the central shadow. So, make an adjustment. Note if the energy distribution in the rings has changed. If so, is it moving in the right direction? If not, go the other way, again in small steps.

I have been at the point that you are at before. I know from experience it can be frustrating. I find it best to do it with a star. Just take it slow and you will be able to get it close again. Once it is close, just follow normal collimation procedure. After you have it properly collimated it is very easy to maintain.

Good luck.

In addition to what the others have said, get a buddy (unless you have incredibly long and nimble arms). With one guy up front, and another watching the changes, things happen a lot quicker.

And unless it is uncomfortable, leave the diagonal in until you get it colose. That is just for convenience. It can be awkward to see a star without a diagonal, and awkward is really frustrating. Then, when you are close, lose the diagonal.

Alex

I use a converted flashlight for an artificial star to collimate my NS8GPS indoors. My scope require a minimum of 35' for focus, but I use 45'.
The pinpoint of light produces great diffraction rings and it allows me to collimate pretty quickly by this means.
Check this post for pictures of it.
http://www.astromart.com/forums/viewpost.asp?forum_post_id=281174&poll_id=&news_id=&page=