View Full Version : New scope - Celestron 8" SCT, HELP!!

2002-Dec-25, 10:17 PM

I just received an 8" Schmidt Cassegrain telescope with all the bells and whistles. However, I do not know whether I need to realign the main mirror. I live in Florida where the seeing is considered 'good' (all stars are visible in the little dipper). When I compare side-by-side visual observations of Jupiter with my 60mm refractor and my 8" SCT, it almost looks like I can resolve more using my 60mm refractor. On the 8", I can only resolve the disk, 2 main belts, and the four moons. I cannot even resolve the large moon of saturn. When I use my 9mm eyepiece, all objects become badly distorted and blurred. What do I need to do? Will a main mirror realignment solve this issue? Thanks!


2002-Dec-26, 05:45 AM
You may need to collimate the telescope. That usually involves adjusting the three screws on the front of the secondary mirror at the front of the corrector plate.

Here's the test. Find a nice fairly bright star near the zenith. Focus on it. Now, unfocus the telescope so you can see diffraction rings. You might try this with the 9mm eyepiece as it is easier to see at higher magnification. The diffraction rings should be perfectly conecnetric circles. If they are not, you probably need to collimate the telescope.

It's easier to do this with two people for an 8" SCT. One person should look through the eyepiece while the other SLOWLY adjusts the screws until you get perfectly concentric circles for the diffration rings. Be VERY careful adjusting the scews...you don't want to accidentally turn them too far and have your secondary mirror fall off! This would risk scratching the primary mirror, secondary mirror, or both and then you would have to remove the corrector plate to fix it...which is always an adventure (trust me on this one...you don't want to remove the corrector!)

Here is a page on collimation...


Hope this helps.


2002-Dec-27, 02:29 AM
Thank you for the info! I look forward to trying this!