Quote:
Originally Posted by Den
Here is a link to tweaking up of a Celestron 90, it is not complete but has some good images in helping with visual aspect of alignment.
I like how he has marked the secondary mirror! this would be very accurate.
http://www.tamanti.it/Tips/C90MOD.htm |
I centered spotted my secondary as well. I reckon it's a must. Otherwise you never know if it's centered in respect to the back focus. Very hard to check by looking at the concentric reflection alone. I could never do it.
I also used a board in the past with the pin hole and laser to check the halfway point for the primary focal point but since found that if you get a laser point source and stick some mate adhesive tape on it you can diffuse the light and illuminate the whole primary.
By looking at the secondary shadow in the reflected image you can pretty much get everything bang on. The latest Hotech tutorial explains how to do this on their website.
Problem with sticking a laser at the back of the scope is that you assume it's aligned mechanicaly. If you shine a diffuse laser in the front aperure and look at the secondary shadow and the reflection of the primary you don't care about anything else but the primary. You take the tube out of the equation. So it's always right to start with.