I recently purchased a Nexstar 80GT (80mm f/5 refractor) and was very dissapointed with the views I was getting. I could barely get Jupiter to focus at 50x, it looked like a very fuzzy ball and the 2 brightest cloud bands were not visible at all, stars also looked really fuzzy. I also noticed that I was getting much sharper images using my 45 degree correct image diagonal...wierd. I put a cheshire eyepiece into the star diagonal and immediately discovered the problem (see left circle in the image below to see what I mean). I figured the diagonal was completely screwed up so I took it apart. The mirror was definitely glued in crooked with rubber cement which I removed pretty easily. I put it back together and put the cheshire back in (see the right circle in the image below) what a difference. I went back outside to look at Jupiter and I could see a 200% improvement, disk was sharp and cloud bands were bright. I knew the image could probably be even better if I got everything perfectly centered in the cheshire so I took the diagonal apart again, put 2 small strips of double sided tape on the back of the mirror, stuck it in place, put the diagonal back together and stuck the cheshire in....everything looks perfectly centered now (how is that for luck?). Unfortunately I'm too tired to take it back outside and see if my final tweak made a difference. I can't wait to test it tomorrow and see if I can actually push this scope up to 100x.
I just thought I would share my story in case any one else has a short tube that doesn't seem to be performing very well...give the diagonal a close look and see if it could be the cause of your problems.
I just thought I would share my story in case any one else has a short tube that doesn't seem to be performing very well...give the diagonal a close look and see if it could be the cause of your problems.
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