C9.25 mirror locking

Goo points Dave. I think I'll have to pop the OTA open and see whats behind the mirror and measure how much the mirror does travel before making any decisions.

I was chatting to a couple of people yesterday about this again and after describing my problems it seemed that a moving mirror would explain it, but as Carl said, a C9.25 shouldn't suffer from that problem to the degree that I was seeing.

So today I decided to strip things down and have a look at the mirror and see if anything looked wrong.

First thing to do was to take the the autoguider rail and couterweight rail off. Once that was done I noticed that there was a little bit of play between the OTA and the fork. I'd noticed this before but put it down to the mount design and that pushing against the corrector plate probably wasn't a fair thing to do! However today I noticed that the tube (and hence the corrector plate) were able to move independent of the rear cell by several mm. Here's a video to show what I mean:




Time to take things apart.

Getting the OTA off a CPC fork isn't too difficult. Only 4 screws hold the OTA in place, two on each fork. However you need to take the panel off one fork and then loosen the bolts that secure the fork arm to the base (these are really tight - 'I think I'm going to break my Allen key trying to turn this with a pliers' kind of tight) to get enough slack to get the OTA off once you have the four supporting bolts off.

I thought I could then just unscrew the screws holding the rear cell onto the tube. Oh no. For a start, the four screws are held in with nuts so there would be no way to put it back together. Secondly, there were all loose. All of them.

The scope is second hand and I bought it from someone here. The previous owner hadn't done any modifications or cleaning so I can only assume the scope was like this when he bought it. Though perhaps it has loosened a little over time. The support it got from the metal bars for the guidescope and counterweight masked how obvious the problem really was.

So how to get at these screws. The corrector 'cell' is held in by three screws and nuts so you can't take those off either. What you need to do is remove the corrector plate, by taking the six screws on the front out. Then you can reach down with a pliers and tighten the screws. Here's a pic of three of them.



I decided not to mess with the mirror after that. I'll see how much better things are now before taking a drill to the rear cell

Here's a video of the lack of movement now: