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Problem And Solution

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Posted by Bob Sal on June 26, 2001 13:32:50 UTC

Hi Mark;
I have a 12" LX200 with the same problems. The problem is in the design of the SCT telescope. The focusing problems are cause because you are moving the primary mirror to focus. There's a lot of mechanics in there that settle down when you stop focusing. This extra movement when you let go of the focus knob is usually in one direction. For the 12Ē itís when you move the mirror up. I called Meade, they sent me a new focus knob, that really didn't help. What I do is focus in the direction I know it will continue by itself, let it settle down, then go very slowly the other way. It will usually stay pretty good. If you pass the focus, start over again. Yes, some of the problem also stems from the lubrication being uneven. Thereís a procedure to fix that. You disconnect the focus knob from the telescope by removing the 3 screws. Donít take the knob off. Just pull it back and forth about 10 times. This slides the primary mirror up and down the shaft to even out the lubrication. Thereís a big write up on this at Thereís also lots more info there on the Meade telescopes.
Now all this helps, but I have a way better solution. I couldnít take it anymore. I was spending more time focusing (a $4000 telescope)than observing. And if you had more than one person observing, well it was just ridiculous how much focusing was going on. Meade should really try to fix this problem. I see it on almost all SCTís Iíve seen. Image shift, unfocusing all by itself, backlash, but it seems worse on the Meadeís. Anyway, my final solution was this. I bought the JMI NGF Manual Focuser for SCTís. This is a rack and pinion focuser that attaches to the back of the telescope. Very easy to install. You then use the regular focus knob as a rough focus only. Get it as good as you can, then use the JMI for the rest of the night. Thereís enough play so most people donít need to readjust the rough focus. Sometimes you need to adjust the rough focus when you change eyepieces. After that you focus in seconds just like a refractor. Itís a real pleasure. After I got mine, 3 friends have already gotten theirs. Believe me, itís a huge difference. This should be a standard feature on all SCTís. But of course, in solving one problem I created another. With the JMI attached, the telescope no longer cleared the bottom of the fork mount. I couldnít point it at the zenith. Also I had to keep watch when it got close to make sure it didnít hit. That became a pain in the neck. You could use a 1 1/4" diagonal, that solves the problem, but then what do I do with the $1,100 worth of 2Ē eyepieces I bought. Well, I solved that also. The SCT diagonal screws on to an adapter on the back of the JMI. I bought a Teleview refractor type diagonal that slides in instead. Perfect! With the JMI fully extended, I now have a very generous 1/8 of an inch clearance. Good enough. So after 3 months research, $160 for the JMI and $200 for the Teleview diagonal, I solved the focus problem. JMI also sells a Moto-focus which is larger than the manual. Donít know if it will clear the bottom with the Teleview diagonal. I know a guy with it, heís one of the guys who then bought the manual anyway. Itís disturbing than I had to spend $360 + S&H for JMI and Teleview equipment to get my Meade telescope to work properly. What can you do, it works great now and Iím very happy. Hope that helps. Clear Skies and Focusing.
Thatís it;

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