Removing the Meade LX200R corrector plate

Submitted by jimwcoleman

There may come a time when you have to remove the front corrector plate from your Meade SCT. In my case, it came when a collimation screw came loose while I was collimating the scope in my sleep on a long, dark night. I guess I wasn't paying attention to how far I had backed out the Bob's Knob when, to my dismay, the knob came off in my hand and I heard the secondary housing partially detach from the corrector plate. Luckily, the other two collimation screws held - or the secondary would likely have fallen down onto my primary mirror and that would have been a catastrophic, expensive mistake.

Here's what you do if something like that should ever happen to you.

First, don't panic. Forget parking your scope and forego your carefully precisioned alignment - you are done for the night. Carefully slew (or unlock and manually move) the OTA so that the nose of the scope is slightly lower than the rear cell. That way, should anything fall, it won't fall down further into the scope.

In the morning, take a deep breath and relax. You are going to remove the corrector and make a repair.

Photo of Dirty Corrector1) In this photo, you can see the front end of the telescope before any disassembly has begun. It's also obvious that the front corrector plate is a bit dirty - I think much of that can be blown off but I'll make an evaluation once the plate is removed. If it requires cleaning, it would be a good time to do that, too.

Photo of Dirty Corrector2) Begin by removing the small hex screws on the ring surrounding the corrector plate, taking great care not to drop them down onto the plate itself. These are not the screws around the front exterior of the OTA - these are the screws you see around the edges of the imprinted retaining ring as you look directly into the OTA. When those screws are removed, set them aside and remove the retaining ring. It would be smart to hold the corrector plate in place with your thumb so that it doesn't fall forward and out of the scope.

Photo of Dirty Corrector3) It is crucial that the corrector plate go back into the scope in the EXACT same configuration it was in prior to removal. To help with that, most scopes have a factory mark that will help with alignment. You can see that mark in this photo. If your scope does not have such a mark, be sure to mark it yourself. The importance of this can not be understated.

See those cork shims around the edge of the corrector plate? It's critical that those shims remain in place, too - or are returned to their original configuration. In my case, none of them fell out - but be sure to carefully mark where they are in case yours shift or become detached. I used Scotch tape to mark their locations. (Note: In general, they will align with the screw holes around the rim. But not always.)

Photo of Dirty Corrector4) After everything is marked and ready, carefully tip the corrector plate out and remove it from the scope. Here you can see the OTA, cardboard shims still in place, but open with no corrector plate. Be sure to cover it with something to keep dust and debris from entering the OTA.

 

 

 

 

Photo of Dirty Corrector5) I brought my corrector plate/secondary into the house and worked on a clean workbench. With the corrector out, it was easy to replace the collimation screw. The secondary rides on inner springs, so it was just a matter of gently pressing down on the edge of the secondary until it made contact with the screw that was inserted in the hole on the opposite side. I turned the screw several turns to secure the secondary. With the secondary securely held now by the three original screws, the corrector is ready to be replaced - which is done by reversing the order of the steps shown above.

With a little care and common-sense, this is a job that can go fairly quickly and with great success.

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Submitted by swingin on Thu, 09/22/2016 - 11:51

Great instructions, I need to clean mine, it's a bit cloudy, but don't want to mess anything up, collimation is spot on still from the factory. I also have Bob's Knobs but I don't even want to install them until it's necessary. Nice work!


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