Last updated: 26 April 2005
Subject: ETX125 focuser shift Sent: Sunday, April 24, 2005 05:40:10 From: P. Clay Sherrod (email@example.com) Hello Alan... Focus shift can be caused by MANY issue, but typically is just one...you need to remove the OTA from the rear cell; unscrew the focuser shaft about half way (CCW) and remove the knob or electric focuser unit; there are three very small hex cap screws which hold the OTA into the rear cell; remove these and save in a tuna can or similar, because they WILL get lost if you place on the countertop. Once done, merely grasp the blue OTA in one hand with a rubber glove for grip and the rear cell/fork arms in the other hand and pull gently apart....do NOT twist while separating! You will see where the threaded focus rod inserts into the OTA....typically binding is causing the shifting, but most of this is due to poor milling by Meade on some 125 models. You can improve these imperfect models greatly, but do not expect to eliminate all focus shift. Run the focus rod gently all the way CCW until you feel pressure...do NOT force or you will damage. Once there apply a thick grease, such as pure white Lithium (available in the tool dept. at Lowes) in a very thin layer, pushing hard into the threads...do NOT apply too much or you risk getting this stuff on the optics eventually. Once done, put the knob on the rod temporarily and run it in and out all the way slowly about 3-4 times. Once done, run it HALF-WAY between all the way and all the way out and stop. At that position, turn the OTA to about a 45-degree tilt, with corrector down and put 1-2 DROPS of 3-in-1 oil right where the threaded rod goes into the threaded rear cell of the scope and QUICKLY run the focuser CLOCKWISE to get that thin bit of oil into the rear cell threads. Once done, run the threaded rod slowly all the way CW and then CCW about 2 more times. This procedure will greatly improve the performance....NOTE: do NOT put more than 2 drops of oil on the rod! Take your time and do this very methodically....if you get in a hurry you will be worse off than you started and can greatly mess up the works. This procedure will NOT affect collimation or GO TO operation at all with the scope. Good luck! Dr. Clay -------------------- Arkansas Sky Observatories Harvard MPC H41 (Petit Jean Mountain) Harvard MPC H45 (Petit Jean Mountain South) Harvard MPC H43 (Conway) Harvard MPC H44 (Cascade Mountain) http://www.arksky.org/ ----- Original Message ----- From: Merv Hello, please forgive me for mailing you out of the blue but I have tried to find info & solutions to my problem without success. Can you give me any info on the focusing mechanism & what if any things I can do to stop or improve the awful image shifting when focusing, the image shifts more than half way across the FOV when using, as an example, the 26mm eyepiece & when using a DSI or PSI of course it shifts completely out of the FOV before getting to the focus point, the image then shifts the other way when reversing the focuser. It makes using the DSI or LPI almost unusable. If I take the rear end apart will I need to re-collimate ? Thanks for any help or info Alan
Return to the top of this page.
Go back to the Tech Tips page.
Go back to the ETX Home Page.