Mak focuser problems

[james_screech]

I recently bought a second hand BRESSER Messier MC-100/1400 OTA. When the focuser is adjusted stars move significantly in the field of view, perhaps 0.5 degree per turn of the focuser knob. I assume there is a problem with the focuser not moving the mirror linearly in the tube but tilting it as it moves. This is born out as at times stars become comet shaped, implying that collimation is changing with focus setting.

Is it possible to dismantle the OTA and improve the way the mirror moves (re-grease)? I've searched online but cannot find anything myself. Any suggestions would be appreciated. I've found instructions for collimating the scope but that's no good as changing the focus will require it being re-collimated again.

James

[Robindonne]

Its shifting.  Dont know about bresser maks but i’ve read that turning the knob all the way to one end, not sure which, helps setting the mirror and could improve the stability and help with this problem.

Edited March 1, 2021 by Robindonne

[johninderby]

Ypu might want to remove the rear dust cover and check that the focuser shaft bushing is seated into the backplate of the scope. Just remove the focuser knob and the three exposed screws that hold the dust cover on. The collimation screws are hidden under the three black rubber plugs and not the ones to touch.

Here’s what it will look like with the dust cover removed. This is a Bresser 127 mak but the 100 is similar. Notice the shaft bushing isn’t seated.

Edited March 1, 2021 by johninderby