megrez focus lock slipping?

[Astroblagger]

Hello was out trying to image m51 last night, i would slew to a bright star focus with live view and then slew back to m51 after the first couple of exposures it was obvious that the camera was slipping back in the focusser, the focus lockscrew was as tight as i could get it, i could push the tube in and out with my fingers when it was locked, does the tension adjust screw effect the lock of the focusser? Im hoping thats all that needs tightened? Anyone else have any similar problems?

[brantuk]

Under the focuser and next to the lock screw are 4 screws arranged in a square and dead centre of which is a tiny hole with an allen key headed screw recessed inside. That will adjust the friction of the focuser when you turn it clockwise.

Don't tighten it too much - needs to be just enough to give good friction on both course and fine focusser knobs whilst at the same time allowing controlled movement. Do it with the camera attached and the scope elevated to find the right point at which it no longer slips. It's a fine balance between that and the lock screw

[brianb]

If the tube is slipping, the focus lock bolt won't help. Get instructions & adjust the focuser so it doesn't slip so badly. I say "get instructions" because doing the job incorrectly can permanently distort the focuser tube, making it impossible to work smoothly without slipping over the whole range of travel.

Why don't the Chinese use a rubber-coated friction roller as per the original Crayford design? Smooth metal on metal is just asking for slippage even if the action is smooth & light.

[brantuk]

I allways wondered that myself Brian - metal on metal just seems daft I agree

[Astroblagger]

thanks for the advice brian, iv adjusted it in half a turn put the camera and flattener in and held the scope pointing vertical and fired off repeated shutter shots no movement! whole night of imaging wasted as i didnt have an allen key out last night, very frustrating!

[ollypenrice]

This, and overly short main tubes, are often to found on WO scopes. My 66 is another offener on both counts. Silly design in what are otherwise rather nice instruments.

Olly

[NickK]

One extreme option would be to glass paper the roller and only the thin path the roller takes down the focuser tube. Would kill the resell value and invalidate the warrantee but I did say it was extreme