scope not holding focus

[cpsTN]

My scope, M500, is not holding focus. It seems that the stage is slowly falling, not enough to see, but enough to notice that the focus moves while observing. There is a hole on the side of the focus knob shaft that I assume the wrench fits to tighten the focus. I no longer have this wrench. Am I correct in this and if so, without the wrench, what do I do?

[Charles]

You can try using a couple of small nails which will fit the holes in the knob as snug as possible , one on each side and turn.

[lorez]

On one side of the coarse focus shaft there is a torque adjustment nut. There are three small holes to receive the C-wrench you are missing. Turning the nut toward the arm will increase the torque and stop the slippage. You may be able to tighten the nut with your fingers or you may have to use a pair of pliers and some suitable padding to protect the nut.

The spanner pin holes in the round nuts on the coarse focus knobs are not related to your problem.

lorez

[cpsTN]

Brad nail came the rescue. Thank You both.