Olympus BHMJ

[Smokedaddy]

I am putting the finishing touches on my mockup horizontal rig and was doing some testing yesterday. I have a couple of questions but I need to figure this out first. It is very difficult to achieve a sharp focus when rotating the fine focus knob on the BHMJ. As soon as I get the specimen in focus and carefully remove my fingers from the knob, it goes out of focus. I am only taking about 4x magnification with a MP-E 66mm lens. If I lightly touch the fine focus knob it goes back into focus. I tried rotating the clutch thinking that would stiffen up the movement but that only seems to work for the course knob? Any suggestions before I start looking for something else?

-JW:

[ChrisR]

Suggestion - a spring to take up the slack in the rack. Surgical silicone rubber tubing is better than elastic bands

[Pitufo]

Damping grease on the focus mechanism may help. The grease itself can be quite expensive though.

[rjlittlefield]

Try ChrisR's spring or surgical tubing.

Microscope focus blocks have a large amount of backlash in the gear train, often hundreds of microns. In their normal vertical configuration, that backlash is constantly taken out by the force of gravity as the rack presses down against the gears. In horizontal configuration, gravity doesn't do this job so you need something springy to take its place. Damping grease applied in unusual places could keep the carriage from moving when you don't want it to, but then you'd be left with an annoying amount of backlash whenever you tried to change direction of focus movement.

--Rik

[Pau]

Maybe you have a frequent issue of Oly focus systems if previously someone has done a forbidden mishandling: turning both fine focus knobs in opposite directions unscrews them and they lose its simple holding system: pressure against a wavy washer.

Test if the fine focus knobs can easily rotate in opposite senses (don't force them!). If so, remove the covers of both fine focus knobs and fasten the bolts one against the other with the adequate tool (screwdriver or hex key). If after this operation it still has not enough resistance to hold its position, dismount the knob that holds the wavy washer (usually sandwiched between two plastic washers), the opposite to the one supporting the axis, and curve it if it has lost its original curvature.
I've done these operations many times as at the school lab we have Oly CH clone microscopes and teens are so rude...

[Smokedaddy]

Thanks for all the suggestions. It's appreciated. I ended up using something else.

-JW: