Hi everyone, i'm not quite sure how to describe this problem
i have a BX50 which is generally great. I relubricated the fine focus shaft because it was very stiff and now its great. The only issue is that the fine focus seems to overrun. ie. when you turn it in one direction, it seems to continue focusing very slightly for a little moment after you have stopped turning the knob. Is anyone familiar with this issue and how to sort it out?
Many thanks!
bx50 focus "overrunning"
Re: bx50 focus "overrunning"
I'd guess it's when you're moving the stage away from the objective?
If so, there's likely a tiny bit of slack in the gearing (normal to a bit of wear) and enough viscous damping elsewhere (heavy grease on the cylindrical bearings guiding the downward motion of the stage, for example) that it takes a while for the downward motion to catch up. Gravity soon enough drops it a bit more, to the extent there's any backlash in the gearing (you need and want some clearance). If it's annoying, you might want to do a complete clean and relube so there's less stiction?
If so, there's likely a tiny bit of slack in the gearing (normal to a bit of wear) and enough viscous damping elsewhere (heavy grease on the cylindrical bearings guiding the downward motion of the stage, for example) that it takes a while for the downward motion to catch up. Gravity soon enough drops it a bit more, to the extent there's any backlash in the gearing (you need and want some clearance). If it's annoying, you might want to do a complete clean and relube so there's less stiction?
Re: bx50 focus "overrunning"
thanks PeteM,
I don't particularly fancy taking the entire gearing apart, I'll have to do some reading to see whats involved!! Might not be worth the effort for a minor annoyance (its only really noticeable when using 40x).
Thanks again!
I don't particularly fancy taking the entire gearing apart, I'll have to do some reading to see whats involved!! Might not be worth the effort for a minor annoyance (its only really noticeable when using 40x).
Thanks again!
Re: bx50 focus "overrunning"
I suspect the problem is mostly in the vertical rails guiding the stage. Assuming a BX50 is much the same as a BX40, these will have a series of crossed cylindrical bearings running on vertical rails and with a gib screw adjustment that can be tightened or loosened as needed. Also very similar to the earlier BHS scope, so Carl Hunsinger may have a guide with some helpful hints (check the Alan Wood site for Carl's guides).
Main point being that while it's still a bit of a pain to lube these, you wouldn't have to mess with the actual coarse and fine focus gearing -- and it might solve the problem. You'd want to take pictures on the way in to remember how the bearings are crossed, clean off all the old grease, add new, and then put it back together.
Could also try adding just a couple drops of light oil to loosen the grease. Or, as you say, just live with it until and if the grease further thickens. You have a wonderful scope. A bit of old grease doesn't much diminish that, but eventually you'll want to have it serviced.
Main point being that while it's still a bit of a pain to lube these, you wouldn't have to mess with the actual coarse and fine focus gearing -- and it might solve the problem. You'd want to take pictures on the way in to remember how the bearings are crossed, clean off all the old grease, add new, and then put it back together.
Could also try adding just a couple drops of light oil to loosen the grease. Or, as you say, just live with it until and if the grease further thickens. You have a wonderful scope. A bit of old grease doesn't much diminish that, but eventually you'll want to have it serviced.