Removing the drawing attachment from Olympus BH2

[Bruce Taylor]

At the museum lab where I sometimes look at ciliates there are two Olympus BH2 microscopes. One of them has a drawing attachment. The BH2 with the drawing attachment seems to be a bit less brightly illuminated than the other one, and consequently the images I make with it seem to be less clear. Is it possible that the tube is "stealing" light from the path? I am not very smart about optics, so it is certainly quite possible that this is a result of "user error."

To test this, I tried to remove the drawing tube, since nobody there is using it. However, I ran into a small problem. When I loosen the attachment screw (the red arrow in the photo, below) the device becomes loose. However, I can't seem to remove it entirely (the dovetail still seems to be bumping into something). At a certain point, the retaining screw seems to stop turning, and I begin to see threads in the shaft, at the base of the knurled knob (I seem to be removing the knob from the shaft). What am I missing?

Drawing attachment Olympus BH2.jpg (97.71 KiB) Viewed 2312 times

[PeteM]

Hi Bruce - as you have surmised, the half mirror in the dovetail IS taking some light.

For removal, I'd suggest removing the head just to make things easier, back out the drawing attachment screw as you have, and try moving it somewhat forcefully toward the screw and lifting up with a wiggle and maybe a rotation or two.

The screw normally has a little clip on the end that prevents it from being unscrewed all the way. It also may have a spring-loaded plunger in it. If working properly and without the spring-loaded plunger gummed up, once you back out that screw until it stops, the attachment should be removable. If not, the screw or dovetail could be buggered up - or if yours has the spring-loaded plunger (they'll be a screw at the end of the knurled knob) it could have stuck oil. That's why you want to try moving the head back against it. Rotating the drawing attachment a bit once loose might help if the dovetail has been damaged.

Good luck. With all the help you've given us in identifying things, we probably owe you a microscope.

[Bruce Taylor]

Thanks, PeteM. Next time I'm at the lab I'll give that a try. It seems quite possible that the screw oil is gunked up. That was certainly the case with the translation control knob on the prism slider, which required a LOT of persuasion, at first. I think this BH2 has received less love and attention than its twin. I'd like to get it going, if I can, because the slightly-nicer microscope is at the busy end of the invertebrates lab, overrun with big molluscs and other horrors.

[Scarodactyl]

The 1.25x each from it and the polarizer(?) isn't helping either--even with the half mirror not engaged (I assume position 'c' on the drawing attachment has the half mirror out) you've got a ~1.5x empty mag factor and extra lenses not perfectly transmitting light.

[Bruce Taylor]

@Scarodactyl I tried the different settings on the drawing tube (A, B and C) but didn't see much difference in terms of light transmission. There's also a sort of rotating metal "hood" at the distal end of the tube, and when open it throws a distracting shaft of light over the middle of the visual field.

The lower 1.25X is the Nomarski intermediate tube, which carries the DIC prism slider. Gotta leave that one in place.

[deBult]

Bruce,

From memory (not at home so cannot check this weekend) on the more elaborate BH2 stages with removable revolver: the pin for removing the bino unscrews - and then you have to pull it (sliding mechanism INSIDE the pin) practice on that one first by removing the normarski analyzer.

It may well be the nomarski pin has the same mechanism.

PM if you want me to check begin next week.

Best, deBult

[deBult]

There's also a sort of rotating metal "hood" at the distal end of the tube, and when open it throws a distracting shaft of light over the middle of the visual field.

Yep that is exactly what it is supposed to do: the mirror at the end projects the drawing paper and your pencil image on the desk table INTO the Bino (it does not project the specimum image to the paper as some people expect).

[Bruce Taylor]

Thanks deBult! That's all very useful information.

cheers,
Bruce

[Bruce Taylor]

Well, I managed to remove the drawing attachment. It did indeed have a spring-loaded plunger, as PeteM suggested (with a slot-headed screw in the end of the knurled knob). Knowing that "stuck oil" was probably the issue, I was a bit more forceful with the assembly, and pushed the dovetail against the pin as I tilted it slightly and...bingo!

Now, I have another issue...some dust or schmutz somewhere in the light path, creating a dark spot on the image at higher magnification. It seems to be below the head, but I don't think it's on the condenser or light well. Moving the condenser down a bit makes it less conspicuous, but I suppose I'll have to take the head off again and try to blow whatever it is away?

If need be, the museum will call in the technician to service the microscope, but I'd like to spare them the expense, if I can.

Anyway, thanks for all the help, everyone!

[PeteM]

Bruce, Glad you got it free. When that plunger is properly lubed, you'll be able to partly unscrew it and then just pull it back.

As you probably know, a centering telescope can help a bit in tracking down where the junk is. Just work your way down from the eyepieces, through the head, 1.25x intermediate lenses, sliding DIC prism, objective, slide, condenser, field lens . . . and try rotating or moving to see which component has the smudge. The objective is one common fault and easily checked (even without a phase or centering telescope) by unscrewing it a bit to see if the dirt moves with it.

[Bruce Taylor]

Thanks for the advice, PeteM! I'll bring a centering telescope on my next visit (and an air-blower bulb).

[Bruce Taylor]

I was back at the museum yesterday, and set out to analyze the source of the dark spot in the light path. I brought a centering telescope, but it wasn't needed in the end because the problem was not subtle.

There's some loose debris inside the Nomarki/DIC intermediate tube, and a big piece is stuck to one of the glass surfaces. I suspect an insect crawled in there and either shed its carapace, or died:

Debris inside intermediate tube.jpg (34.17 KiB) Viewed 1829 times

The debris is definitely inside the tube, and can't be blown or brushed away from the outside. Since an insect seems to have gotten in, the debris must be in an area that isn't hermetically sealed. I was thinking that I might be able to reach it by removing the slider, then blowing out the dust. If this seems like a good plan, is there something I should know before trying to pull out the slider? I don't want to force anything, or damage the equipment. Is it simply a matter of loosening the slider clamping screw and pulling the prism slider out?

[PeteM]

Bruce, The clamping screw runs in a groove in the slider, so it needs to be backed way out. That should allow you to remove the slider. I vaguely recall an earlier Olympus slider that also had a second stop screw; but don't think you'll have that.

Your plan sounds good. I'd try blowing the prism off first, but I suspect some debris will remain. Let that soak for a while in a drop of distilled water and try a gentle wipe with a cotton or foam swab. You'll likely need to follow with lens cleaner. Be gentle in applying pressure. Worst case, IMO, you'll see damage to the coating, but the prism should still work.

[Bruce Taylor]

Thanks again, PeteM. I'll see if I can remove the debris with a bulb blower and/or soft brush, but if it comes to using solvents (even water!), I think I'll let them bring in the technician!

[deBult]

Thanks again, PeteM. I'll see if I can remove the debris with a bulb blower and/or soft brush, but if it comes to using solvents (even water!), I think I'll let them bring in the technician!

Fair: a functioning BH2 with transmitted light DIC will do 4500-5500 on this side of the pond.

[Bruce Taylor]

Well, that worked perfectly. One quick puff with the bulb blower and all was clear.

Thanks for the help, everyone!