Collimation of Oly BH2 microscope

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Harold
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Collimation of Oly BH2 microscope

#1 Post by Harold » Sat Nov 27, 2021 9:17 pm

I recently watched Carl Hunsinger's video having to do with collimating the light outlet with the microscope's objectives. https://www.youtube.com/watch?v=Y5PvIOe ... lHunsinger A couple questions came to mind. First, it seems to me that collimating to a removable target has some shortcomings. Specifically, what assurance is there that the light input assembly will go back into the base in the exact same position as the tube containing the target, especially since the target tube goes in backwards? And this leads to my second question; just how critical is this collimation? From my telescope days, I understand how off axis light can degrade optical performance, but microscope optics seem to be designed to eliminate it. Just curious...

deBult
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Re: Collimation of Oly BH2 microscope

#2 Post by deBult » Sun Nov 28, 2021 4:57 am

The “removable part” from the light trail has two centering screws and fits a narrow tube: so the position is pretty precise.

@Apochronaut: please give us some guidance on the importance of collimation of the lighting system :?:

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josmann
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Re: Collimation of Oly BH2 microscope

#3 Post by josmann » Sat Dec 04, 2021 7:42 am

Harold wrote:
Sat Nov 27, 2021 9:17 pm
I recently watched Carl Hunsinger's video having to do with collimating the light outlet with the microscope's objectives. https://www.youtube.com/watch?v=Y5PvIOe ... lHunsinger A couple questions came to mind. First, it seems to me that collimating to a removable target has some shortcomings. Specifically, what assurance is there that the light input assembly will go back into the base in the exact same position as the tube containing the target, especially since the target tube goes in backwards? And this leads to my second question; just how critical is this collimation? From my telescope days, I understand how off axis light can degrade optical performance, but microscope optics seem to be designed to eliminate it. Just curious...
Hi Harold,

I think the answer is that it's not critical at all in most cases. I believe the light input assembly would need to be dramatically out of position to be noticeable beyond the field lens. All you're doing with that positioning is changing the maximum angle light that traverses the field iris - I think the only consequence of misplacement would be a loss of peak brightness. The field lens focuses an image of the iris light to infinity. This light occupies a cylindrical volume infinity space (I think there's a word for this, but I don't know it) for about 6 inches if unmolested, but it is highly divergent - after 6 inches it spreads out rapidly. The condenser is placed within this cylinder where the light inside has a high degree of angular content at any given point. If it's not projected perfectly colinear with the optic axis, that doesn't really matter because the light that should have been 0deg is now 1 deg but the light that was -1deg now becomes 0deg. I guess it could be important for advanced methods like DIC or something, but I don't think it matters much for typical imaging techniques. I think the main thing would be a slight nonuniformity in illumination intensity as a function of angle at the specimen - maybe that would be noticeable in darkfield?

I tried tilting my condenser several degrees below the object plane (I think this is equivalent) and I couldn't tell the difference at all. Even the field iris image looked fine. I've got a BH2 I need to open up to service anyway. Maybe I'll purposefully misalign it before I disassemble and try to see any differences!

I think part of the success of the BH2 and scopes like it is that they're extremely optically forgiving. That makes them easy to build and easy to operate. I'd wager probably half or more of BH2 users never knew of or performed Koehler alignment. When you have a diffuse disk instead of a filament - it's rarely going to cause a major imaging issues!
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Harold
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Re: Collimation of Oly BH2 microscope

#4 Post by Harold » Sat Dec 04, 2021 6:22 pm

Thanks josmann and Debult. Sounds like my suspicion that the influence of off axis light was more or less minimized by the design. If I manage to acquire the bits and piece needed for Carl's alignment procedure, I'll probably give it a try just to satisfy my curiosity. Meantime, I'll continue to enjoy the fine images produced by my BH2 with D and S Plan objectives.

carlh6902
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Re: Collimation of Oly BH2 microscope

#5 Post by carlh6902 » Fri Dec 10, 2021 12:31 am

If you use a modified light inlet barrel as the target, it fits VERY accurately, with no discernable play. It is almost an interference fit. Having said that, you'll never notice the effects if it's out of collimation. But technically, it does matter, if only just a little bit. I've had many people ship just the pillar arm assembly to me, for repair. When they get it back and put it back together, the collimation is almost certainly impaired, but not to the point where it is visible.

Carl
--- If you're in the Kansas City area and you need help with an Olympus BH-2 scope, PM me. I love to work on these things ---

Harold
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Re: Collimation of Oly BH2 microscope

#6 Post by Harold » Fri Dec 10, 2021 12:43 am

carlh6902 wrote:
Fri Dec 10, 2021 12:31 am
If you use a modified light inlet barrel as the target, it fits VERY accurately, with no discernable play. It is almost an interference fit. Having said that, you'll never notice the effects if it's out of collimation. But technically, it does matter, if only just a little bit. I've had many people ship just the pillar arm assembly to me, for repair. When they get it back and put it back together, the collimation is almost certainly impaired, but not to the point where it is visible.

Carl
Carl,
Thanks for chiming in. After a bit of hands on poking and prodding, I got the hint :) In any case, could you help clear up the discussion re: CH and BH2 parts comparability. Specifically, I'm wondering if things like the pinion gear on the right hand fine focus knob from a CH series could be used in a BH2. I "inherited" a BH2 stand that presented with cracked gear. Everything else with it works reasonably well iif badly gummed up. But with a replacement for that pinion, there's no fine focus possible.

cally

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Re: Collimation of Oly BH2 microscope

#7 Post by carlh6902 » Fri Dec 10, 2021 1:45 am

Alan Wood has the CH repair manual from Olympus, in PDF format, on his site. It clearly shows the AA7826 gear used in the knob. I can verify that it is the same gear as the BHS, BHT, BHSU, and BHTU (and others).

Carl
--- If you're in the Kansas City area and you need help with an Olympus BH-2 scope, PM me. I love to work on these things ---

Harold
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Re: Collimation of Oly BH2 microscope

#8 Post by Harold » Fri Dec 10, 2021 2:22 am

Again, many thanks. Now if I can just find a right side fine focus knob with the AA7826 on it. I suspect the only way to do that is also buying whatever comes "attached".

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