Kohler Trouble

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mneium
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Kohler Trouble

#1 Post by mneium » Sat Apr 04, 2020 10:58 pm

Howdy. I recently bought an Olympus BH2 (BHS). I read the manual and the Kohler illumination does not seem to be working as the literature indicates it should. It's making me lose my hair.

Basically the image only ever looks good if I completely close the condenser, all the way to 0.15NA. This is the case at both low and high magnifications.
The contrast and "depth" goes away if I open the condenser's iris up to the recommended value of 65-85% of the objective's NA:

Images taken with Olympus Plan Apo 10X, 0.70NA
https://i.imgur.com/moKbKkw.jpg < condenser raised to slide 100%, field iris opened to just outside of view field, condenser iris 100% closed (0.15NA)
https://i.imgur.com/cUktxaN.jpg < condenser raised to slide 100%, field iris opened to just outside of view field, condenser iris open to 0.6NA. It looks similar to this until I go down to about 0.25NA


Additionally, I am unable to get an "image" of the field iris (by moving the condenser up or down) like the manual says I should start by doing.
The closest I can get is by moving the condenser all the way up so it's nearly touching the slide. As I raise it, I can see the image of two pieces of glass in the field iris optics - I can see dust and inclusions on them. First the upper (external) piece of glass, then an internal one. But I can never see the field iris itself. It seems to stop short of it. This is what it looks like with the condenser fully raised: https://i.imgur.com/7IblgHD.jpg


The image of the field iris grows a little sharper if I use immersion oil on the condenser, but it never becomes fully sharp.



Besides user error, I have two potential theories on what's wrong:
1) Maybe it came with the wrong condenser, or one that is broken somehow: https://i.imgur.com/0OrsmDo.jpg

All the other BH2-AAC condensers I've seen seem to have black tops, not this white one. I did see one BH2-AAC in Google Images that had a white top, but it could have been mis-identified by the owner. Perhaps this condenser is meant for a BX microscope and is optically incompatible with the BH-2?

This condenser does not fit perfectly in the BH-2 dovetail and requires a small shim at the back of the dovetail to center it (without the shim, the centering screws go in the wrong direction to get it centered, so to speak.) I don't have an Abbe condenser on-hand to test this theory.

2) Maybe the internal lenses in the base were knocked out of calibration during shipping (it was not packed super-securely.)

Any ideas, fellows?

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Re: Kohler Trouble

#2 Post by MicroBob » Sun Apr 05, 2020 1:24 am

Hi,
your insect wing has quite a depth and it is not possible to have it sharp top to botton at the same time and maintain the full resolution. You probably have seen great images of insects, these are made with a fairly wide opened condenser aperture from a stack of lots of images. The images are calcutated into one immage by means of an image stacking software like Picolay or Helicon focus.
The image of your field aperture is quite okay when the condenser is close to the slide in this setting. Perhaps your condenser is intended for a different stand that has a slightly longer distance from slide underside to field aperture. This is a fine condenser though and it won't harm that it doesn't quite get a sharp image of the field amperture. A simple Abbe condenser doesn't offer more in the optimal setting.

Bob

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Re: Kohler Trouble

#3 Post by deBult » Sun Apr 05, 2020 3:07 am

The AAC condenser is one of the best Olympus condensers ever.

The white top is for helping out locating low contrast samples and is missing in most 2nd hand samples.

To expand on Bob’s input: start with a thin flat subject when Köhler-ing: a stage micrometer, a plant microtome cut.
this should be focussed first, then start the Kohler procedure.

To enjoy the resolution these high NA plan-apo objectives bring, you need the condenser NA match the NA of the objective.
So for high resolution you need to open up the diaphragm. This is always a balancing act between image contrast plus more depth if field (diaphragm closed), high resolution And less depth of field (open diaphragm) [and flare when opening up to much using older - uncoated - glass].

Please let us know the results.


Best, deBult (relative beginner, with a BH2)

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Re: Kohler Trouble

#4 Post by deBult » Sun Apr 05, 2020 4:35 am

Forgot to mention the AAC condenser is no good match to low power objectives (1-2-4*).

You will not be able to Kohler those.

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Re: Kohler Trouble

#5 Post by 75RR » Sun Apr 05, 2020 5:30 am

Some important points to look out for are :

a.) Make sure the condenser is correctly seated.

b.) Condenser lens does need to be very nearly touching the slide - we are talking a couple of mm

c.) a much flatter subject with a cover glass on top.
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Re: Kohler Trouble

#6 Post by Hobbyst46 » Sun Apr 05, 2020 5:53 am

deBult wrote:
Sun Apr 05, 2020 4:35 am
Forgot to mention the AAC condenser is no good match to low power objectives (1-2-4*).

You will not be able to Kohler those.
Yes. The achromat BH2 condenser that I know of has a flip-out front lens. That is flipped out for the 4X and 10X objectives.
Alternatively, a separate auxiliary lens beneath the condenser serves for the low mags. At least, this has been the case with older Olympus microscopes, e.g. Vanox.
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Re: Kohler Trouble

#7 Post by mneium » Sun Apr 05, 2020 12:21 pm

Hey all, and thanks for the advice

I took some images at 60X oil with an Olympus Plan Apo 60X 1.4NA. Both the condenser and objective are oiled to the slide here.

The subject is a drop of milk with a #1.5 coverslip on. I suppose the little nodules are milk fat.

In all images the condenser is raised 100%, the field iris is nearly 100% closed (to just outside the objective radius) and the halogen lamp is at its lowest power setting
https://i.imgur.com/0OcUvVK.jpg < Condenser closed 100% (to 0.15NA)
https://i.imgur.com/AwiVqo6.jpg < Condenser open 50% (to 0.7NA)
https://i.imgur.com/00sA82P.jpg < Condenser open 90% (to 1.2NA)

Is this really normal? The image just gets nearly indistinguishable if I open the condenser past its most-closed position. It seems as if there is far too much light, and things become blurry - someone earlier mentioned flare can be caused by a bad AR coating. There are some marks in the AR coating on this condenser (but not the glass itself,) could it be due to this? https://i.imgur.com/6EKfjtL.jpg

I am able to get an image of the field iris by raising the condenser a little bit within the dovetail with my fingers, but the image does not improve at all when I do this.

I should say BTW that although I can see the iris at the field diaphragm, the light that is coming out of the diaphragm is not a collimated shaft of light:
https://i.imgur.com/lqIInjg.jpg < Field iris at lowest halogen bulb setting
https://i.imgur.com/AJ1RWUS.jpg < Highest setting (can see some dust in the optics)
https://i.imgur.com/MAtqxQ9.jpg < Paper on top at highest setting

Dunno if that's typical.
Last edited by mneium on Sun Apr 05, 2020 3:54 pm, edited 1 time in total.

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Re: Kohler Trouble

#8 Post by Hobbyst46 » Sun Apr 05, 2020 1:18 pm

mneium wrote:
Sun Apr 05, 2020 12:21 pm
In all images the condenser is raised 100%, the field iris is nearly 100% closed (to just outside the objective radius) and the halogen lamp is at its lowest power setting
https://i.imgur.com/0OcUvVK.jpg < Condenser closed 100% (to 0.15NA)
https://i.imgur.com/AwiVqo6.jpg < Condenser open 50% (to 0.7NA)
https://i.imgur.com/00sA82P.jpg < Condenser open 90% (to 1.2NA)
1. Usually the halogen lamp should be at a high power setting, not the lowest. Especially for high-mag objectives such as the 60X.
2. Illumination is not even. Either an air bubble in the immersion oil, and/or the condenser is not centered. careful centration increases the brightness across the field of view.
3. The condenser iris itself functions properly here - it increases the contrast. Hence you can see the fat particles when it is closed.
Hopefully these help some.
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Re: Kohler Trouble

#9 Post by 75RR » Sun Apr 05, 2020 1:28 pm

Perhaps some more photos of your microscope might help.

Can you take another photo similar to this one: https://i.imgur.com/MAtqxQ9.jpg but with the iris half closed?

Can you remove the condenser and photograph it so we can see its iris and lenses?

Lastly, a photo from the side of your microscope
Last edited by 75RR on Sun Apr 05, 2020 1:32 pm, edited 1 time in total.
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Re: Kohler Trouble

#10 Post by BramHuntingNematodes » Sun Apr 05, 2020 1:32 pm

How does it look through the eyepiece with just your eyeball? Some cameras need to have the exposure set way down to produce a usable image.
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Re: Kohler Trouble

#11 Post by mneium » Sun Apr 05, 2020 1:33 pm

Hobbyst46 wrote:
Sun Apr 05, 2020 1:18 pm
mneium wrote:
Sun Apr 05, 2020 12:21 pm
In all images the condenser is raised 100%, the field iris is nearly 100% closed (to just outside the objective radius) and the halogen lamp is at its lowest power setting
https://i.imgur.com/0OcUvVK.jpg < Condenser closed 100% (to 0.15NA)
https://i.imgur.com/AwiVqo6.jpg < Condenser open 50% (to 0.7NA)
https://i.imgur.com/00sA82P.jpg < Condenser open 90% (to 1.2NA)
1. Usually the halogen lamp should be at a high power setting, not the lowest. Especially for high-mag objectives such as the 60X.
2. Illumination is not even. Either an air bubble in the immersion oil, and/or the condenser is not centered. careful centration increases the brightness across the field of view.
3. The condenser iris itself functions properly here - it increases the contrast. Hence you can see the fat particles when it is closed.
Hopefully these help some.
>1. Usually the halogen lamp should be at a high power setting, not the lowest. Especially for high-mag objectives such as the 60X.
I see. But the viewfield becomes terrible at the highest setting. Way too much light..
>2. Illumination is not even. Either an air bubble in the immersion oil, and/or the condenser is not centered. careful centration increases the brightness across the field of view.
It seems that the condenser is tilted slightly within the dovetail because of the shim I had to use to get it centered. This can be fixed. But, trying just now, it doesn't reduce the insane amount of glare/flare that I experience when the condenser is opened.
>3. The condenser iris itself functions properly here - it increases the contrast. Hence you can see the fat particles when it is closed.
But shouldn't the image look acceptable when the condenser is somewhat opened? The manual recommends you open the condenser to 65-80% of the objective's NA. When I do that, the image becomes extremely bad.

I cannot shake the feeling that something is very off here? It doesn't seem normal that the image is awful except when the condenser is 100% closed.
BramHuntingNematodes wrote:
Sun Apr 05, 2020 1:32 pm
How does it look through the eyepiece with just your eyeball? Some cameras need to have the exposure set way down to produce a usable image.
It actually looks worse than it does through the camera. Very blurry and "overexposed", as if there is a lot of stray light. Can hardly make out anything.

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Re: Kohler Trouble

#12 Post by deBult » Sun Apr 05, 2020 1:41 pm

Not sure what is so “horrible” about the 90% picture?

And yes the lightning is uneven: please share some pictures of you setup.

As stated earlier you cannot have BOTH high resolution AND high contrast.

Thats where the coloring of samples comes in and/or the advanced lighting techniques (oblique, Rheinberg, phase contrast etc).

Best deBult

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Re: Kohler Trouble

#13 Post by mneium » Sun Apr 05, 2020 2:02 pm

75RR wrote:
Sun Apr 05, 2020 1:28 pm
Perhaps some more photos of your microscope might help.

Can you take another photo similar to this one: https://i.imgur.com/MAtqxQ9.jpg but with the iris half closed?

Can you remove the condenser and photograph it so we can see its iris and lenses?

Lastly, a photo from the side of your microscope

https://i.imgur.com/Q0qdZGT.jpg < Field iris 100% closed
https://i.imgur.com/wKllU8e.jpg < 50% closed
https://i.imgur.com/h3wNoZ4.jpg < 0% closed

https://i.imgur.com/YVbLb2C.jpg < Condenser iris 100% closed
https://i.imgur.com/bLWoAPz.jpg < 0% closed
https://i.imgur.com/mWC6hQr.jpg < front lens

https://i.imgur.com/hBz1cBp.jpg < microscope side shot

@all: Are the images you've seen so far really typical? Turning the halogen lamp up to 50% with the condenser opened to the manual's stated correct position (65-85% of the objective's NA, so condenser opened to .6 NA for the 10X like in the first post) makes the image look unbearably bright and flare-filled - like eye damage levels of bright. With the lamp turned down all the way it can be looked at, but is still filled with flare and very blurry.

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Re: Kohler Trouble

#14 Post by 75RR » Sun Apr 05, 2020 2:36 pm

Your stage does not look horizontal, if it isn't, then that could account for the fact that you can not see the field iris in focus - as the sample would be too far away from the top lens of the condenser.
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Re: Kohler Trouble

#15 Post by mneium » Sun Apr 05, 2020 3:50 pm

I was able to get an image of the field iris by shimming the condenser's front part slightly upwards with a piece of paper.
But it still seems like there is way, way too much stray light, tons of blur, etc. at the recommended condenser settings. And no matter how the condenser is set, turning up the halogen bulb past the minimum setting makes the image unbearably bright.

This is depressing. I can't tell if the problem is with the condenser or the microscope or what.

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Re: Kohler Trouble

#16 Post by 75RR » Sun Apr 05, 2020 4:06 pm

Check the stage is level first. That is important.

You might want to open the lamphouse and have a look inside. Perhaps takes a photo of the bulb.
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Re: Kohler Trouble

#17 Post by mneium » Sun Apr 05, 2020 4:30 pm

75RR wrote:
Sun Apr 05, 2020 4:06 pm
Check the stage is level first. That is important.

You might want to open the lamphouse and have a look inside. Perhaps takes a photo of the bulb.
Stage is definitely not 100% level, I can see it is canted slightly toward the back: https://i.imgur.com/QLNA0Aq.jpg
Actually, when I first unpacked the scope I noticed the stage wobbled up and down a little bit, the screw that goes into the dovetail did not seem to fully make contact (or it makes contact too high? https://i.imgur.com/sb4jELp.jpg) so I shoved a piece of cloth between the screw and dovetail to make the contact more flush. With that, it doesn't wobble, but it's still tilted slightly towards the back. Not sure what to do about this. Perhaps the stage holder is attached wrongly?

Here's the bulb:
https://i.imgur.com/67ZtcVo.jpg
https://i.imgur.com/mhgkC9o.jpg

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Re: Kohler Trouble

#18 Post by Roldorf » Sun Apr 05, 2020 4:47 pm

Maybe you have some parts missing from under the stage.

Here is the repair manual for the BH-2 (BHS) (with parts drawings).

http://www.alanwood.net/downloads/olymp ... ual-lq.pdf
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Re: Kohler Trouble

#19 Post by 75RR » Sun Apr 05, 2020 4:48 pm

I recommend that you sort the stage out first

One of the bonuses of owning an Olympus BH2 are the amazingly detailed repair manuals made by forum member Carl Hunsinger

This one is for the stage, though all you hopefully need to do is lock it in correctly: http://www.alanwood.net/downloads/olymp ... -rev-2.pdf

and a few more: http://www.alanwood.net/photography/oly ... loads.html


As to the lamphouse, was wondering if perhaps it had been converted to a very bright LED or worse yet if it was Mercury. The good news is that it is a Halogen - so your eyesight is safe!


The two yellow lines are parallel - that has got to be 3mm+ which is a huge slope.
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Re: Kohler Trouble

#20 Post by Roldorf » Sun Apr 05, 2020 5:05 pm

Here is also a user manual on how to adjust the stage.

http://www.alanwood.net/downloads/olymp ... manual.pdf

Hope it helps.
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Re: Kohler Trouble

#21 Post by mneium » Sun Apr 05, 2020 5:12 pm

Thanks for the manuals - will give them a read over.

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Re: Kohler Trouble

#22 Post by MichaelG. » Sun Apr 05, 2020 6:05 pm

mneium wrote:
Sun Apr 05, 2020 4:30 pm
Here's the bulb:
https://i.imgur.com/67ZtcVo.jpg
https://i.imgur.com/mhgkC9o.jpg
Excellent images of the bulb; but I can’t see the rating [Volts and Watts]
... numbers are usually printed on them.

These halogen lamps all look very similar ...
Is it possible that the previous owner fitted the wrong bulb ??

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Re: Kohler Trouble

#23 Post by 75RR » Sun Apr 05, 2020 6:46 pm

MichaelG. wrote:
Sun Apr 05, 2020 6:05 pm
mneium wrote:
Sun Apr 05, 2020 4:30 pm
Here's the bulb:
https://i.imgur.com/67ZtcVo.jpg
https://i.imgur.com/mhgkC9o.jpg
Excellent images of the bulb; but I can’t see the rating [Volts and Watts]
... numbers are usually printed on them.

These halogen lamps all look very similar ...
Is it possible that the previous owner fitted the wrong bulb ??

MichaelG.
I can't see the wattage - it is supposed to be 100w - perhaps someone else can ...
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Re: Kohler Trouble

#24 Post by Hobbyst46 » Sun Apr 05, 2020 6:54 pm

MichaelG. wrote:
Sun Apr 05, 2020 6:05 pm
mneium wrote:
Sun Apr 05, 2020 4:30 pm
Here's the bulb:
https://i.imgur.com/67ZtcVo.jpg
https://i.imgur.com/mhgkC9o.jpg
Excellent images of the bulb; but I can’t see the rating [Volts and Watts]
... numbers are usually printed on them.

These halogen lamps all look very similar ...
Is it possible that the previous owner fitted the wrong bulb ??

MichaelG.
Michael's question might be highly relevant. The wattage must be limited to some value, otherwise heat will deform and ruin the base. This happened to me once: a repair guy replaced a 20W halogen bulb in the base of my VMZ scope with a 50W bulb. I only discovered it after the damage was beyond repair.
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Re: Kohler Trouble

#25 Post by mneium » Sun Apr 05, 2020 6:55 pm

I gave the bulb a closer look, it's a Philips 12v100w. Seems right on for the BHS.
I have two OEM Olympus 12v100W coming anyway, will give them a try but I doubt that's the source of the flare/blur issue when the condenser is open

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Re: Kohler Trouble

#26 Post by 75RR » Sun Apr 05, 2020 7:00 pm

If it is not a higher rated (than it should be) halogen bulb perhaps it is just missing an ND (Neutral Density) filter?
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Re: Kohler Trouble

#27 Post by MichaelG. » Sun Apr 05, 2020 7:06 pm

mneium wrote:
Sun Apr 05, 2020 6:55 pm
I gave the bulb a closer look, it's a Philips 12v100w. Seems right on for the BHS.
Well that’s one off the list of possibilities
... Always worth checking such things though.

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Re: Kohler Trouble

#28 Post by mneium » Sun Apr 05, 2020 7:10 pm

75RR wrote:
Sun Apr 05, 2020 7:00 pm
If it is not a higher rated (than it should be) halogen bulb perhaps it is just missing an ND (Neutral Density) filter?
There is indeed no filter (though I have the filter holder.)
Should I get one? I didn't know they were needed.

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Re: Kohler Trouble

#29 Post by 75RR » Sun Apr 05, 2020 7:54 pm

Don't own an Olympus BH2, but as a 12v 100 watt Halogen puts out a lot of light (particularly as in order to maintain/extend bulb life it should be kept within a 9-11 volt range),

it would make sense that it should have an ND filter for most observations and that it be removed for say high magnification DIC and Darkfield.

Perhaps an actual BH2 owner, and there are several on the forum, can confirm. I am sure mneium will sleep better for it.
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Re: Kohler Trouble

#30 Post by photomicro » Mon Apr 06, 2020 2:18 pm

75RR wrote:
Sun Apr 05, 2020 7:54 pm
Don't own an Olympus BH2, but as a 12v 100 watt Halogen puts out a lot of light (particularly as in order to maintain/extend bulb life it should be kept within a 9-11 volt range),

it would make sense that it should have an ND filter for most observations and that it be removed for say high magnification DIC and Darkfield.

Perhaps an actual BH2 owner, and there are several on the forum, can confirm. I am sure mneium will sleep better for it.
It seems to me that much of this is conjecture in terms of contributing in a major way to the lack of a decent image, and that what mneium really must do *first* is sort that stage out, ie. get it level.

Surely, not only will that be the reason of the plane of focus issues, but also probably why the lighting *seems* misaligned.

I am assuming that the stage fits with some sort of dove-tail.

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