Another LOMO condenser issue

[Crater Eddie]

I know this is long winded, sorry.
Recent threads about condensers have reminded me of an issue I have with Boris, my big Russian scope, Biolam L-2-2 (its easier to just say Boris). You can see a few old photos here:

viewtopic.php?f=24&t=710

I have never been able to get the field diaphragm in focus on any objective over 10x, and the 10x just barely focuses at the top end of the condenser travel. With higher power objectives the focus is somewhere above the bottom of the slide. If I remove the slide I can get it to focus at least with a 20x objective, didn't try anything higher as there was no point. I get the same results whether using the short objectives or the long barrel ones, LOMO or otherwise. There is a thick frosted swing-out lens under the condenser, I'll often experiment with this lens in or out to get the best image. This is an actual lens, not just a filter, and yes, the lens itself is frosted.
The illumination system is partly built into the base and partly sticking out the back, but is very similar to the LOMO OI-35, for which I do have a sort-of manual. The condenser is the LOMO KOH-1K oblique condenser, for which I can find little info online. It is very similar to the OI-14, but the top lens is removable... the one I have is marked 1.25 whereas the OI-14 is 1.4. I have seen a few of the 1.25 removable lenses on $bay, have never seen a different one. If I substitute the LOMO C-BF standard condenser, then I can focus the field diaphragm using higher power objectives, although the focus gets very soft at the higher powers.
Boris and his ilk seem to be fairly uncommon, though I do find a few photos of them on Russian sites. Many seem to have this same condenser, or perhaps the OI-14, mounted.
If anyone knows anything about the KOH-1K condenser, I'm all ears. Would it be worth replacing it with an OI-14? They don't seem to be free. I could operate with the C-BF, but then I loose the nifty oblique capability. There are other condensers available for this stand, I have not had the opportunity to play with any of them.
As always, all comments and suggestions appreciated.
CE

[Brad_]

It sounds like your big LOMO's lamp is sending a parallel light
beam, as if from infinity, to the condenser. The BFO-C condenser
expects a diverging light beam, as if from 10 inches.

The late Mr. Sterrenburg explains it nicely here:

http://www.microscopy-uk.org.uk/primer/illumin.htm

I doubt there is much you can do. Fiddling with a negative lens
under the stage might be interesting. What is that swing out
component beneath the stage, a negative lens?

If you can get the oblique condenser working *and* if it takes
your trinocular head *and* if it can take the stubby little 33mm
*and* 45mm objectives you will have a true treasure. The el
cheapo phase and dark field condensers will work and you'll be
off and running.

Keep us informed.

Have fun.

[mrsonchus]

Hi Eddie- interesting and familiar scenario - exactly the one I'm experiencing with my Orthoplan.

[Crater Eddie]

Brad,

You are correct, the standard C-BF condenser is normally used in scopes that have the lamp directly below it.
It turns out that the MFN-11 trinoc does work well with this scope. Actually I now have the US marketed HT-30 trinoc on it, it works well. I get good images both with the shorty objectives and long barrel objectives, so I think I'm good there. If I can just get this condenser issue sorted I'll be good to go. This same stand was often built up as a polarizing scope, there were apparently a couple of different condensers available for that. I have been considering getting one of those to play with if I can't make any headway with what I have.
The best I can recall, I think the swing-out lens is a frosted positive lens. I'll double check that tonight when I get home.
Thanks for the link, I'll read over that.

Mrsonchus,

It was your thread about your condenser issues that prompted me to outline my issues here, as you seem to be making some headway.

CE

[mrsonchus]

Yes, it's a problem - the above link to the article has some really interesting points re the critical vs Kohler situations, and mentions the 'frosted lamp collector' situation which seems to be the thing that prevents achievement of a 'truly Kohler' sharp field iris.
I'm going to have to have a good pick through this tonight as there's a lot to consider....

A very tricky and interesting situation for sure!

[Crater Eddie]

Here are a couple of views of the condenser and a closeup of the swing-out lens, which is indeed a frosted positive lens.
CE

[Crater Eddie]

Actually, if we could see the lens edge-on, it looks quite pyramidal, more or less like this.
CE

[Brad_]

How strange. It must be for filling the field of a low power
objective but why go through the trouble of grinding such a
substantial lump of glass, accurately mounting it and then
frosting it?

You might want to get on the Yahoo group "Microscope" A Russian
fellow, Dushan I believe, used to lurk there. He's an expert on
all things LOMO. If you compose an interesting subject line with
LOMO in it he's sure to pounce -- if he's still hanging around.

Have fun.

Brad

[Crater Eddie]

It must be for filling the field of a low power objective

That's what I always assumed it was for. It works fine for that, and has proven useful at other times as well.
I am a member of the Yahoo group, though I don't look at it very often. I might ask there. Thanks
CE

[Crater Eddie]

A very helpful fellow over on the Microscope Yahoo group suggested that I check that the condenser was traveling up as close to the slide as possible. I was certain that I had done this long ago, but I went ahead and double checked... and found that the travel stop was set just a fraction of a smidgen too low. I think the actual scientific unit of measurement is "a quarter of a frog hair".
Careful adjustment of the stop has the problem solved. Mind you, I don't get a real sharp focus of the field diaphragm at higher powers, but it comes to "best focus" and out again, so now I can get it where it needs to be.
It just goes to show that the simplest solution is often the correct one. And even if you are certain that you have checked something, go ahead and check it again anyway.
I feel pretty dumb about the whole thing, but had to give the solution here for closure.
Thanks to all who contributed.
CE

[75RR]

It just goes to show that the simplest solution is often the correct one.

They tend to be cheaper too, so I am all for them. :)

[zzffnn]

Thank you for the update and I am glad you solved the problem yourself. I remember David Walker said his Biolam had the condenser set too low for high NA darkfield, he changed a set screw to raise it and solved the problem.

[mrsonchus]

A very helpful fellow over on the Microscope Yahoo group suggested that I check that the condenser was traveling up as close to the slide as possible. I was certain that I had done this long ago, but I went ahead and double checked... and found that the travel stop was set just a fraction of a smidgen too low. I think the actual scientific unit of measurement is "a quarter of a frog hair".
Careful adjustment of the stop has the problem solved. Mind you, I don't get a real sharp focus of the field diaphragm at higher powers, but it comes to "best focus" and out again, so now I can get it where it needs to be.
It just goes to show that the simplest solution is often the correct one. And even if you are certain that you have checked something, go ahead and check it again anyway.
I feel pretty dumb about the whole thing, but had to give the solution here for closure.
Thanks to all who contributed.
CE

Handy thread - I'm going to check this also - it's obviously a critical setting - thanks for the thread and update.

[mrsonchus]

By the way Eddie - I have decided to give you the 'Gold Cup Award For Assistance' - your information re the increase of the maximum height of your condenser - how it has given you a focused field-iris even to the extent of being able to go 'through t\he point of sharpness':

I just a minute ago adjusted my Orthoplan's max condenser height - it was already easily within about 0.2mm of the slide's under-side, and I've also read but can't remember where as I'm almost boggle-eyed with reading about condenser-optics and practicalities, that "any condenser found to be more than 0.5mm away from the slide at it's maximum height is very probably incorrectly set" - and assumed as mine was well within this that all was well.....

I was wrong, very wrong, and it's only thanks to your recent post that I decided to adjust it even closer - in fact it nips a cigarette-paper now as it's fully raised - I'd say it's no more that about 0.04mm at most from the slide at it's maximum - probably half of this - I'll get a feeler-gauge in there when I get a minute!

Behold! I've got my Kohler back - sharply focused field iris, which fills the field of view even without the K4 (partly at this time) in place. This is with all objectives so far, the x10 - update - the x10 doesn't quite fill - the K4 in place partly (as I've got to sort the protruding screw problem to allow it to fit fully and to fill the Orthoplan's wide filled), the x40, x50W and the x63 - haven't yet tried my two Oel objectives yet (the x100 and the x54) - but they're very likely indeed to be fine!

So Mr Crater - as far as I'm concerned you are King of the Universe - well at least until tomorrow anyway!

I'm hovering around the house now with a beatific grin and humming gently - even the dog's staying away!

I'll put this little adventure into a proper post tomorrow - we're away again for a week in beautiful Wensleydale tomorrow - but this time I'm taking my lovely stereo 'scope and a full 'taxonomy and specimen kit'!

Thank you a 100 times old chap - you have made me very happy and others really must see this piece of advice - you will help a lot of confused folk with this one Eddie..

Back soon.

[Crater Eddie]

Thanks John, but if anyone deserves credit for the actual fix, it should be David Walker of Micscape Magazine fame, it was he who very kindly suggested that my condenser likely wasn't going up far enough. At least I'm pretty sure that's who it was, he just signed as "David", but I can put 2 and 2 together.
Anyway, I'm very glad that you got your problem solved. I hope we get to see the results sometime soon.
CE

[mrsonchus]

Thanks John, but if anyone deserves credit for the actual fix, it should be David Walker of Micscape Magazine fame, it was he who very kindly suggested that my condenser likely wasn't going up far enough. At least I'm pretty sure that's who it was, he just signed as "David", but I can put 2 and 2 together.
Anyway, I'm very glad that you got your problem solved. I hope we get to see the results sometime soon.
CE

Haha Edddie! My new motto - "if in doubt, say it was 75'"....

As you said, it's amazing, perhaps a feature of the high-end equipment, that their correct adjustment and therefore proper use can sometimes be a matter of microns of tolerance! I will sleep a happy man tonight!

[mrlowndes]

Thanks John, but if anyone deserves credit for the actual fix, it should be David Walker of Micscape Magazine fame, it was he who very kindly suggested that my condenser likely wasn't going up far enough. At least I'm pretty sure that's who it was, he just signed as "David", but I can put 2 and 2 together.
Anyway, I'm very glad that you got your problem solved. I hope we get to see the results sometime soon.
CE

Hey Crater Eddie,

I know this is an old post, but would you be interested in selling your KOH 1K - 1.25 condenser?

[Crater Eddie]

Hey Crater Eddie,

I know this is an old post, but would you be interested in selling your KOH 1K - 1.25 condenser?

Thanks for your interest, but at the moment none of my LOMO stuff is for sale. I hope you find one.

CE