Olympus U-DICT versus U-DICTS

[microb]

I have U-DICT slides, but for the U-DICTS which has not only a rotating knob but also a "lateral adjustment" shift hence the S.

So some objectives have back focal planes at -19.1mm and some are at -25.0mm.

So the pull lever, I believe, in Normal (pulled out) has the prism raised 6.1mm. For BFP1, pushed in, it's at the bottom allowing the prism to reach 25mm in depth for higher resolution objectives.

Could someone diagram or confirm what the S actually does with the prism adjustment?

The one pictured is on e-bay right now. But I'd like to hold off on buying one until I can accurately measure back focal plane distances with DICs. Then maybe I can just send someone a rig to measure, and start getting numbers for prisms that I don't have like the K Leica series. I'd like to get numbers for that for the DMRs I have.

[microb]

In the one ebay side picture, it looks like a vertical track, so the slider lever must wedge the prism up to the top.

Any diagrams and measurements would be appreciated just to get an idea. I assume at some point I'll have to buy one.

[viktor j nilsson]

Could it be that it tilts the prism a couple degrees relative to the optical axis? I remember you posted a link to an Olympus patent on this exact thing: that when you tilt the prism, the location of the Interference fringe shifts, and can thus match objectives with different BFPs.



Patent:
https://patents.google.com/patent/US20010040723A1

Our earlier discussion:
viewtopic.php?f=5&t=9032

[hans]

From the linked earlier discussion:

John, do you have any idea how large the angle theta can be before it starts to seriously degrades image quality? In theory I could move the default position of the objevtive prism even higher up than it is now, which could help me get DIC with my 4x objectives as well. However, this would require a rather large angle theta of 22* when using my 60x planapo. I have a feeling that this might be too much.

No idea if some more subtle effects related to birefringence could be limiting, but for simple plane parallel plate effects this summary gives some approximations with examples plotted:
Wyant, Creath - Basic Wavefront Aberration Theory for Optical Metrology
https://www.researchgate.net/publicatio ... _Metrology

For large tilt angles it seems like astigmatism (quadratic in tilt angle) would probably be dominant:

[microb]

I hadn't noticed it before, but isn't the patent diagram wrong? Shouldn't the optical axis of the Nomarski prisms mirror each other?

The wedge with the axis pointing out of the drawing should be the top wedge for the objective prism and be the bottom wedge for the condenser prism.

The figures show the prisms ordered the same way, not flipped to oppose each other.

[microb]

So does the U-DICTS centered knob (unlike the U-DICT screw which moves the prism in and out) rotate the prism? And the side lever moves the assembly in and out?

I don't have a U-DICTS slide to check that.

[viktor j nilsson]

I believe you are correct. It should be looking like this:



I find that schematics of DIC setups are very often drawn inocorrectly.

[microb]

Is rotating the top prism on the vertical axis like this still a valid set up?

Come to think of it, the condenser discs can rotate freely, so the top prism, even though it's locked in a slider could rotate that way too.

[viktor j nilsson]

So does the U-DICTS centered knob (unlike the U-DICT screw which moves the prism in and out) rotate the prism? And the side lever moves the assembly in and out?

I don't have a U-DICTS slide to check that.

I would assume that the centered knob translates the prism in and out, and the side lever lifts the prism up on one side so that it becomes angled. The "BFP1->Normal" suggests that the lever is used to match different Back Focal Planes.

[viktor j nilsson]

Is rotating the top prism on the vertical axis like this still a valid set up?

Come to think of it, the condenser discs can rotate freely, so the top prism, even though it's locked in a slider could rotate that way too.

Sorry, I'm not sure what you are saying here. This is the situation you are after:

[microb]

Sorry, I'm not sure what you are saying here. This is the situation you are after:

If you look at the green box above, note the outward pointing optical axis is on the left not the right as in the original. Technically I guess a rotation would make the green box have the optical axis point in, but the OA is symmetric so that doesn't matter.

Basically jam the U-DICT in backwards into he objective turret slot. You can't but let's assume it would fit that way. It should give the same image.

[viktor j nilsson]

Sorry, I'm not sure what you are saying here. This is the situation you are after:

If you look at the green box above, note the outward pointing optical axis is on the left not the right as in the original. Technically I guess a rotation would make the green box have the optical axis point in, but the OA is symmetric so that doesn't matter.

Basically jam the U-DICT in backwards into he objective turret slot. You can't but let's assume it would fit that way. It should give the same image.

Now I see what you did. I was confused by the fact that we were talking about different rotations.

And no, I do not think that it would give the same image. I have been playing a lot with my loose prisms, flipping them upside down and forward-backwards. I can definitely say that both types of rotations make a big difference. For any combination that works, it is only one of the four possible orientations that gives true DIC. One of the other orientations may be close, and that's usually when you flip it upside down, if I remember correctly. But flipping it so that it is inserted backwards becomes way off and results in a BFP with a large number of narrow interference stripes.

[microb]

One of the other orientations may be close, and that's usually when you flip it upside down, if I remember correctly. But flipping it so that it is inserted backwards becomes way off and results in a BFP with a large number of narrow interference stripes.

But the condenser prism are in a ring. They can be put in at any rotation around the optical path/transmission axis. I thought that would mean the objective slide could be treated the same way, especially if it were not angled in the slide, which the Olympus ones are, so those would need some tweaking if it could be spun around.

[viktor j nilsson]

I believe the condenser prisms has a pin that fits in a groove or hole, which ensures that they are positioned the right way, no?

[microb]

I believe the condenser prisms has a pin that fits in a groove or hole, which ensures that they are positioned the right way, no?

You're right. I should have just looked. That answers my questions. I had mentally painted myself into a corner there, but yes there is an alignment pin. For some reason I was thinking it was only on the analyzer.

Anyway, that was this morning's brain fart. I should have remembered with the polarizer not moving that my thought of the disc being able to rotate made no sense. So I guess that diversion aside, the original notion was that could one 180 the U-DICT slide and still get a valid image. So for that, the bottom part of the wedge with the angled optical axis would not be symmetric as it would not match up with the extraordinary and normal rays coming up flipped. So 180 wouldn't work either.

[hkv]

I have the DICT-S. I have never noticed any difference in the image quality based on the position of the BFP switch. It looks equally good in either position, at least for my objectives. Some of these require the level in a pushed in position according to the specs. Let me know if you want me to measure or investigate something specific on it.

[viktor j nilsson]

I have the DICT-S. I have never noticed any difference in the image quality based on the position of the BFP switch. It looks equally good in either position, at least for my objectives. Some of these require the level in a pushed in position according to the specs. Let me know if you want me to measure or investigate something specific on it.

Interesting to hear that you don't notice any difference, Håkan. So the BFP switch gets pushed in or pulled out? Can you tell what happens with the prism when you operate the switch? Does it tilt the prism?

I have done some sloppy tests with my DIY setup, and I too did not see a marked difference in image quality when I tilted the prisms -10 to +10 degrees or so. But I really should do some more careful tests at some point.

[hkv]

I have the DICT-S. I have never noticed any difference in the image quality based on the position of the BFP switch. It looks equally good in either position, at least for my objectives. Some of these require the level in a pushed in position according to the specs. Let me know if you want me to measure or investigate something specific on it.

Interesting to hear that you don't notice any difference, Håkan. So the BFP switch gets pushed in or pulled out? Can you tell what happens with the prism when you operate the switch? Does it tilt the prism?

I have done some sloppy tests with my DIY setup, and I too did not see a marked difference in image quality when I tilted the prisms -10 to +10 degrees or so. But I really should do some more careful tests at some point.

Yes, you pull or push that rod. It does not twist. I checked what happens. It moves the DIC prism straight up or down by a maybe 5-6 mm. I guess to compensate for the different back focal plane positions.

[microb]

Yes, you pull or push that rod. It does not twist. I checked what happens. It moves the DIC prism straight up or down by a maybe 5-6 mm. I guess to compensate for the different back focal plane positions.

Thanks.