Interference Plane

Everything relating to microscopy hardware: Objectives, eyepieces, lamps and more.
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microb
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Interference Plane

#1 Post by microb » Tue May 26, 2020 8:54 pm

Is the interference plane of an objective usually just inside, as in just below the threads? Phase contrast have the rings there and there are also Hoffman objectives that add blockers and masking there too.

Can one put a Bertrand-like lens between camera and objective, have it aimed at the interference plane, then at the lens's other side at a focal distance away put Hoffman or phase contrast masks? Another lens would then switch it back to infinity focus.

So it might be an achromat doublet positioned an FL away from the objectives back focal plane, then a double to focus the resulting culminated light to a focus point, then a mask at that point, then another doublet to turn it back to culminated light for the tube lens.

Does that seem right? There was one Olympus that did have phase contrast not in the objective, but a in the path to the camera. I don't remember the model. I think it was one of the inverted ones. Maybe even a 160mm objective (non-infinity) one. But I don't remember.

Thanks,
Ted

abednego1995
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Re: Interference Plane

#2 Post by abednego1995 » Tue May 26, 2020 10:45 pm

One needs to know where the conjugate planes reside.
In your case assuming Koehler illumination is set up, conjugate planes would be like this; light source>condenser iris (condenser side prism interference plane)> objective exit pupil (objective back focal plane, objective side prism interference plane)> exit pupil of the eyepiece (i.e. Ramsden disk)

So... in this train you have to access one of the above planes which is behind or at the objective BFP. As you point out, most high NA objectives have their BFP inside the objective themselves (that's why they use a Nomarski prism rather than a Wollaston to displace the interference fringe outside the prism) so obviously the most accessible plane would be the exit pupil of the eyepiece. Placing irises, phase plates, modulators, and prisms here would be equal to placement in the objective BFP. (Note that since the BFP is "translocated" outside of the objective here, there isn't a need for a Nomarski prism for interference.)

Once the optical transform has been done, we have to reimage it. Placing another eyepiece reverse to the first will make a secondary image plane at its focal point. A image sensor there, or further using a projection lens would enable image output.

I just made an analogy using the eyepieces, but in setups where we need to do this kind of work we use a 4f relay system (please do the googling) It gets complicated, so only select high-end microscopes had this feature incorporated. The most famous would be the Interphako I would reckon.

Cheers,
John

PeteM
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Re: Interference Plane

#3 Post by PeteM » Tue May 26, 2020 11:11 pm

FWIW, Leica's newer infinity objectives are marked A,B,C,D,E etc. for various DIC prisms. And, they publish a chart showing where the internal focal planes are set for each of these (A,B,C,D,E . . .) objectives. Some quite deep into the objective. Probably not a whole lot of help, other than matching prisms, though.

Sure is nice having John participate here -- wish I had a fraction of his optical knowledge.

microb
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Re: Interference Plane

#4 Post by microb » Tue May 26, 2020 11:56 pm

Thanks John and Pete.

This article mentions a modified 4F relay lens in Figure 1C. So I'll take a look again at it: http://www.zia-lab.com/sites/default/fi ... A_2015.pdf

I guess I don't understand the implementation used for the Olympus U-CPA Bertrand lens, which is placed between the objective and tube lens. This patent has a diagram as Figure 1: (https://patents.google.com/patent/US3572885A/en?).

Since the U-CPA unit goes in front of the tube lens, are there lenses not in the patent Figure 1? (http://earth2geologists.net/Microscopes ... ochure.pdf)

I had thought Figure 1a of the Kurvits paper was the same as the U-CPA, but I missed that the Bertrand lens is after the tube lens unlike the U-CPA unit.

abednego1995
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Re: Interference Plane

#5 Post by abednego1995 » Wed May 27, 2020 1:25 am

Yup, the paper from the Zia lab (Fig.1c) illustrates how a 4f-relay is implemented.
Fig.1a has a Bertrand lens behind the tube lens, in this case consider the objective+tube lens as a unit functioning as a finite objective.
Looking at it in that light will fit in with the 1966 patent by Leitz you showed.

The U-CPA Bertrand for the BX series is sort of a nested objective configuration in a infinity setup.
Imagine a low power infinity objective within the attachment. With the tube lens it images the BFP of the other objective to be studied.

These Bertrand lens systems will enable the user to "image" the BFP of the objective, but that "image" is the image of the BFP not the Fourier plane the BFP is.
The BFP is a Fourier plane where the image of the subject is broken down to its Fourier components. So when you insert things in there, you're doing analog spatial filtering, Fourier transforms there.
So... in other words, a microscope isn't just a instrument to magnify objects. It's an analog computer that operates Fourier transforms on optical images.

Cheers,
John

abednego1995
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Re: Interference Plane

#6 Post by abednego1995 » Wed May 27, 2020 1:29 am

>Pete
All manufacturers should publish that BFP location data! Olympus does and as you mention Leitz does... but Nikon doesn't disclose that data (at least on the www.)

microb
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Re: Interference Plane

#7 Post by microb » Wed May 27, 2020 2:13 am

Sorry. I gave the wrong patent. This has a Bertrand lens between the objective and the tube lens, and I'd like to understand how to implement that in a infinity system, which is what the Olympus U-CPA is doing as shown in the patent drawing attached here.

Thanks,
Ted
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microb
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Re: Interference Plane

#8 Post by microb » Wed May 27, 2020 2:32 am

"The U-CPA Bertrand for the BX series is sort of a nested objective configuration in a infinity setup.
Imagine a low power infinity objective within the attachment. With the tube lens it images the BFP of the other objective to be studied."

So if that U-CPA Bertrand lens were replaced with a pair of convex lenses f1+f2 apart and the one closet to the objective f1 from BFP, would that focal point in the center of the 4F be a valid Fourier plane to put a contrast mask at? Also would a third lens, f2+f3 away from the second and inbetween the second and tube lens, be needed to provide the tube lens with culminated light?
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abednego1995
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Re: Interference Plane

#9 Post by abednego1995 » Wed May 27, 2020 3:16 am

Yes, that 1987 patent would be a valid description of how the U-CPA works.

And that 4f relay in the Bertrand position will kind of work...
At least the Fourier plane wouldn't be at the center of L1 and L2. If the focal plane f1 to the left of L1 conincides with the objective BFP, the BFP will be reimaged at the right of L2, at f2.
And no, no need for L3 in an infinity setup.

I'm curious, why use the U-CPA unit? You only have to plop the 4f unit above whatever trinocular you have.
Plus you have to move L1 around to focus on the BFP, whereas using the normal primary image plane through a trinocular lets you have a solid setup with no fiddling about.

microb
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Re: Interference Plane

#10 Post by microb » Wed May 27, 2020 3:24 am

The image of the BFP would be f2 right of l2.

But the Fourier plane would be f1 right of l1, f2 left of l2. Right?

Thanks,
Ted

abednego1995
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Re: Interference Plane

#11 Post by abednego1995 » Wed May 27, 2020 3:26 am

The BFP is the Fourier plane of the objective :-)
So if the BFP is at the left of L1, it will be relayed to the right of L2.
The 4f relay is normally used to Fourier transform the "image" made by the objective by L1, and do a following inverse Fourier transform with L2.

If you're relaying the BFP with a 4f relay, you'll get the "image" made by the objective at the middle of the relay (yes, L1 is doing an inverse Fourier transform here) and L2 will do a Fourier transform to get BFP' on the right side of it.

abednego1995
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Re: Interference Plane

#12 Post by abednego1995 » Wed May 27, 2020 3:41 am

BTW, Nikon does it like this in their "External Phase Contrast" system on their inverted microscopes.
IMG_1642.jpg
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microb
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Re: Interference Plane

#13 Post by microb » Wed May 27, 2020 5:17 am

"I'm curious, why use the U-CPA unit? You only have to plop the 4f unit above whatever trinocular you have.
Plus you have to move L1 around to focus on the BFP, whereas using the normal primary image plane through a trinocular lets you have a solid setup with no fiddling about."

I'm just trying to understand the plumbing here.

So the U-CPA would be one lens for Bertrand functionality, and that's what Olympus was selling. As for putting a phase contrast mask in there, ok, the option is possible at the eyepiece/trinocular camera port.

In trying to picture the other conjunctive planes, using the example of a spinning confocal disk -- basically pin hole cameras placed between the objective and the tube lens. Would that system need to have a lens in-between the disk and the tube lens to culminate the light like the green lens shown previously?

Thanks.

microb
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Re: Interference Plane

#14 Post by microb » Wed May 27, 2020 5:19 am

abednego1995 wrote:
Wed May 27, 2020 3:26 am
The BFP is the Fourier plane of the objective :-)
So if the BFP is at the left of L1, it will be relayed to the right of L2.
The 4f relay is normally used to Fourier transform the "image" made by the objective by L1, and do a following inverse Fourier transform with L2.

If you're relaying the BFP with a 4f relay, you'll get the "image" made by the objective at the middle of the relay (yes, L1 is doing an inverse Fourier transform here) and L2 will do a Fourier transform to get BFP' on the right side of it.
Ok. I can see that. Thanks.

microb
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Re: Interference Plane

#15 Post by microb » Wed May 27, 2020 5:37 am

abednego1995 wrote:
Wed May 27, 2020 3:41 am
BTW, Nikon does it like this in their "External Phase Contrast" system on their inverted microscopes.

IMG_1642.jpg
So for the Nikon assembly, would a series of two Steinheil triplet achromatic lenses near the objective side, plus a Hastings to feed into the tube lens side be a good optimal set up?

(https://www.thorlabs.com/newgrouppage9. ... up_id=5368)
(https://www.thorlabs.com/newgrouppage9. ... up_id=5370)

abednego1995
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Re: Interference Plane

#16 Post by abednego1995 » Wed May 27, 2020 6:47 am

Well... in a infinite system with a spinning disk confocal setup you should have the pinhole disk "after" the tube lens (or secondary objective, in Nikon jargon)
That pinhole at the primary image plane eliminates light from the other defocused planes and at the same time acts as the illuminating aperture.
A relay lens system then images the pinhole on to a planar sensor. Most spinning disk confocal schematics I've seen skip a lot of elements, so see Fig.1 in the linked paper.

https://www.osapublishing.org/DirectPDF ... &mobile=no

Not sure where you got the information for those lenses from Thorlabs, but the Zia lab paper you linked has Thorlabs product numbers for their setup which "should" work.

microb
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Re: Interference Plane

#17 Post by microb » Wed May 27, 2020 3:01 pm

abednego1995 wrote:
Wed May 27, 2020 6:47 am
Well... in a infinite system with a spinning disk confocal setup you should have the pinhole disk "after" the tube lens (or secondary objective, in Nikon jargon)
That's why I'm asking, because Thorlabs does it above the tube lens, which I can follow the design of. https://www.thorlabs.com/newgrouppage9. ... ad-image-0

But Olympus has the U-CFU Confocal Unit and Technical Instruments had their K2 unit which are both placed in the infinity track as epi replacements. So I'm trying to figure out how the pinhole works in that case.

apochronaut
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Re: Interference Plane

#18 Post by apochronaut » Wed May 27, 2020 3:54 pm

microb wrote:
Tue May 26, 2020 8:54 pm
Can one put a Bertrand-like lens between camera and objective, have it aimed at the interference plane, then at the lens's other side at a focal distance away put Hoffman or phase contrast masks? Another lens would then switch it back to infinity focus.
Thanks,
Ted
To go back to your original question. Did Fritz Zernike not basically do that with his prototype phase system? Contrary to the misconception that his prototype involved the condenser and or objectives, in a similar arrangement to many modern systems, it was nothing of the sort. Zernike's phase plates were located at the conjugate plane of the eyepiece , recombining the waves which were subsequently relayed to an eyepiece further up the optical tube. Everything took place above the eyepiece exit pupil. Presumably there were symmetrical relay lens systems in his rig, not above the objective as in your example question but in a location where he could add a convenient complete accessory to an existing microscope stand.

The adaption of phase to the diaphragm and objective conjugate planes was a further development by several microscope companies, at which point they engineered purpose built stands and objectives, which showed promise as superior designs to Zernike's DIY prototype .

microb
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Re: Interference Plane

#19 Post by microb » Wed May 27, 2020 5:05 pm

I'm liking the idea of augmenting at the eyepiece image plane. I could add Hoffman modulating contrast to a Leica DMIL 160mm objective microscope by extending the neck below the trinocular. I guess one could even add a small epi there.

abednego1995
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Re: Interference Plane

#20 Post by abednego1995 » Wed May 27, 2020 11:19 pm

Erm, wouldn't Thorlabs confocal system be a laser scanning confocal?? That's different from a spinning disk confocal.

Ah! Do you have a DM IL??
That slider slot under the head accepting the Hoffman sliders is actually conjugate with the objective BFP...

Cheers,
John

microb
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Re: Interference Plane

#21 Post by microb » Thu May 28, 2020 12:13 am

abednego1995 wrote:
Wed May 27, 2020 11:19 pm
Erm, wouldn't Thorlabs confocal system be a laser scanning confocal?? That's different from a spinning disk confocal.
Yes it is scanning, but it has a pin hole -- just a single one instead of a spinning disk's array of them. So I'm using the Thorlabs scanning set-up as an example of a pin hole camera above the tube lens, which I can understand.

The spinning disk units that are below the tube lens and replace the epi must have a lens to convert the infinite to a focal point, put the disk there, and then convert back to infinite.

hans
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Re: Interference Plane

#22 Post by hans » Sat Aug 08, 2020 8:14 pm

microb wrote:
Tue May 26, 2020 8:54 pm
Can one put a Bertrand-like lens between camera and objective, have it aimed at the interference plane, then at the lens's other side at a focal distance away put Hoffman or phase contrast masks? Another lens would then switch it back to infinity focus.
abednego1995 wrote:
Tue May 26, 2020 10:45 pm
I just made an analogy using the eyepieces, but in setups where we need to do this kind of work we use a 4f relay system (please do the googling) It gets complicated, so only select high-end microscopes had this feature incorporated. The most famous would be the Interphako I would reckon.
It sounds like something along these lines was an option on the Reichert UnivaR? (I was just looking at the manual since John mentioned it to me as an example of having zoom optics in the illumination path.) From William Porter's translation posted in this thread which now appears to be hosted here:
The relay system is an apochromatic transport optical path that can be inserted between objectives and eyepiece. It generates intermediate pictures of the image field and the objective pupil. In this path are then made the necessary interventions in the optical path of the microscope, while lenses and eyepieces remain unchanged. In the image plane, different field insertions can and will be accommodated in the objective pupil phase rings for phase and anoptral contrast.

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