Magnification of the NFK eyepiece in the Olympus BH-2 system

[onilink_]

Hello!

So a friend of mine sold me a NFK 3.3x and a U-PMTVC in very good condition for a very good price.

I use daily an Olympus BH2 with the epi-illumination system for light reflected microscopy with a Swiftcam SC300 microscope camera (1/2" sensor) and it's 0.5x lens adapter directly plugged in the trinocular head of my microscope.
Obviously the problem with that setup is a don't have the corrections required to match the MSPlan objectives I use.

With the NFK and C-mount adapter, the image is actually way better, but the magnification is really strong. Much stronger than with the 0.5x adapter.

I imagine that the question has already been asked somewhere and that there is no conclusive solution, given the price of the NFK 1.67x ... but is there a way to fix this?
And if not why is this the case?

If I understand well the corrections are made by the eyepiece or the NFK. If so is it possible to use a different C-mount adapter with an higher reduction than mine?

Also my microscope have a magnification wheel with 1.0x, 1.25x and 1.50x.
Maybe a stupid question but, Isn't there a way to replace it with a lens that zooms out instead?

In any case I'm very interested in how this microscope works. So any answer or general information is welcome.

Thank you for your time, and have a good day.

[apochronaut]

I m not 100% sure of the question but it seems to be why there is no easy way to get adequate corrections for your Olympus to 1/2" sensor system coupled with
adequate frame reduction ?
Photo eyepieces such as the NFK 3.3X were originally used with a film camera that had a frame size considerably larger than your 1/2" sensor., thus greater magnification was required of the eyepiece. However, there should be some optic available for cctv or 16mm emulsion film that matches the NFK corrections. Might take some experimenting, though. I remember from photo optic tests I did a few years ago that the NFK eyepieces had quite unique corrections compared to the other photo eyepieces I tested, which were only marginally different. There was also a specific tube length required : 125mm I think.
If I am not mistaken, the NFK may be compensating types but I would have to check to be sure.

[PeteM]

Film was the dominant medium at the time your BH2 was built, so the photo relay lens choices are oriented toward film (35mm, Polaroid, etc.) or small sensor video. At that time, the objectives also had eyepiece corrections.

I assume your MSPlan objectives are the "f=180" type and not some earlier Olympus offering. If so, they were designed to use the regular BH2 heads and eyepiece corrections.

A 2.5x NFK relay lens would help a little bit on sizing. Another option would be to shoot "afocal" through a regular eyepiece and a camera perched above the 10x eyepiece and using a camera lens with as little distortion as possible. The Web will be your friend in learning more about this.

Your 1/2" microscope camera is one limitation. The .5x adapters commonly made are also of mediocre quality. You might consider looking for a used mirrorless or DSLR body, with live viewing and an electronic shutter, and using a 2.5x Olympus NFK photo relay lens.

[Scarodactyl]

From what I understand micro 4/3 pairs well with the 3.3x/mtv3 combo (giving net 1.1ishx magnification).

[onilink_]

I m not 100% sure of the question but it seems to be why there is no easy way to get adequate corrections for your Olympus to 1/2" sensor system coupled with
adequate frame reduction ?
Photo eyepieces such as the NFK 3.3X were originally used with a film camera that had a frame size considerably larger than your 1/2" sensor., thus greater magnification was required of the eyepiece. However, there should be some optic available for cctv or 16mm emulsion film that matches the NFK corrections. Might take some experimenting, though. I remember from photo optic tests I did a few years ago that the NFK eyepieces had quite unique corrections compared to the other photo eyepieces I tested, which were only marginally different. There was also a specific tube length required : 130mm I think.
If I am not mistaken, the NFK may be compensating types but I would have to check to be sure.

Hello,
To make it short I'm looking for a way to reduce the high magnification for my small sensor, if possible.
So I want to understand how it works. Or if anyone has a ready solution I'm also interested

What do you mean by "may be compensating types" ?
Something to do with chromatic aberration?

Film was the dominant medium at the time your BH2 was built, so the photo relay lens choices are oriented toward film (35mm, Polaroid, etc.) or small sensor video. At that time, the objectives also had eyepiece corrections.

I assume your MSPlan objectives are the "f=180" type and not some earlier Olympus offering. If so, they were designed to use the regular BH2 heads and eyepiece corrections.

A 2.5x NFK relay lens would help a little bit on sizing.

Yes indeed, infinity corrected objectives with f = 180.
For the 2.5x NFK yes you are right but I would still have a strong zoom. For what I calculated it will be comparable to using the 1.5x magnification of the wheel with my current setup (so with the swiftcam 0.5x reduction lens).

Another option would be to shoot "afocal" through a regular eyepiece and a camera perched above the 10x eyepiece and using a camera lens with as little distortion as possible. The Web will be your friend in learning more about this.

Oh so this is possible?

Your 1/2" microscope camera is one limitation. The .5x adapters commonly made are also of mediocre quality. You might consider looking for a used mirrorless or DSLR body, with live viewing and an electronic shutter, and using a 2.5x Olympus NFK photo relay lens.

Yeah I have a friend who bought a Sony mirrorless body and the image quality is very impressive. He also uses a 2.5x NFK.

I still have to try the 0.5x adapter on another microscope (that don't requires specific corrections) to see if it's really that bad. I haven't really had the chance to compare, but you're not the first to tell me it's poor quality.

From what I understand micro 4/3 pairs well with the 3.3x/mtv3 combo (giving net 1.1ishx magnification).

Yes the problem is really my sensor, it's very small.

Thank you everyone for the answers!

[apochronaut]

Compensation is a way of evening out the various aberrations in an optical system by first overcorrecting in one component and then undercorrecting in another downstream component. The undercorrecting component is called a compensating lens and more often than not is usually a compensating eyepiece.
In the past, prior to the invention of many of the glass types used in microscope systems today compensation was required in order to install adequate corrections into the final image and seldom do a manufacturer's compensations match another's.
Using a compensating eyepiece where less compensation or further correction is required will result in peripheral ca with reversed colours.
NFK eyepieces are compensating , so in order to find another mfg's. low magnification eyepiece that will give you properly corrected photos, the other eyepiece would have to have equivalent levels of compensation as well as have the required low magnification.
I still wonder what Olympus did for 16mm emulsion film or cctv. Certainly there was a fractional magnification optic for thos applications? There must have been some microscopes using the LB objectives also so fitted for small frame format systems. In a similar vein, the AO series 420, which was more or less contemporary to the BH series had a special video cam adapter, with a dovetail that fitted under the head, extending to the rear of the arm where a video relay lens was located plus a c mount. Olympus must have had something similar.

[onilink_]

Compensation is a way of evening out the various aberrations in an optical system by first overcorrecting in one component and then undercorrecting in another downstream component. The undercorrecting component is called a compensating lens and more often than not is usually a compensating eyepiece.
In the past, prior to the invention of many of the glass types used in microscope systems today compensation was required in order to install adequate corrections into the final image and seldom do a manufacturer's compensations match another's.

Ooh ok thank you for the explanation.
Does it also work like that for apochromatic objectives?

Using a compensating eyepiece where less compensation or further correction is required will result in peripheral ca with reversed colours.
NFK eyepieces are compensating , so in order to find another mfg's. low magnification eyepiece that will give you properly corrected photos, the other eyepiece would have to have equivalent levels of compensation as well as have the required low magnification.

I see. But how do it works after the eyepiece? Can you use a C-mount adapter from another microscope / vendor? Or do you have to use the U-PMTVC especially for the NFK?
Does the lens inside also need to do some corrections?

Also, does the distance of the sensor relative to the C-mount lens is important for corrections?
What happens if I add a spacer between the C-mount and the camera for example?

[Tom Jones]

The U-PMTVC is actually for the BX series, but does a nice stand-in for the BH-2 Series MTV-3. The U-PMTVC has an adjustment for parfocality and the MTV-3 does not. The both have the 0.3x reduction lens as they were designed for C-mount cameras.

I use the U-PMTVC and a 3.3x NFK projection lens for my Panasonic GH4 to shoot 4K video. I get the eyepiece corrections from the NFK, and the frame size reduction back to essentially direct projection (3.3x x 0.3x = 0.99x). Even that's only good, not perfect. And as I recall, not all that good for stills. That setup won't come close to working for my Canon R5 full frame camera. That get a 2.5x (PE or NFK depending on the system) and no other optics prior to the film plane. That camera has a massive number of different frame dimensions depending on how you shoot.

One of the enduring issues with microscopes, cameras and camera mounts is that unless you are using a film or sensor size matching film formats (full frame 35mm, etc.) it is unlikely you will find a perfect solution using a manufacturers adapters. Even then, perfect is debatable. There are just too many different sensor sizes and formats. Even the same camera will likely use a different sensor area for different frame rates for video, and different yet for stills. That's just the price of admission. Even other manufacturers generic adapters suffer from the same differences in the part of the sensor actually used. You are going to lose something in the image circle due to the frame dimension crop of the adapters, or you are going to lose camera sensor pixels with the round image circle shooting afocally. Pick one close enough and go for it. It will save on psychotherapy costs!

Here is Alan Wood's page on attaching a C-mount camera to a BH-2:

https://www.alanwood.net/olympus/c-moun ... scope.html

Here's something from Charlie Krebs site that might provide a little more background:
https://krebsmicro.com/photomic1/photomic1.html and https://krebsmicro.com/relayDSLR/relayoptics1.html

[imkap]

Hi everyone, I hope you're doing well.

It is cheaper to buy a used full frame camera than nfk 1.67. I have a Sony and it serves me well.

[apochronaut]

Compensation is a way of evening out the various aberrations in an optical system by first overcorrecting in one component and then undercorrecting in another downstream component. The undercorrecting component is called a compensating lens and more often than not is usually a compensating eyepiece.
In the past, prior to the invention of many of the glass types used in microscope systems today compensation was required in order to install adequate corrections into the final image and seldom do a manufacturer's compensations match another's.

Ooh ok thank you for the explanation.
Does it also work like that for apochromatic objectives?

Using a compensating eyepiece where less compensation or further correction is required will result in peripheral ca with reversed colours.
NFK eyepieces are compensating , so in order to find another mfg's. low magnification eyepiece that will give you properly corrected photos, the other eyepiece would have to have equivalent levels of compensation as well as have the required low magnification.

I see. But how do it works after the eyepiece? Can you use a C-mount adapter from another microscope / vendor? Or do you have to use the U-PMTVC especially for the NFK?
Does the lens inside also need to do some corrections?

Also, does the distance of the sensor relative to the C-mount lens is important for corrections?
What happens if I add a spacer between the C-mount and the camera for example?

Originally compensating eyepieces were commonly used with apochromats since correction for spherical aberration resulted in over correction for ca. In the early 60's, manufacturers had access to newer low dispersion glass types and one of two practices resulted. 1) All objectives were over corrected equally allowing for the use of the same compensating eyepiece for both achromats and apochromats 2) All objectives were corrected close to or ideally and completely , allowing for the use of the same mildly correcting or neutrally correcting eyepiece with both achromats and apochromats.
Olympus used the former system up until at least the LB objective series.

The distance from the eyepiece to the sensor can be a problem with certain photo eyepieces, probably those that are more highly corrective or compensating. Some neutral eyepieces seem pretty oblivious to that distance, affecting the objective working distance more than anything. Olympus might fall into the category of being projection distance sensitive, since they stipulate a distance of 125mm from the eyepiece to sensor.

[onilink_]

I use the U-PMTVC and a 3.3x NFK projection lens for my Panasonic GH4 to shoot 4K video. I get the eyepiece corrections from the NFK, and the frame size reduction back to essentially direct projection (3.3x x 0.3x = 0.99x). Even that's only good, not perfect. And as I recall, not all that good for stills.

Not all that good for what reason? You have some chromatic aberration?

One of the enduring issues with microscopes, cameras and camera mounts is that unless you are using a film or sensor size matching film formats (full frame 35mm, etc.) it is unlikely you will find a perfect solution using a manufacturers adapters. Even then, perfect is debatable. There are just too many different sensor sizes and formats. Even the same camera will likely use a different sensor area for different frame rates for video, and different yet for stills. That's just the price of admission. Even other manufacturers generic adapters suffer from the same differences in the part of the sensor actually used. You are going to lose something in the image circle due to the frame dimension crop of the adapters, or you are going to lose camera sensor pixels with the round image circle shooting afocally. Pick one close enough and go for it. It will save on psychotherapy costs!

Tbh I don't care at all about afocality / parfocality (If I understand well what you mean).
My main problems are chromatic aberration and depth of field. I'm very far from seeing the round image because cropping is like 80%...

What I don't understand is if I can use something else than my C-mount adapter (or after it) and not lose corrections of the NFK eyepiece.
I mean, what does the U-PMTVC exactly? It is just a reduction lens?

Hi everyone, I hope you're doing well.

It is cheaper to buy a used full frame camera than nfk 1.67. I have a Sony and it serves me well.

Hi, and yeah, that's what I read everywhere... I know someone with a full frame Sony and indeed results are pretty good.

Originally compensating eyepieces were commonly used with apochromats since correction for spherical aberration resulted in over correction for ca. In the early 60's, manufacturers had access to newer low dispersion glass types and one of two practices resulted. 1) All objectives were over corrected equally allowing for the use of the same compensating eyepiece for both achromats and apochromats 2) All objectives were corrected close to or ideally and completely , allowing for the use of the same mildly correcting or neutrally correcting eyepiece with both achromats and apochromats.
Olympus used the former system up until at least the LB objective series.

The distance from the eyepiece to the sensor can be a problem with certain photo eyepieces, probably those that are more highly corrective or compensating. Some neutral eyepieces seem pretty oblivious to that distance, affecting the objective working distance more than anything. Olympus might fall into the category of being projection distance sensitive, since they stipulate a distance of 125mm from the eyepiece to sensor.

Interesting... Thank you for this addition.

So if I understand well, corrections are only made on the eyepiece (if not neutrally correcting) to match the objective right? Not on the the U-PMTVC? I suppose this one is made in such a way to project the image at the correct distance on the sensor?

[Tom Jones]

My main problems are chromatic aberration and depth of field. I'm very far from seeing the round image because cropping is like 80%...

If you want a round image, you will need to shoot through the eyepiece afocally. That's what it's called when you shoot through the eyepiece like you look through it as you would with a cell phone. Parfocality is having the eyepiece and camera views in focus together at the same place. When you look in the eyepieces and a part of the specimen is in focus, then look on the screen at the camera view, that part of the specimen will have the same areas in focus. It's really nice to have, but not necessary with digital systems where you can focus via the screen.

Depth of field is controlled by the objective. All optical elements that come after it are only magnifying and maybe modifying the image produced by the objective. Depth of field is not a problem. For any given objective it just is what it is, and the higher the magnification the shallower it generally is. The eyepiece/projection lens (Olympus BH-2) also add the final color corrections to that image. That's not true with the newer BX infinity series of objectives and projection eyepieces where all corrections are done in the objective.

Did you read the Krebs links I gave you? He does a really nice job of explaining the issues of camera sensor and frame sizes vs projection lenses. He's a professional photographer who has won more Nikon Small World and Olympus photomicrography competitions than pretty much anyone. He knows his stuff.

[onilink_]

If you want a round image, you will need to shoot through the eyepiece afocally. That's what it's called when you shoot through the eyepiece like you look through it as you would with a cell phone. Parfocality is having the eyepiece and camera views in focus together at the same place. When you look in the eyepieces and a part of the specimen is in focus, then look on the screen at the camera view, that part of the specimen will have the same areas in focus. It's really nice to have, but not necessary with digital systems where you can focus via the screen.

Depth of field is controlled by the objective. All optical elements that come after it are only magnifying and maybe modifying the image produced by the objective. Depth of field is not a problem. For any given objective it just is what it is, and the higher the magnification the shallower it generally is. The eyepiece/projection lens (Olympus BH-2) also add the final color corrections to that image. That's not true with the newer BX infinity series of objectives and projection eyepieces where all corrections are done in the objective.

Did you read the Krebs links I gave you? He does a really nice job of explaining the issues of camera sensor and frame sizes vs projection lenses. He's a professional photographer who has won more Nikon Small World and Olympus photomicrography competitions than pretty much anyone. He knows his stuff.

Thank you for the answer.
Sorry, I didn't mean depth of field but field of view. I got confused.

I don't want particularly a round image, but I don't want to lose 80% of the field of view
My main concern about shooting through the eyepiece afocally is my reduction lens (I think), supplied with the camera, and it seems to be the main source of chromatic aberrations.
Because if I understand correctly, I'll need a lens to project the image coming out of the eyepiece onto the sensor of my camera (because it's a virtual image, right?).

I'll try to 3d print a support and make some experiments.

Also, I have a Canon EOS 100D. Maybe it's worth a try with the NFK and the U-PMTVC? I suppose I just need a C-Mount adapter?

And yes, I read the Krebs article. But it's really not simple to understand in one single reading (now even three).
It also seems that some of the rules he mentions don't work with this microscope... Like the fact that corrections on the objectives are generally only for non infinity corrected microscopes?

In microscopes that use an infinity-corrected optical system, these final corrections, if needed, are made by the internal tube lens. Thus, the intermediate image can be considered “finished” for all practical purposes. No addition correction need be made to improve the image quality.

[deBult]

Your BH2 does NOT have an infinity corrected optical system, it is finite so a NFK correction eyepiece IS required.

“Because if I understand correctly, I'll need a lens to project the image coming out of the eyepiece onto the sensor of my camera (because it's a virtual image, right?).”

Using the L-tube or the U-PMTVC and the NFK projection lens you do NOT require a camera lens to project the image out of the eyepiece onto the sensor.

Using a normal eyepiece you DO need this camera lens.

May I suggest (re-)reading the Alan Wood website on camera connection to the BH2.

[onilink_]

Your BH2 does NOT have an infinity corrected optical system, it is finite so a NFK correction eyepiece IS required.

I have the epi-head and the objectives are infinity corrected, so my BH-2 is a strange beast
But yeah I know I need the NFK. That's why I bought it.

Using the L-tube or the U-PMTVC and the NFK projection lens you do NOT require a camera lens to project the image out of the eyepiece onto the sensor.

Using a normal eyepiece you DO need this camera lens.

Yes I was talking about using the eyepiece afocally and not the NKF.

Any idea if I can replace the shitty lens of my microscope camera (SCA-EA05) with some old Canon Coolpix objective ?
I have one that died and the lenses seem to be good quality.
Has anyone ever tried this type of DIY?

[carlh6902]

Since the LB objectives used on the BH2 are not fully compensated, they rely on the eyepieces and NFK protection optics to complete the compensation of the intermediate image produced by the objectives. You therefore MUST use an NFK in the trinocular port.

Carl