Question about Zeiss Correcting Oculars

[cmtalb01]

I would like to ask for help answering a question about correcting eyepieces. I have several sets of Zeiss and Nikon eyepieces (see photo), and an Olympus Photo eyepiece and would like to see if someone could direct me to documentation explaining the difference between the KPL and CFL specifically (if any - may just be a translation difference??). Also, if anyone could point information about the Nikon CFW corrections and the Olympus FK corrections I would be appreciative.

I use the Olympus in the photo tube of the Zeiss PM, and the Nikon set is my go to choice for binoc oculars. I had the older 12.5X from an old Pol scope, and recently purchased the Zeiss Kpl and CPL sets, However up until this weekend I refrained from using them because they did not have rubber eye cups and tended to scratch the AR coating of my glasses. That problem is now solved.

Thanks for your help!

[MicroBob]

The KPL were the best corrected eyepieces. The CPL are "clinical plan" = good enough for eveyday routine use. The "C" type is the simplest. It also compensates for the objectives chromatic error but is not planar and has a small field of view. The CPL introduce a heavy field curvature that is somewhat distracting.

When you take a high contrast slide, e.g. a micrometer slide you can see at the border of the field of view whether the eyepieces match the objectives. If a line is accompanied with yellow and blue lines they don't match very well.

[apochronaut]

That's a good test for compatible chromatic corrections.

Eyepieces are best used with the objectives they were intended for unless : one has been able to carefully test compatibility. In order to test compatibility, many factors need to be considered and it helps to have an array of eyepieces to make comparisons with. Achromat systems are never completely corrected, even the best of them, so it is hard to know just how much correction to expect. It is unlikely that an eyepiece made for another microscope will improve on the one made by the instruments mfg. but it does happen, occasionally.
It used to be that most achromats were quite similar in design , so the standard Huygens eyepiece could be tweaked a little to increase colour correction with a given objective but would still work quite well with others. A degree of chroma and curvature were normal and acceptable.

After W.W. II companies went crazy, eradicating curvature of field and lateral chroma in the objectives via innumerable technical solutions and always there was a degree of dependency on a compatible eyepiece to participate in the solutions. Thus , most objectives and eyepieces of advanced formula, come in matched pairings, even within the confines of an individual manufacturers engineering preoccupations.

As time wore on , directions were taken to increase the totality of corrections within objectives, depending again on the manufacturers preoccupations. Whole families of proprietary "systems" emerged. Many systems , incorporated the contribution of correcting tube lenses, relieving the eyepiece from the necessary burden of supplying corrections.

Many eyepieces produced since about 1980 are thewrefore non-correcting, being simple accurate magnifiers of a well corrected image.

So, to encapsulate all, that into periods. 1) pre-war huygens, Ramsden and Kellner design eyepieces are usually very simliar to each other and fairly cross compatible.
2) Other eyepiece designs from the pre-war ; Compensating, Kompens, Hyperplane and proprietary designs made between W.W. II and up to about 1980 are pretty specific to proprietary objective designs or optical train designs and are cross compatible with others only by accident.
3) Since approx.1980 there has been more development of completely corrected optical systems, certainly since infinity correction has pretty much ruled the day and eyepieces are more likely cross compatible.

Generally, eyepieces designed for stereo microscopes are not compatible with Diascopic or Epicscopic microscopes, although some odd coincidences do occur.

[photomicro]

It is interesting that you go to the Nikons, as they are the only ones shown that have no corrections at all for chromatic aberration, being designed for use with their 'CF' (chroma free) system of lenses where all the corrections were made in the objective.

All the others are 'compensating' types, and as such designed for the manufacturers own optics. Thus, the Zeiss CPL and KPL for Zeiss, and your Olympus Photo eyepiece for Olympus.

Whilst the eye cannot always detect such nuances in use, you can certainly see the effects when taking photographs. Your FL 2.5 x is useful in being low magnification, and forms a real image, as it is a photo eyepiece, it was designed for the short barrel Olympus objectives such as the BH and CH. As such, it isn't really ideal for your Zeiss objectives.

Having said that, you haven't actually said what objectives you use.

[Hobbyst46]

The various photo eyepieces from Olympus, like FK and NFK, were described in detail by Alan Wood in one of the microscopy sites.

[cmtalb01]

Thank you all for the replies, exactly what I was needing to know. After posting, I reviewed a copy of Zeiss Optical Systems, and found in section 72 the following: "C-type eyepieces may be used in conjunction with simple types of objective. Objectives of higher correction should, if possible, always be combined with Kpl eyepieces. This applies above all to the Plan-achromats and Planapochromats."

So given this and the great information that you all provided, I had some very interesting results.

First to answer some questions. I used the Nikon because they have a very comfortable eye-relief and came with my first Zeiss Pol scope. Until recently, they were the best eye pieces that I had. And only until this weekend the only ones with rubber eye cups (very important to me to protect the AR coating of my glasses).

As far as objectives go, aside from a Hoffman modulation 40X, and a McCrone dispersion objective the rest are all Zeiss brand, and include a couple sets of Epiplan HD (4 to 80X), a couple sets of EpiPlan Pol (4 to 80X), a set of planchromats (phase 10 to 100X), a set of neofluar (10 to 100X), a 100X Planapochromat, one 2.5X apochromat, a 100X planachromat, and a Zeiss 100X "F" series.

So took a Zeiss micrometer slide and the 40X HD, EpiPlan Pol, phase, Hoffman, and neofluar, and examined with all three eyepieces (Nikon, Cpl and Kpl for yellow lines on the edge of the field of view as suggested (Thanks!!) And just as described I saw the yellow band along side the micrometer marking on the outer edge of the field of view with the Nikon on all objectives except the HD (it was there but very diffuse and faint). The Cpl eyepiece removed this yellow band significantly for all Zeiss objectives but there still remained a very diffuse but faint yellow "area" running along side the micrometer ruling. The neofluar objective and the Cpl eyepiece was actually the best of this set - as might be expected. Finally, with the Kpl eyepieces, and for all Zeiss objectives this yellow band was not present. The "sharpest" or "whitest" or "cleanest" view appeared to be with the Kpl eyepiece and neofluar objective (as expected).

I need to print some sort of adapter for my photo camera to attach to the eyepiece but I will try and take some pictures of this through the eyepieces and post what I get.

Thanks everyone for your comments - extremely helpful!!

[MichaelG.]

Thank you all for the replies, exactly what I was needing to know. After posting, I reviewed a copy of Zeiss Optical Systems, and found in section 72 the following: "C-type eyepieces may be used in conjunction with simple types of objective. Objectives of higher correction should, if possible, always be combined with Kpl eyepieces. This applies above all to the Plan-achromats and Planapochromats."

So given this and the great information that you all provided, I had some very interesting results.

[ ... ]

Finally, with the Kpl eyepieces, and for all Zeiss objectives this yellow band was not present. The "sharpest" or "whitest" or "cleanest" view appeared to be with the Kpl eyepiece and neofluar objective (as expected).

I need to print some sort of adapter for my photo camera to attach to the eyepiece but I will try and take some pictures of this through the eyepieces and post what I get.

Thanks everyone for your comments - extremely helpful!!

Thank you for posting the result of your practical test.
It is becoming increasingly useful to have the characteristics of 'finite tube' optics documented.
... I look forward to seeing the pictures.

MichaelG.
.
Edit: If you could include the Olympus FK 2.5x in your photographic testing; that would make an interesting comparison and be much appreciated. ... It is, of course, designed for direct imaging by projection; whereas you will presumably be using a camera lens with the others.

[MicroBob]

Newer eyepieces often offer a more comfortable view compared to older ones. So you might end up using an eypiece that doesn't fit perfectly from the chromatic correction but offers the most agreeable view nontheless. It's good to know and apply the theory and then just use what is good in practice.
For compensating eyepieces Zeis West and Zeiss Jena are similar, Leitz is a bit away but acceptable, and Olympus is further away and so closer to Leitz.
For best results the point where the eyepiece expects the image is also important.

[cmtalb01]

Thanks to everyone again who replied. I used the information given and ran tests on all the 40X objectives and eyepieces that I had available. Summary results first and then details to follow.

Obviously, the best combination was the Zeiss KPL and Neofluar objective, followed by the Zeiss CPL and same Neofluar objective.

Also, I apologize for the dirt, the dry weather of late makes it almost impossible to keep dust from clinging to the glass even immediately after cleaning

Eyepieces: Nikon CF W 10X, Olympus FK2.5X photo, Zeiss KPL 10X, Zeiss CPL W 10X, and Zeiss KPL W 10X
Objectives (all 40X): Zeiss Epiplan HD, Zeiss Epiplan Pol DIC, Zeiss Planachromat Phase, Zeiss Neofluar, Hoffman Modulation

First a collection of images from the objective/eyepiece combinations.

Nikon CF W
The Nikon CF wide eyepiece is very comfortable to use and has a wide field of view, the CF stands for Chrome Free and is corrected for Nikon Objectives. This eyepiece shows he yellow ghost line aberration in the full field of view for the Zeiss Planacrhomat phase and HD objectives. The aberration is almost non-existent in the HM objective (which may be Nikon) and exhibits as a grey color in the Zeiss DIC objective. The Zeiss Neofluar shows no aberration with this objective.

Olympus FK2.5X
The Olympus FK photo objectives were designed with corrections for the 36.65mm short barrel objectives and is used on my scope as the projection lens on the trinoc head to a Sony alpha 6000 camera using a Canon F microscope adapter. As seen from the tests, aberrations can be seen in the full field of view for the Zeiss Epiplan phase, HD, and Hoffman Mod. Objectives, and slightly on the outer edges of the Neofluar objective. The Zeiss Epiplan DIC objective does not appear to show aberrations with this eyepiece.

Zeiss KPL 10X
An older Zeiss KPL eyepiece demonstrated significant chromatic aberrations with the Zeiss Planachromatic phase and Hoffman Modulation objectives across the full field of view. The HD and DIC objectives also showed aberrations but more towards the edge of the field. The Neofluar showed a very slight aberration and only at the extreme edge of the field of view.

Zeiss CPL W 10X
The Zeiss CPL eyepiece performed very well with no aberrations observed in the objectives with the exception of a very slight yellow line visible in the Zeiss planachromat phase objective.

Zeiss KPL W 10X
As expected the Zeiss KPL W eyepiece also performed very well with all objectives. An extremely slight aberration was seen with the Zeiss Planacrhomat phase objective. In addition, this eyepiece gave the sharpest images of all eyepieces.

[MichaelG.]

A very interesting, and thought-provoking set of results.
... Many thanks for sharing them.

MichaelG.

[Hobbyst46]

I have run through a fairly similar situation.
My viewing eyepieces are Olympus WHK 10x18 or 10x 20. They are excellent and very convenient to use.
My objectives are 6.3x, 16x, 40x Zeiss Plan achro, 40x Planapo, 40x neofluar phase, 63 and 100 Planap phase.
And a single Olympus SPlan 10x0.30. They are all more or less parfocal with each other.

For photo eyepieces I tried an old Zeiss 10x KPL, Nikon 10x, Olympus FK5.0. And a partially delaminated Zeiss 10x W
KPL. And an Olympus WHK 10x18.
The stage micrometer is a "reverse" type - bright lines on a black opaque background.
My survey was sketchy, however there are two important conclusions. For me at least.
1. Must achieve exact parfocality between the viewing eyepieces and the photoeyepiece. Perfect parfocality was obtained only with the Zeiss 10x photoeyepieces. The others had to be "pushed downwords", which is impossible, since the phototube is fixed.
2. Using the Zeiss photoeyepieces, chromatic aberrations were most evident with the Planachromats - the 6.3x, 10x, 16x
yielded violet micrometer lines - and much less with the neofluar and Planapos, that yielded white micrometer lines, although on the periphery of the image yellow and blue dots do show.

I have no 10X Zeiss objective, so unable to compare the Olympus 10x chromatic corrections to Zeiss objectives of the same magnification. But the chromatic aberrations appeared to be similar.

Finally, I found that rubber eyecups of all sizes are for sale on the internet.

[cmtalb01]

Apologies to keep bugging everyone with this, but I wasn't satisfied with my last posting. I knew that my PM was not optimally aligned and I was confident that there were artifacts in the images due to alignment. So, I followed Paul James method of aligning the PM Headrig (Mic-UK) and performed a thorough cleaning at the same time...and repeated the testing. Very pleased with the outcome and also aligned the Universal using the same method.

Summary: Best correction eyepiece and objective combinations are shown with green "plus" mark and basically are found when the CPL or KPL eyepieces are used with the Neofluar, Epi, or HD objectives. The phase ring in the phase objective provides for a very slight chromatic aberration (pink arrow). The Hoffman Modulation objective works best with the Nikon CFW eyepiece and therefore might be manufactured by Nikon. Similarly, the off-centered slit of the Hoffman objective causes slight chromatic aberrations with the rest of the Zeiss eyepieces and the Olympus FK eyepiece. Speaking of which, the Olympus FK eyepiece shows aberrations with all objectives as does the Nikon CFW eyepieces (with the noted exception above).

Why am I doing this?? I am interested in finding the best camera setup for the PM. I have read almost everything I can find on this site and others about focal and afocal, and I have experimented with every possible setup I have. But I also wanted to take out the affects of objective/eyepiece corrections, which led to this little investigation. I am waiting on the arrival of a 35mm lens and after that test, will post my camera results for suggestions and help in the camera section in a few days.

[Hobbyst46]

Thanks for the very interesting and relevant post.
What was the setup? Direct projection or afocal, which camera lenses?
Is the 35mm lens a camera lens ? For afocal tests?

I am asking because I am involved in a very similar task.

[Hobbyst46]

Maybe we are posting simultaneously - sorry. I see now that the same colored arrows appear previously and are explained.

[cmtalb01]

Thanks for your responses! Camera setup was afocal using a Sony a6000 with Canon FD converter and attached to a Canon Photomicro Unit F adapter. I was using a Zeiss KPL 10W eyepiece in the camera adapter which only views about 40% of what is seen in the eyepiece. I posted a picture of the setup shwoing the camera but it also shows a flash setup I was working with when the picture was taken. Flash was not used in the eyepiece testing.

The 35mm lens should arrive this week sometime and I hope to test it as well as I think it will give me close to 100% view in afocal setup. I have tried a Canon 50mm and Vivitar 28mm lens in this setup. So with a Sony's ASP-C sensor this is 35mm equivalent to 50mm, 75mm, and 42mm respectfully.

To date I have tested a number of setups, eyepieces, and lenses, including C-mount no eyepiece, C-mount with 0.5X lens, 5X, 6,5X, 7X, 8X, 10X, and 12.5 X eyepieces in both afocal and focal setups, and afocal (with 28 and 50mm lenses). Once I test the 35mm lens, I plan to post all the results in the camera section.

Thank you again for your feedback, I am also anxious to learn what your experience has proven. There are many, many posts, but from what I can find very little manufacture information. In addition, some of the adapters are 120mm, some different sizes. I did see one post that attempted to explain this, but I guess I will have to read that one again as I did not understand it at the time.

[Hobbyst46]

The 35mm lens should arrive this week sometime and I hope to test it as well as I think it will give me close to 100% view in afocal setup. I have tried a Canon 50mm and Vivitar 28mm lens in this setup. So with a Sony's ASP-C sensor this is 35mm equivalent to 50mm, 75mm, and 42mm respectfully.

I believe that you will succeed with the 35mm. The appropriate factor for your APS-C sensor (the same as mine in my Canon M10) is about 1.6.

I cite from others, for the afocal setup:
factor = eyepiece mag * the camera focal length(mm) / 250mm.

For a 10x eyepiece and a focal length 35mm camera lens - 350/250=1.4.

I am using a 8x KPL eyepiece with a 45mm camera focal length. Factor = 1.44. Not ideal but that is the lens I have. And I get very good coverage - 90% of theoretical.

I tried an old 50mm camera lens as well, coverage was roughly the same but the lens was manual only, so abandoned it.

I am also working on a simplified quantitative test to show CA in regions of the image, using ImageJ. probably something that has been invented ages ago, but I'm too lazy to check. You can see there the amount of chromatic aberration I got with various objectives, although the comparison was not as comprehensive as yours.

[Hobbyst46]

There are many, many posts, but from what I can find very little manufacture information.

In fact, there are some very good explanations including detailed guidance how to set-up the system, and I cannot specify names since many have contributed and I would hate to forget anyone. But Search recent posts, from years 2016-2018, on this Forum (very recent) and Photomicrography and Microscopy-UK, there are several excellent short articles.

My own personal experience is that of a beginner in photomicrography, its the first time I have used a camera on a microscope. My post with afocal results is still active (in "camera systems and imaging") and already enjoyed very cooperative and helpful feedback!