LOMO compensating optics

[Crater Eddie]

Yes, the seller assured me that they were 160 tube length before I bought them.
My first impression of these after playing with them a little tonight is "quite good".
For a quick comparison I chose a nice white cell in a field of red cells on a stained blood slide with coverslip, probably not the best subject, but I don't have any diatom slides.
Installed on the LOMO L-2-2 stand and paired with the eyepieces that I have at the moment:

LOMO WF10x/18 pretty good
LOMO 10x/18 noticeably better
Olympus WHK 10x/20 L best but not by much

The difference between the LOMO 10x/18 and Olympus WHK 10x/20 L eyepieces is subtle, the Oly's give just a tad flatter field, or so it seems.

Comparing the LOMO 40x Plan Apo to my Oly 40x Dplan, the Dplan is brighter and crisper, and provides a wider and flatter field. But the LOMO Plan Apo is still darned good. If I didn't have the Oly I would be very happy with it.
The working distance for the LOMO 40x Plan Apo is less than the Oly 40x Dplan.
Also, the 40x Plan Apo and the 60x Plan Apo are not quite parfocal, requiring about 1/4 turn of the fine focus knob when switching between the two.

That's all I have time for tonight. I'll work with them more over the next few nights with some pond samples, see what else I can turn up. It will be very interesting to compare the K-10x/18 eyepieces when I get them back.
It's funny, after using the Olympus BH-2 most of the time, I forget how much I like the LOMO L-2-2. With these new objectives I think I'll be using it more.

CE

[zzffnn]

CE,

In theory, plan apos should outperform plan achromats(like your Oly DPlans), at the same NA, when eyepiece compensation is not too far off. Edit: Sometimes CA from achromats may enhance apparent contrast at subject edges (making it seemingly crisper) and it can be hard to tell with (blue/purple) stained slides. Maybe try some live cells from buccal swab (under DIY oblique illumination) to see if your preference holds?

Your objectives seem to be the new OPA series (160mm tube indeed):
https://www.rafcamera.com/lomo-microsco ... 0x0-65-din

25-50 microns of parfocality difference is not out of the line with LOMO. You can buy parfocal shim rings to reduce that difference. I prefer color coded shim rings like these:
http://cynmar.com/accessories/25702-par ... it127.html
eBay also has some plain metal rings without color coding.

[apochronaut]

Comparing the LOMO 40x Plan Apo to my Oly 40x Dplan, the Dplan is brighter and crisper, and provides a wider and flatter field. But the LOMO Plan Apo
CE

I assume you mean that the plan part of the field is wider with the Olympus Dplan, not that the Lomo objective has a restricted field. The field diameter should be controlled by the field stop in the eyepiece.

Objectives are given a plan designation up to a certain field diameter and they sometimes don't even achieve that. Normally manufacturers would use the term semi-plan or microplan for objectives that fall short of the edge of the field slightly. You see microplan marked on some Baker/Vickers and Swift objectives. Reichert used semi-plan. Lomo would likely be less plan than Olympus, acting more as a semi-plan objective with a 20mm field, simply because the default W.F. eyepieces for them would have been 18mm f.n. and it is 20mm for the Olympus.

[Crater Eddie]

CE, In theory, plan apos should outperform plan achromats...

Yes, I had hoped the Plan Apo would out perform the Dplan, but as I'm mixing systems here I'm sure I'm not getting optimum performance from them. I guess it's not really fair to compare the objectives until I get the correct compensating oculars. But it's interesting to see how well the different eyepieces work with them.
You are very correct that this slide isn't the best subject for checking the corrections. I'll certainly try other subjects for better comparison as you suggest.
Thanks for the RAF link, that sure looks like it.
Those shim rings look just the ticket! I'll try that thanks!

I assume you mean that the plan part of the field is wider with the Olympus Dplan...

You are correct, the Oly Dplan is "more Plan" than the LOMO Plan Apo, I'm sure that is much of what I perceive as "better".
But there seems to be a tad wider field with one objective over the other, however since I have slept since then (and I'm not at home now to check) I can't say for sure which was which. I judge this by the fact that using one objective with a certain white cell centered in the field of view, I can see less than half of a certain other white cell at the very edge of the field of view, while switching to the other objective shows the entire white cell at the edge of the field plus a little bit more. True the two aren't quite parcentric, so I have to reposition the target cell to the center and I don't have an eyepiece reticle to get this perfect, but I'm pretty sure I'm getting it very close. Could it be that one of the objectives is giving a little less magnification, thus a larger perceived FOV? I didn't think of that until this morning. I didn't notice a difference in the apparent size of the cells between the two objectives, but it would be subtle. Maybe I should check this with a calibration slide?

CE

[MichaelG.]

... Could it be that one of the objectives is giving a little less magnification, thus a larger perceived FOV? I didn't think of that until this morning.

.
Bear in mind that 160mm is a mechanical tube length, and therefore [depending on the optical designer's preference] the intended primary image plane can be at various locations within the tube. This is one of the reasons why the performance with various eyepieces can be so variable. ... Some experimentation might be in order: If you are lucky, raising the eyepiece by a few mm may improve things. [lowering it is, of course, considerably more difficult] ... I would aim for the flattest achievable field, and then check the magnification.

MichaelG.

[Crater Eddie]

Bear in mind that 160mm is a mechanical tube length...

Ah, it boils down to mixing systems again, yes? Point taken, thanks.
CE

[Micro-Bob]

As far as I know parfocality is also influenced by the choice of eyepiece. So maybe this slight parfocality issue will improve with other eyepieces. You can check if parfocality improves if you lift the eyepiece by 5mm within the tube.

@zzffnn: Do you know the thicknesses of the parfocality rings? 25µ is not much.

[zzffnn]

As far as I know parfocality is also influenced by the choice of eyepiece. So maybe this slight parfocality issue will improve with other eyepieces. You can check if parfocality improves if you lift the eyepiece by 5mm within the tube.

@zzffnn: Do you know the thicknesses of the parfocality rings? 25µ is not much.

Yes, eyepiece changes parfocality and CE should wait for the correct EP.

This ring is supposed to be 25.4 micron thick:
http://cynmar.com/accessories/16868-PAR ... ASTIC.html

[Crater Eddie]

I thought it was odd that the 40x was not marked for cover glass thickness like the 60x is (see photos earlier in thread). Since it is not marked NC I figured that it is "understood" that the glass is needed. Of course I had to try it without the cover glass, and got the typical distorted image one might expect. Cover glass is definitely required.
CE

[MichaelG.]

I thought it was odd that the 40x was not marked for cover glass thickness like the 60x is (see photos earlier in thread). Since it is not marked NC I figured that it is "understood" that the glass is needed. Of course I had to try it without the cover glass, and got the typical distorted image one might expect. Cover glass is definitely required.
CE

.
I have no substantiating evidence regarding LOMO but: I think the fact that no cover glass thickness is specified simply means that the design is 'undemanding' as to the actual thickness [within the general range of cover glass thicknesses].

MichaelG.

[Crater Eddie]

So, those are still 160mm optics? Interesting that they would tone down the 40x to .65, which is highly unusual for a 4mm apo. Likely it has a greater w.d., than the more common high N.A. apos, which would definitely make it more user friendly.

Only other similar effort I have come across is the infinity AO/Reichert planfluorite( which works like an apo) at 40x .70. It has a greater w.d. than the Reichert 25x .65 planapo.

Looking at other LOMO long barrel Plan Apo objectives of this type, they all seem to have lower NA ratings than the corresponding shorty LOMO Apo objectives that I have seen. This is a little disappointing.
CE

[apochronaut]

There has been a tendency over the past 25 years or so, to reduce some apochromat and fluorite objective N.A.s though, so the lower N.A. of the Lomo 40x apo, might not occasion any necessary portent of mediocre imaging.
Not very long ago, an N.A. of .95 was almost standard for a 40x apo and it was more common to use high power eyepieces to achieve high magnifications without resorting to oil. The tradeoffs were short w.d., narrow f.o.v. and the necessity to resort to a funnel stop or buy in to an expensive iris diaphragm objective, to achieve D.F.
With the improvements in glass formulas, and more accurate ray tracing, overall resolution has become better at lower N.A.s., with objectives made by manufacturers that produce quality optics. I know for sure that a .70 N.A. fluorite can achieve the same resolution that was only expected with .95 formerly, because I use one . It has a relatively long w.d. It still can be pushed to 600x with a 15x w.f. and if I really want 8 or 900x dry, I can look for other objective options, rather than deal with the restrictions that a 20x eyepiece places on me. I also get stellar D.F. without having to have either a funnel stop or an expensive iris.

[MichaelG.]

I have just re-found this page, which includes a useful note about the Visual and Photo variants of the K7x eyepiece.
http://www.microscopy-uk.org.uk/mag/art ... photo.html

Slightly off the main topic of this thread, but I thought it worth linking.

MichaelG.

[Crater Eddie]

Christmas came a little early in the lab! I'll welcome any suggestions on ways to compare the corrections, I have pretty much just been flailing about on my own (obviously).
CE

[MichaelG.]

I'll welcome any suggestions on ways to compare the corrections, I have pretty much just been flailing about on my own (obviously). ...

The classic visual test of Achromatism seems to be Carpenter's "Disc of Deal"

Sorry ... I haven't had a chance to try it yet.

MichaelG.
.
.
https://archive.org/details/microscopeitsrev1875carp
Quoting verbatim from p207 of Carpenter's book:
"... The exactness of the corrections in lenses of these foci may be judged of by the examination of objects which are almost sure to exhibit Colour if the correction be otherwise than perfect. This is the case, for example, with the glandulæ of Coniferous wood (Fig. 223), the centres of which ought to be clearly defined under such objectives, and ought to be quite free from colour ; ..."

[Crater Eddie]

Thanks for the link, that looks like a very interesting book. Time to do some reading.
CE

[apochronaut]

I usually use a high contrast slide, or a measuring grid. Something with distinct dark on light elements. I have a boar tusk section. It is good because it has distinct striations and it's thickness is around optimum. Try to choose a sample with limited natural diffraction and the appropriate thickness.

Older systems but less so with compensating eyepieces, often had eyepieces corrected better for certain objectives than others in the range. It used to be that, in order to have as close to perfect corrections as was possible, each objective would actually need a slightly different eyepiece. Cost and convenience factors prevailed however, so in practice, the optimization hovered around the 40X objective and only one eyepiece design was used. As objective and eyepiece formulae have evolved, this is not normally the case now. I am not sure where the Lomo systems sit on that continuum, so I would do all my assessments using the 40x. It is possible the 60x may vary slightly, from the results with the 40x.

You are looking for on axis ca and lateral ca.

If you see any but very slight, chromatic aberration on axis using an apochromat , I would question the corrections, and certainly, if you can get less ca on axis with any other eyepiece but even apochromats can display a very small amount of ca on axis with certain samples and it is almost always a pale lavender or lavender pink. Micron wide circles or channels, will be lavender, whereas with an achromat, they will be orange red inside the structure and blue outside, usually.
Any variation from an optimum condition of correction, should be pretty obvious. You are mainly looking for chromatic aberration. I wouldn't worry about spherical aberration; any of that would be extremely slight.

With the criteria above , when a grid line viewed with an achromat, has minimum ca bordering it when placed in the center of the field and does show ca ( usually orange outside and blue inside) when shifted to the periphery, it might easily be within spec. With an apochromat, it isn't.


Apochromats, when viewed with an overcorrected eyepiece, will be orange to the outside and blue to the inside at the periphery, while seeming quite well corrected on axis. With an undercorrected eyepiece the colour banding will be reversed.
Even older non-plan apochromats , while displaying slight lavender chroma on axis, while they will need refocusing at the periphery, should still display a degree and colour of chroma consistent with the on-axis performance, when used with a well corrected eyepiece. Often though, if an eyepiece of a wider field of view than that of the original supplied for the objective is used, despite being well corrected for the objective, increased chroma can result outside what would have originally been the limit of the f.o.v. An instance would be using a well corrected 10X eyepiece of a 20mm f.o.v., with an objective that originally used a 10x eyepiece of a 13mm f.o.v.

[Crater Eddie]

Thanks very much for that Apo! I do have a calibration slide with both scales and grids, I'll give that a whirl.
I played around just a bit yesterday, enough to learn that the 40x and 60x Plan Apo objectives are still not any more parfocal with these compensating eyepieces than the others that I already had (as mentioned earlier in this thread). Looks like I might need one of those shims after all.
CE

[Micro-Bob]

You might have a look whether your calibration slide has a cover glass over the actual scale. Your test wouldn't be very useful if you test an objective for 0,17mm cover glass thickness with an unvovered calibration slide.

[Crater Eddie]

You might have a look whether your calibration slide has a cover glass...

Thanks for the heads-up, I hadn't thought about that.
I have gotten side tracked from this project with some other issues in the illumination system, will hopefully get back on track soon.
CE

[apochronaut]

The issues you will be facing, regarding eyepiece/objective matching are going to be lateral ca. Cover glass or no cover glass won't affect that but having to make a judgment on images that have spherical aberration, could be a little straining. You will need strain free eyeballs.

[Crater Eddie]

MY eyeballs haven't been strain free since about 1968.
CE

[Crater Eddie]

Ok, here we go.
Testing the 40X LOMO Plan Apo DIN objective with the various sets of eyepieces that I now have, I must say that for the most part the differences from one set to the other are subtle.
The most obvious difference right off the bat is that the K10x/18's provide a hint of a tan-ish cast to the background as does the B&L 10x Compensating eyepiece that Charlie G was kind enough to send to me, all the other eyepieces provide a greenish tint, neither of which I would ever have noticed had I not been comparing them side by side. A difference in the coatings perhaps?
Observing a live diatom on a wet slide, all eyepieces provide a nice view but with a tinge of color at the edges and in the fine details. The K10's exhibit the least tinging and provide a bit more contrasty image, resulting in a bit more fine detail, at least to my eyes.
So for this the LOMO K10x/18's rate the best, followed by the Olympus WHK 10x/20L, B&L 10x Compensating eyepiece, then the LOMO 10x/18, and the LOMO WF10x/18 coming in last. But again, the differences are subtle. I would be pretty happy with any of these if I didn't have the others to compare them with.

Since I don't have a counting chamber, the next test was observing the grid on a calibration slide (with cover glass), still using the same objective:

LOMO K10x/18 = faint yellow/orange tinge at the outside edges of the lines, and a blue tinge at the inside edges. But these are all quite faint and narrow near the center of the field of view, becoming slightly more pronounced towards the outer reaches.

Olympus WHK 10x/20L = practically identical to the above

Charlie G's B&L 10x Compensating eyepiece shows the least color tinging of all of them (practically none) and much better consistency from center of field to the edge. But it has a narrower field of view and pretty short eye relief.

LOMO 10x/18 = similar to the Oly's but a little worse

LOMO WF10x/18 = the worst of the lot... not terrible at the very center, but deteriorating rapidly from center out towards the edges.

All exhibit the same color tinging on the same edges, so I suppose all are "over correcting" to some extent?

Such is my very unscientific comparison, in case someone might find it in any way useful or amusing.
CE

[zzffnn]

Nice work, CE, thanks for sharing. Your finding makes sense too. And yes, the LOMO K10x/18 does add a slight tan cast.

Do you have a LOMO dedicated immersion darkfield condenser? If so, doing a similar test under darkfield may reveal slightly more optical distortions. But the ranking would likely be the same.

I wonder how the short barrel Olympus WHK 10x eyepiece would fare. I did not test it against LOMO K10x/18 with LOMO apo objectives, but did test both EP with an AO 160TL phase contrast objective and covered calibration slide. They seemed close and pretty decent except for the very edge (neither was perfect, though good enough for my casual use).

[apochronaut]

Interesting stuff to me. What I wonder is: do your apochromats differ significantly from Lomo achromats in the degree of ca, either axial or lateral, when used with Lomo eyepieces?

[Crater Eddie]

Thanks fellows! This has been a lot of fun.

Do you have a LOMO dedicated immersion darkfield condenser?

No, I don't have the LOMO darkfield condenser, sorry. Maybe some day.

...do your apochromats differ significantly from Lomo achromats in the degree of ca, either axial or lateral, when used with Lomo eyepieces?

I tried the 40x achromat objectives with the K10x eyepieces, and I have to tell you that the difference at the center of the field of view is not dramatic. The Plan Apo is better, but not dramatically so. I thought it would be a bigger difference.
CE

[zzffnn]

A thick diatom under oblique light may reveal more difference in CA.

Under extreme oblique provided by Leitz Heine condenser, my LOMO 10/0.40 achromat gave massive purple fringe around most diatoms, my short LOMO apo 10/0.3 gave no false color at all. DIY oblique using a regular condenser may reveal less difference, but you should still be able to see it.

Such a difference is important to me, because I use oblique a lot. If a microscopist runs mostly plain brightfield and rarely oblique, then price difference may not be worth it.

[Crater Eddie]

Admittedly this was just a quick look with a single subject. Most likely part of the issue is lack of knowledge on my part. I'll play with this over the winter with different specimens, see what I can learn.
CE

[apochronaut]

Some modern Apochromats do not need corrective eyepieces. Nikon CF objectives are one such type. For others, and that includes all older ones, made up until the mid-80's roughly, a matched corrective eyepiece is absolutely imperative, otherwise the objective ceases to function as an apochromat. I n other words, the apochromatic nature of the image, results from the performance of a system; not as the result of the performance of a device called an objective. You can't assess the function of an uncorrected apochromat, unless you are using an eyepiece that is a precise corrective match and that would mean an under-corrective match.

Apochromats that are functioning prperly, should image colour fringe free, with only a hint of lavender or pink, where higher levels of diffraction occurs. If they do not, then they are not functioning as apochromats.
With accurate correction, the higher N.A.s associated with their construction as well as their freedom from the adverse effects of uncorrected diffraction, results in higher resolution and as an offshoot of that, more relaxed viewing and less eyestrain. It becomes, " oh, look at that", instead of " I wish I could see that better" and then a bump in magnification in order to,.... hopefully .

The fact that the Wild 6xK eyepiece seemed to be the best overall, implies that the other Lomo eyepieces are not a match. They can't be an almost match, or it can't be a case of Lomo not quite hitting the button, when it comes to correction and Wild being better at it. There must be some other Lomo eyepiece out there or composite optical system, that was so designed for that objective.

Corrective eyepieces for apochromats will have a colour fringe around the field stop that is yellow to orange. Different corrective eyepieces will have slightly differing hues, indicating the degree of undercorrection that they are designed to provide, which will precisely match the overcorrection in the objective. Any eyepiece with a blue fringe, is an overcorrected eyepiece and has been designed to correct for the undercorrection associated with the inadequacies of achromats. Any eyepiece, one might come across that has absolutely no colour fringe at the perimeter at all, is an uncorrected eyepiece and would be designed to be used with an objective that requires zero correction, such as the Nikon CF or Olympus D planapo. Eyepieces for Leica HC objectives, should also be colour fringe free, since Leica has built and refined their system based on the needed lateral chromatic aberration and astigmatism corrections taking place in the tube lens, rather than in the objective, a design characteristic brought forward from the origins of Leica's infinity system, which was the AO/Reichert system.

Is it possible that those Lomo objectives require a corrective tube lens, designed so that the conventional eyepieces could be used with them?

[Crater Eddie]

I get what you are saying. I'm sure that it is quite possible that these objectives need either a different set of compensating eyepieces, a different viewing head, or some other missing piece of the optics train. I suppose this is what I get for playing with the oddball LOMO stuff, insufficient knowledge base and little to no documentation.
It is rather like a 1000 piece jigsaw puzzle with no picture on.
CE