Potentially Missold Lomo Objectives

[Cactusdave]

Stimulated by the comment on the dubious 'Mitutoyo' objective it's perhaps worth pointing out that there are a lot of Russian Lomo objectives offered on Ebay as 'Apochromat' and 'Planapochromat' which certainly aren't. The Cyrillic labeling used by Lomo for these quality of lenses is quite clear. Check here for the expected designation on Lomo planapos http://rafcamera.com/en/microscopes/obj ... biological and here for apochromats http://rafcamera.com/en/microscopes/obj ... biological . I have no connection with this vendor, who also sells on Ebay, but he is a relaible supplier of Lomo objectives, which when correctly identified, can be of good quality for a reasonable price. Mostly these objectives are 'short' non-DIN standard length and will need an extender to be anywhere near parfocal with newer DIN objectives, or even sometimes, to reach focus at all.

There is a possiblity that the use of an extender will somewhat compromise optical quality. I have never been clear on the possible extent of this. I am aware that Leitz made a special adapter containing a supplementary lens to allow their high quality (fluorite, apochromat and planapochromat) pre-DIN objectives to be optimally adapted to their later DIN microscopes, but the eqivalent adapter for achromats and planachromats had no glass.

[dolmadis]

Hi Dave

What a great useful post.

I have also seen a rash of 190mm Lomo objectives on Ebay and I am wondering if you would be able to comment on the usefulness of these and on what stands that they can be used?

Thanks


John

[Cactusdave]

I think the 190mm objectives were most likely made for episcopic use on a Lomo metallurgical microscope with a 190mm tube length. Some come with a mount for a single objective changer typical of this sort of application. They will probably have a non RMS thread size. Though adapters for these odd threads to standard RMS can be found I have no idea what the optical quality would be like, as the lens would be operating significantly outside its intended use. I cannot find any reference to their use on a 160mm tube length microscope with a quick Google search.

It is also as well to be aware that Lomo made a significant number of infinity corrected objectives. These turn up frequently on Ebay, as do similar objectives from Zeiss Jena. The usual infinity symbol is always engraved on the barrel, but it can be difficult to see sometimes in seller's photos.

[Ichthyophthirius]

Hi Dave,

Good point. One of the sellers has a number of incorrectly described objectives (somebody should tell her); it should say "АПО" on the engraving, otherwise it's not an Apo.

When using a Lomo objective (160 mm tube length; 33.5 mm parfocal length) with an extender without compensating lens, spherical aberration can become a problem. There are different ways of calculating when the spherical aberration becomes noticable, one of them is plotted here: http://www.science-info.net/docs/etc/Tube-Length-na.gif

Worst case: Using Lomo objectives on a Zeiss Standard microscope with a 11.5 mm extender to match the Zeiss parfocal length (45 mm) and using Zeiss DIN eyepieces (10 mm eyepiece parfocal length; Lomo: 12.5 mm). The tube is now 14 mm too long (11.5 mm + 2.5 mm).

This means that all Lomo dry objectives with NA >0.5 and oil objectives NA >1.1 used with these extenders won't perform well on this microscope.

The Leitz adapter rings for conversion of 37 mm parfocal length to 45 mm all had a compensating lens of a focal length of f = -3000 mm. If an adapter doesn't have such a lens, the lens is either missing or it isn't such an adapter. There was no special version for achromats, just the standard version for all objectives (achromats and apos), a special version for fluorescence and a version for polarisation. All of the early Leitz planachromats started with a parfocal length of 45 mm, no 37 mm versions were ever made.

Regards, Ichthy

[Cactusdave]

Thanks for the extra information about where problems with extenders are likely to occur. Thanks also for the clarification about Leitz extenders. I have seen only two versions. One marked just PLEZY. I have never seen one of these with a lens in it. The other marked PLEZY-Flu which does have a lens in. I assumed the Plezy-Flu was for more highly corrected objectives, in fact I thought I had read that somewhere. You say this was especially for fluorescence applications (presumably with high numerical aperture objectives)?

[Ichthyophthirius]

Hi Dave,

I have both adapters as well. They all have lenses in them. From this and from the Leitz catalogues, the simple PLEZY contains a weak -1/3 dpt lens. I think yours was removed by the previous owner (unless there has been a version for infinity-corrected objectives; but I have never seen one in the catalogues). This can be used for all objectives, including fluorite and apo lenses.

The PLEZY-Flu is for fluorescence microscopy (usually this means special glass with low autofluorescence and high transmission). It is the same weak, single lens, so it doesn't have any special correction properties.

Regards, Ichthy

[Cactusdave]

Thanks Icthy. That's very clear. Will the PLEZY with glass improve the performance of all objectives that need an extender or only Leitz?

I must dig out some diatom images that I took with high magnification, high NA Lomo lenses, including apochromats with a simple extender on a Zeiss Standard. I don't recall the spherical aberration as too bad, but I do recall some chromatic aberration even with a Lomo compensating eyepiece.

[Pau]

Just to add a point: short barrel is not a standard. I bought a Leitz PLEZY FLUO for use a short Nikon I have in the Zeiss Standard and it cant't focus, it's still too short to achieve 45mm parfocal distance (it works well in a Oly CH clone that has not a fixed upper focus limit despite bundled with DIN objectives). I don't have any Leitz short objective, but they must be longer than old Nikons

[Cactusdave]

The old Nikon objectives for the Nikon S series are indeed very short, and need a longer extender. I have a short Nikon X40 Apo of this type that is in fact very good with a long enough extender without any very bad aberrations.

I have found some diatom images taken with this Nikon and the Lomo X40Apo 0.95 dry, X70Apo 1.23 water immersion and X85 1.0 water immersion objectives. I'll put them in a separate thread

[johan]

... here for apochromats http://rafcamera.com/en/microscopes/obj ... biological.

Dave, the second of those links doesn't work, it leads to a 404

[Cactusdave]

Thanks Johan. Link now edited and it works. An extra full stop got into the URL.

[Ichthyophthirius]

Will the PLEZY with glass improve the performance of all objectives that need an extender or only Leitz?

Hi Dave, The PLEZY adapter should work with all finite tube objectives (with the usual intermediate image distance of around 150-152 mm), regardless of the manufacturer. The only problem could be hot-spots/reflexions in very unfortunate cases. The adapter will extend the parfocal length by 8 mm. When used with 37mm parfocal objectives, it will maintain parfocality with 45 mm parfocal objectives on the same microscope.

The adapter improves the performance compared to a simple adapter ring without a compensating lens. However, it does (slightly) decrease performance compared to not using an adapter at all ... as any additional lens in the optical path will decrease performance!