Correction Collar : Leitz [surprise]

[MichaelG.]

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I was rather surprised to find this “admission” by Leitz, and would welcome comments from the wise:
… perhaps the original German expresses it a little differently [?]
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IMG_9213.jpeg (339.06 KiB) Viewed 12986 times

Ref. https://earth2geologists.net/Microscope ... s_1967.pdf
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MichaelG.

[MichaelG.]

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316 views so far … and not a single comment
I am a little disappointed

MichaelG.

[erikwetterskog]

It’s fun alright! Maybe somebody at Leitz snuck that stuff into the manual after the final check.

A disgruntled optical engineer perhaps?

[MichaelG.]

Thanks for that Erik … I will sleep better now

MichaelG.

[PeteM]

I'd guess that something was lost in translation.

Perhaps, along the lines of: this won't be have any better resolution of a dry .70na objective used with exactly .17mm cover slips. But, if your cover slips are thinner or thicker, this will let you get them in sharp focus.

[apochronaut]

I think Pete is correct. .70 is not a particularly high N.A., barely more than the de facto .65 that are used daily in the 10's of thousands with no regard whatsoever as to cover slip thickness. The fact that it is a 63X objective , although it would on the surface seem relavent, isn't relavent, nor is the fact that it is an apo. Leitz is just being clever and putting an apo in the wheelhouse of multiple users, offering the correction collar when needed but noting that it will rarely be. Were it a .95 objective, that would be limiting and require a correction collar regularly. 70 is not limiting and is enough for 630X but not for use with 15X eyepieces.
We can get carried away with N.A., when it is not needed. There is talk of empty magnification but little of "useless N.A." Although a higher N.A. is usually attained along with a higher colour correction and results in a stellar objective especially where achromats are concerned, a higher colour correction can be obtained while keeping a modest N.A. too. This provides for a broader cover slip latitude and longer working distance, with superior ca & sa correction and resolution.
I use 3 objectives that fit this bill and each has no cover slip correction collar. The first is an AO 40X .80 planapo, 34mm parfocal. Can be used with 15X eyepieces to give 600X and even with a .22 cover it exceeds the resolution of a fine 40X .66 advanced planachro in the same family. The second is a Reichert 40X .70 planfluor, 45mm parfocal. It's just about the equal of the former, with slightly more cover thickness latitude. The third is a Lomo 40X .65 planapo, 45mm parfocal. A surprising objective. Functions just like a pedestrian 40X .65 achromat and can be used with both prepared and fresh thicker mounts, while providing great colour correction. I don't know about it's performance at 600X because I don't have any compatible 15X eyepieces but I have it's sister 60X .85 planapo anyway. Kind of an everyman's planapo.

[Macro_Cosmos]

That is totally BS, the effect can be demonstrated easily and 0.7 NA is already high enough to see the adverse effects of spherical aberration. Zeiss even made spehrical aberration compensation slides with a glass wedge.

Either during that time, imaging systems were lacklustre and thus the effect was minimal, it was a bad mistranslation, or someone was delusional enough to actually spew their copium into a manual.

[MichaelG.]

Thanks for the [overnight for me] burst of activity

MichaelG.

[hans]

I would guess "image sharpness" is referring to focus not spherical aberration and this is pointing out an advantage of their implementation compared to older or less sophisticated implementations where the correction adjustment changes focus at the same time? It would be an "ideal method of focusing when the thickness of the coverglass is unknown" because you simply turn the collar while judging image quality without having to constantly the refocus the microscope at the same time?

[Hobbyst46]

The same footnote #2 applies to the two dry planapo objectives, 40X0.95 and 63X0.95, on the previous page of that same Leitz catalog (p. 19, top table).

[apochronaut]

That is totally BS, the effect can be demonstrated easily and 0.7 NA is already high enough to see the adverse effects of spherical aberration. Zeiss even made spehrical aberration compensation slides with a glass wedge.

Either during that time, imaging systems were lacklustre and thus the effect was minimal, it was a bad mistranslation, or someone was delusional enough to actually spew their copium into a manual.

Evident at .4, thus only objectives under that and with a marked N.A./- can be used with or without a cover.
I'm not sure I would call it totally B.S. though, unless that stood for Basic Science. Achromats can be s.a. corrected only for one wavelength whereas a modern fluorite or apochromat use 4. Embedded front lenses patented by AO and the use of extra diameter lenses increase the axial diameter and reduce the s.a. at higher apertures.
Note even the presence of a Zeiss author at the end of this copied text and note the callout of 0.8 or greater.

Most objectives are designed to be used with a cover glass that has a standard thickness of 0.17 millimeters and a refractive index of 1.515, which is satisfactory when the objective numerical aperture is 0.4 or less. However, when using high numerical aperture dry objectives (numerical aperture of 0.8 or greater), cover glass thickness variations of only a few micrometers result in dramatic image degradation due to aberration, which grow worse with increasing cover glass thickness. To compensate for this error, the more highly corrected objectives are equipped with a correction collar to allow adjustment of the central lens group position to coincide with fluctuations in cover glass thickness. This type of correction is also used on objectives intended to be utilized with glycerin and water as the imaging medium.

Contributing Authors

H. Ernst Keller - Carl Zeiss Inc., One Zeiss Dr., Thornwood, NY, 10594.

Kenneth R. Spring - Scientific Consultant, Lusby, Maryland, 20657.

Brian O. Flynn and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.

[MichaelG.]

More detail from Leitz >> less comprehension

This, from one of the Heine Condenser leaflets is “interesting”

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source Right.jpeg (173.89 KiB) Viewed 8362 times

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All I can say is that the 63x is a very pleasing objective to use … its working distance is longer than that of the 10x … and the resolution is all one could reasonably hope-for at NA 0.70

Must build a blue/violet light source sometime !

MichaelG.