Using non-chroma-free infinity objectives

[aphi]

I've got my hands on a fairly nice objective, however, it is of European descent and as such it has very strong CA with an achromatic tube lens like the Raynox. It does seem to have a very large image circle though and it does retain resolution into the corners on full-frame, just only in one channel at a time at best.

So my assumption here is that the reason for this partial CA correction is to simplify the design of the tube and/or ocular lens, leaving some CA uncorrected and then using a non-achromatic tube lens to cancel the CA out.
If so, shouldn't the amount of CA be in more or less the same ballpark for all manufacturers with the same tube lens FL, since they're all using more or less the same glass types?

[Scarodactyl]

No, it is not. They have their own different formulae and they may vary even from one series to another by the same maker. Part of it is simplicity but I suspect a big part is keeping things proprietary within their systems.

[aphi]

Ah that's a shame. For more well-known series I suppose it would be possible to find out which tube lens P/N was used, but for the objective I have at hand here (Reichert/Leica Austria/AO Plan Fluor 20/0.4 XLWD) I was unable to even find basic specs and these seem to be very uncommon so I doubt many tube lenses floating around for these - plus the question of whether the tube lens would fully correct the CA or leave some for the ocular.

For posterity:
These Reichert objectives are part of a series for six-shot wafer inspection microscopes, "Polylite 88" (also goes by the name of Leica INM20). The mounting threads are M28x0.75 and the parfocal distance appears to be 50 mm, perhaps 2". The standard loadout seems to be
Plan Fluor LWD 5x/0.10 Epi
Plan Fluor LWD 10x/0.20 Epi
Plan Fluor XLWD 20x/0.40 Epi
Plan Fluor XLWD 40x/0.5 Epi
-- up to this point all objectives seem to have the same working distance, approx 15 mm (not measured, might be less) --
Plan Fluor 50x/0.90 Epi
Plan Apo 150x/0.95

There also appear to be 100x (Plan Fluor LWD 100x/0.70 Epi IK) and 2x objectives.

They all seem to have integrated concentric condensors (BD-type), despite the 150x not having an Epi marking.
Some are marked Reichert, some are Leica Austria.
They all have a chromed brass outer shell with what appears to be a glass-bead blasted stainless steel cover barrel in the middle which has the markings silk-printed.

Here's a Leica pamphlet: http://wie-tec.de/mediafiles/Sonstiges/ ... lta_hc.pdf (Content Warning: German language text)

Opening errors [spherical aberration], coma, and longitudinal chromatic aberration are advantageously corrected at their point of origin, i.e. in the respective component. For the correction of chromatic magnification difference (CVD) and astigmatism, however, a distribution of correction tasks between the objectives and eyepieces has proven advantageous early on [3]. Since the introduction of infinity optics, every microscope has a tubular lens system necessary for producing the real intermediate image, which - as previously described - can be used to create a specific correction state in the intermediate image [4], thus creating additional degrees of freedom.

With the DELTA optics in 1992, the compensation of objective CVD was shifted from the eyepieces to the infinity tube lens - another important step towards the HCS system. This provides particular advantages for the construction of large-field eyepieces.

So it could even be the case that the ocular is responsible for CA correction with these objectives.

The text goes on to explain that depending on the Leica system the eyepiece/ocular and tube lens have differing amounts of residual astigmatism and curvature of field to compensate for the objective aberrations.

So bottom line is: infinity objectives may be intentionally undercorrected for basically any aberration and might only produce a proper image with the original tube lens and eyepiece in the worst case.

[blekenbleu]

So it could even be the case that the ocular is responsible for CA correction with these objectives.

Yes, and Reichert expertise is available at microbehunter.com, e.g.:

When the merger between Wild-Leitz and Cambridge Instruments took place, there were at least 4 infinity corrected optical systems grandfathered into the merger.
There was
the c. 1950 AO 200mm Met system, utilizing 25mm objective threads. not sure of the parfocal distance or of the telan lens corrections.
the c. 1961 AO 200mm universal system utilizing R.M.S. objective threads. The parfocal distance was 34mm and there were lateral corrections in the telan lens. This system was also used at Reichert from 1974 on for certain models.
the c. 1965 Bausch & Lomb ~ 60mm parfocal universal system utilizing R.M.S. and 25mm objective threads. The telan lens applied lateral corrections.
the c. 1970 Reichert 45mm parfocal 200mm universal system utilizing R.M.S. and 28mm objective threads. This was also used by AO from 1985 on as R.M.S. The telan lens applies minimal lateral correction in this system; less than certainly the AO 34 mm system. Of interest is how similar it is to the older AO Apergon MET system. It would be interesting to try an Apergon objective in a Leica and see how it works.

The newly branded Leica company, utilized the Reichert 45mm parfocal system for their Delta optics, maintaining the 200mm tube length and level of corrections in the telan lens. They however, increased the objective diameter to 25mm, presumably in order to keep pace with the emerging requirement for U.W.F.. performance.

https://www.microbehunter.com/microscop ... php?t=8625
Subsequent discussion in that thread goes into greater detail on Reichert/Leica infinity corrections.

[Scarodactyl]

As I recall this particular Reichert industrial series doesn't do corrections in the tube lens (one of the only ones we have good test results for because Robert has compared several tube lenses includjng a Reichert one to others with a mitutoyo 5x objective). The eyepiece corrections aren't super strong on CA as I recall, mostly focused on planarity. I am not certain that these are identical to the later Delta optics, but I haven't handled these directly so I'd defer on that.

There's a reason that fully internally corrected objectives are generally favored for macro work. Corrections are a real pain to retrofit.

[aphi]

Appreciate the links and information a lot! I did search before making this thread but Google turned up either nothing / old eCommerce listings or lots of unrelated stuff for Reichert.

Sure enough, a Reichert tube lens is in this test of his: https://www.closeuphotography.com/tube-lens-test

My objective does have a lot of CA though:

100% center crop from Nikon Z7, Raynox DCR-150 focused to infinity (which results in slightly too much magnification with a field of view of about 1.6 mm, which would line up with the objective being meant for a 180mm tube lens)

Full frame corner crop. Also looks like astigmatism to me?

Looks terrible but red channel still has detail:

Another center sample:

[Lou Jost]

If the dominant image aberration is CA, you could still get great images by using monochromatic light.

[Scarodactyl]

Wow, that's rough. Maybe it is from a different series after all.

[aphi]

I've found two US patents for Reichert objectives:

https://patents.google.com/patent/US4384765A 100x/0.95 for 183mm tube lens
https://patents.google.com/patent/US4417787 50x/0.85 also for use with a 183mm tube lens

Both of these share a defined residual aberration:

It is an object of this invention to provide objectives well corrected for all aberrations except lateral chromatic aberration. The residual lateral chromatic aberration between 486.1 nm and 656.3 nm is 1% of the angular magnification at 589.3 nm across usable field.

The objective looks like this:

I believe the "IK" label means it is suitable for interference contrast microscopy ("Interferenzkontrast"), which was available as an option on the host microscopes.

[aphi]

I think I figured out (edit: obviously I didn't figure this out, I just found the explanation in the link below) why in Robert's test the Reichert tube lens performed nominally, yet Reichert objectives have significant lateral color.

https://www.microbehunter.com/microscop ... 188#p90188
https://patents.google.com/patent/US4715697A (Figure 1. VI, they're the last part of the optical path in the microscope housing, before the eyepieces)

There is a lens doublet with no net power after the tube lens which essentially only corrects for lateral color. So for use with a camera, a similar or identical doublet would be needed behind an achromatic tube lens like the Raynox.

Edit:
When I take the example shot of the corner crop and scale the red channel by 100.3 % while scaling the blue channel by 99.5 % I get them pretty well aligned with the green channel. That's almost, but not quite, the 1 % that has been claimed for the Reichert Austria objectives in the link; the difference could be because the red and blue channels of my camera differ from the Abbe number reference points that are used for the % lateral color.

[Lou Jost]

That's interesting. Reichert made a mirror objective, which (unless it has significant glass elements in it) would not have CA. I wonder if that 2-element doublet has to be removed when using that mirror objective?

[aphi]

So this objective came from an "Inspectron 880" marketed by the "Technical Instrument Company". It seems to be largely identical to the Polylite 88 and uses 10x WPK eyepieces [1], where the K means kompensierend, spezifikally kompenseyren der kromatishen aberration.

Meanwhile the Microstar IV above uses eyepieces with no "K" in the name (WF 10x, probably WeitFeld?), so probably non-compensating ones. That's why the MS IV has the compensation built into the bodies optical path, while it seems somewhat save to say that the Poly* series does not do that.

It would follow that the are no Reichert tube lenses with the required CA compensation.

[1] The head looks like it's different and sellers label it a confocal or fluorescence microscope, but that's of course extremely unreliable information and does not seem to make a ton of sense for a wafer inspection microscope.

[hans2]

Maybe you were already aware, but note that these are two different Reichert-branded infinity systems from around the same time. Microbehunter user wabutter who posted in the two threads linked earlier (among others) has referred to them as "Buffalo" and "Vienna". Summarizing from memory: The Microstar IV and Diastar are from a design group in Buffalo, NY that was originally American Optical and have 0.6% lateral color in the infinity space. The lateral CA is corrected mainly by the flat doublets in the eye tubes but there is some contribution from the tube lens as well. The Polyvar, Polylite, etc. are from a design group in Vienna, Austria (descended from the original Reichert) and have 1% lateral color in the infinity space. There are patents on the Buffalo body and Vienna objectives as you found but I am not aware of any patents on Buffalo objectives or the Vienna body and I have no personal experience with the Vienna stuff.

There are some confusing variations, for example comment #4 by Wayne in this thread about early production Vienna microscopes that used the mechanical design of the Buffalo heads with different optics, and also non-compensating eyepieces unlike the later iterations:
https://www.microbehunter.com/microscop ... 143#p86143