Leica 1750 Plan 10Ph/0.25 objective "repair"

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hans
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Leica 1750 Plan 10Ph/0.25 objective "repair"

#1 Post by hans » Mon Jul 05, 2021 9:04 pm

Continuing from: https://www.microbehunter.com/microscop ... 06#p106315

I put "repair" in quotes because I don't think there there was anything wrong with it until I accidentally dumped out all the lens groups after removing the rear baffle (which was also the retaining ring!) to bet better access for cleaning. Let's hope the eBay seller is not on here to see the fate of the objective. I actually did make some attempts already to fix it. Reassembled several times randomly and one of the alignments gave a not-obviously-terrible image but still some noticeable asymmetry in the PSF.
apochronaut wrote:
Mon Jul 05, 2021 11:33 am
That looks like it might be in the rotation of the second cell...
Interesting you say that because there actually are holes like patta mentioned that access the second cell. (One original hole visible on the far left in the attached photo.) I also drilled access holes to the other cells but was rotating the cells in place was difficult. (Soft probes slip but hard ones leave divots/scratches that cause the cells to bind.) However just now I realize, probably what you are supposed to do (and why there were two opposing hole originally) is use two probes with balanced force from both sides to avoid binding. I will drill a second set of the larger access holes on the other side and try that when I get a chance.
apochronaut wrote:
Mon Jul 05, 2021 11:33 am
...that is pretty bad.
Yeah, I didn't disbelieve the warnings, but was surprised just how bad it was.
apochronaut wrote:
Mon Jul 05, 2021 11:33 am
If you are really lucky , you can sometimes find the complementary are on the barrel that caused the scratches and get a cell to barrel alignment.
Didn't notice any, I will check, but not hopeful because the tolerances are not that tight and everything slides in/out freely.
apochronaut wrote:
Mon Jul 05, 2021 11:33 am
Unfortunately, there is no easy way of getting the shim order and location correct, once shuffled.
No shims, luckily, just one large spacer which I'm pretty sure has to go between the 2nd and 3rd cells.
apochronaut wrote:
Mon Jul 05, 2021 11:33 am
...try fiddling with the diaphragm/annulus relativity. Some of that image skewing might get taken up with a DF centering adjustment.
Didn't notice any effect while setting up DF, and the image looks terrible in BF also. I did the DF on dilute milk mainly because it nicely shows the shape of the PSF.
patta wrote:
Mon Jul 05, 2021 12:23 pm
The coma may be fixable: remove the skirt; loosen a bit the screw that holds the lens pack. Toward the end of the objective, there are usually four little holes. With the objective mounted, observing the milk, fiddle a bit inside those holes, like with a toothpick; there is a loose lens inside that can fix collimation.
I will try again rotating the cells with two probes as I just mentioned above. There are no set screws at the front, retaining ring at the back is all that holds the whole thing together, so it seems like rotation is the only adjustment originally possible.
patta wrote:
Mon Jul 05, 2021 12:23 pm
http://www.funsci.it/files/obbiettivi.pdf
(Sorry it is a pdf, and in italian. see illustration at pag. 56 for example)
Looks interesting, thanks, and machine translation seems to be doing a reasonable job on the parts I tried so far.
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Re: Leica 1750 Plan 10Ph/0.25 objective "repair"

#2 Post by apochronaut » Mon Jul 05, 2021 10:55 pm

I hadn't seen the objective. That looks to be different than the ones designed in the Buffalo factory. Some of the Buffalo ones, the better designs used a thread on bezel for the front lens, rotationally aligning the rest of the lens cells in a jig, then filling the barrel like a sausage. The standard AO design for their cheaper objectives was to align them all in a jig and then load them in like stuffing a sausage. The cells went into the barrel very snugly, so no alignment was really possible nor necessary, except rotationally.
That one looks like they may have transferred over a design from Germany or a more likely possibility is India. The ATC 2000 production went to India at some point, made in the same facility as some Labomed microscopes. Is the machining a bit coarse? Not like a Microstar objective? The early ones said Made in U.S.A. on the rating plate. The Indian ones say Assembled in U.S.A. The finish on the objectives took a nosedive.

Those alignment holes need to be 4, do they not? Were they not plugged?

hans
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Re: Leica 1750 Plan 10Ph/0.25 objective "repair"

#3 Post by hans » Mon Jul 05, 2021 11:10 pm

apochronaut wrote:
Mon Jul 05, 2021 10:55 pm
The ATC 2000 production went to India at some point, made in the same facility as some Labomed microscopes. Is the machining a bit coarse? Not like a Microstar objective? The early ones said Made in U.S.A. on the rating plate. The Indian ones say Assembled in U.S.A. The finish on the objectives took a nosedive.
Yeah, definitely cheaper construction than the 400-series objectives with fairly crude (inkjet printed?) markings, even sloppier-looking than the printing on the 400-series ones. I only have the one objective, no ATC2000, and there is no country of origin marked on it, unless it wore off.
apochronaut wrote:
Mon Jul 05, 2021 10:55 pm
Those alignment holes need to be 4, do they not? Were they not plugged?
Only two originally, exactly opposite each other, and they are just empty, unthreaded holes. No sealant or adhesive of any kind anywhere. Everything just dumped out freely as soon as I turned it over.

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Re: Leica 1750 Plan 10Ph/0.25 objective "repair"

#4 Post by patta » Tue Jul 06, 2021 3:51 am

I was expecting 4 holes too.. instead, now there are more!
The original holes, my understanding is that are made to push the lens inside, not rotate it. But only two holes? Maybe are for rotating indeed. Well, now you have many more holes!

A faster but unscientific method that may fix the coma for loosely built optics: little kicks.
With the objective mounted, lens pack almost fastened. Hit it it softly on the sides with some steel tool (not a sledgehammer; the 13mm wrench recommended); Look at the image; kick left, kick right, you may kick the coma out of there. I can clearly imagine the "Quality Control guy" in India doing that fix for each objective before shipping.

BTW the lenses most sensitive to misalignment should be the last ones (the ones near the mount), the two little meniscuses facing each other, need to be really facing each other. Why Plan are so much more expensive.
Edit: Or maybe not, different design

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Re: Leica 1750 Plan 10Ph/0.25 objective "repair"

#5 Post by hans » Tue Jul 06, 2021 8:46 pm

My impression from the fiddling so far is that lateral shifts were not having much effect, while some rotations clearly were. Not sure how plan this really is, it appears to be a simpler design with not as much glass in it compared to the Reichert 1742 10X phase objective for the 400 series, maybe it is more like what is sometimes called semi-plan?

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Re: Leica 1750 Plan 10Ph/0.25 objective "repair"

#6 Post by apochronaut » Tue Jul 06, 2021 10:36 pm

AO had a series of plan objectives beginning in the early 60's. As time marched on, they got better and better, with wider better corrected fully plan fields. In the early 80's, they had to add lenses out the back of the 34mm barrels in order to get more lenses in there to do a better job because there was not enough space inside the 34mm barrels. In the next incarnation, either they included more fluorite glass or some newer synthetic formulations came available because the extra lens disappeared but the performance improved yet again, however they still filled the barrels. When the planapos came out in 1984, the barrels were full but they never released a 100X planapo. My guess is that they couldn't fit the required number of lenses in those barrels.

Then a strange thing happened. The next plan achros in 34mm barrels they kicked out had acceptable but only average performance but the amount of glass in the objectives was much less. By that time they had moved on to 45mm barrels with improved planachros yet again so that last generation of 34mm objectives were primarily for service support of existing 34mm infinity based microscopes. Modern glass formulas had allowed them to make an affordable , infinity corrected plan achro objective with which to service older microscopes. Modern glass formulas had also allowed them to make a first rate plan achro for the series 400 microscopes. If you pick up one of the last 34mm planachros, the ones that just say Made in U.S.A. and a cat. # 1734 planachro; the latter weighs about twice as much.

When the ATC 2000 came along as an excellent replacement for the 150, it was offered with either achromats or planachromats. It was a student microscope. Where did those achromats and planachromats come from? It was an infinity corrected microscope. Best answer is that they were the 34mm #1076-1079 40 year old achromats , spruced up a bit and tweaked into 45mm barrels and the planachromats were those latter generation 34mm budget planachros, tweaked into 45mm barrels.
When the production went to India, the lens formulas did too but India has a whole different settup for the production of the barrels and a different group of craftsmen with a somewhat different skiilset. They have been aligning objectives differently for 5 decades. Same lenses, different objective barrels and alignment procedure.

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Re: Leica 1750 Plan 10Ph/0.25 objective "repair"

#7 Post by hans » Wed Jul 28, 2021 4:52 am

Got this out and messed with it some more...
apochronaut wrote:
Mon Jul 05, 2021 10:55 pm
Those alignment holes need to be 4, do they not?
patta wrote:
Tue Jul 06, 2021 3:51 am
I was expecting 4 holes too.. instead, now there are more!
The original holes, my understanding is that are made to push the lens inside, not rotate it. But only two holes? Maybe are for rotating indeed. Well, now you have many more holes!
Yeah, there were 4 holes originally, not sure how I got confused about that. Now there are 12 total and I deburred and smoothed out everything with a small scraper so things move more easily. The middle cell is a little undersize relative to the others and shifting does have the largest effect but it seems like rotation is having some effect too. The final cell doesn't do much so seems like relative shifting/rotation between the first two closely-spaced cells is most important, probably not surprising.

Shifting the second cell to get symmetric PSF in the center of the field is not difficult. When I first did that with the cells in random orientations the behavior around the periphery was far from symmetric -- looked like fairly pure astigmatism at one edge but a lot of coma mixed in at the other edge even though there was no coma in the center. I then messed with rotating the second cell but using two probes through the access holes it is impossible to get pure rotation of either of the first two cells without shifting the second, so a little hard to tell what is going on. Also hard to keep track of how far I am rotating. In any case, after a lot of messing around with rotation followed by recentering it is now in an orientation where the behavior around the edge is much more symmetric looking mostly like astigmatism with a little come mixed in all the way around.

I will take some photos eventually but first wanted to ask about the astigmatism. None of the messing around with any of the three cells has caused a significant amount of change in the average astigmatism around the periphery and it is quite a lot, maybe 2-3X what the 1732 10X plan achro for the 400 series shows. It is reasonably plan going by circle of least confusion, not obviously worse than the 1732, but much more astigmatism. So any thoughts whether the astigmatism is:
  • Somehow still due to incorrect reassembly even though the image is now good in the center and none of the cell shift/orientation seem to affect it.
  • A design compromise made in the lower-cost plan objectives. (Design is clearly simpler than the 1732 so something has to give, I think.)
  • A mismatch between the 400-series heads/eyepieces. I have found almost no information on the ATC 2000 optics.
???

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Re: Leica 1750 Plan 10Ph/0.25 objective "repair"

#8 Post by hans » Wed Jul 28, 2021 6:03 am

hans wrote:
Wed Jul 28, 2021 4:52 am
A mismatch between the 400-series heads/eyepieces.
Meant to say with not between.

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Re: Leica 1750 Plan 10Ph/0.25 objective "repair"

#9 Post by hans » Fri Jul 30, 2021 6:19 am

There is really only one arrangement of the lens cells that makes sense but I tried some others just in case and they were all much worse, as expected. So now pretty sure it is assembled correctly and the astigmatism is either the normal performance of the cheaper design or maybe a correction mismatch with the 400 head. PSF looks ok in the center viewing small particles in darkfield, not obviously worse than the 1732/1742 10X objectives designed for the 400 series. However the phase contrast effect is not very good in a MicroStar IV. The diffraction ring in the objective just barely covers the condenser annulus, there is a fairly strong brown tint, and the phase effect fades out into more of an oblique effect toward the periphery.

First photo is with the 1750, third is a 1742, both with exactly the same neutral processing profile which is fairly close to the view through eyepieces. Second photo is the same 1750 shot as the first but with color balance and tone curve adjusted to match the 1742 photo.
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1750-neutral.jpg
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1750-adjusted.jpg
1750-adjusted.jpg (195.08 KiB) Viewed 5029 times
1742-neutral.jpg
1742-neutral.jpg (202.6 KiB) Viewed 5029 times

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Re: Leica 1750 Plan 10Ph/0.25 objective "repair"

#10 Post by hans » Fri Jul 30, 2021 7:58 am

Some darkfield shots showing the similar center performance but worse astigmatism, file names are descriptive. No real obvious lateral CA mismatch for the ATC 2000 objective in the MicroStar IV but might be hard to tell with the astigmatism. Ignore the magenta color artifacts in blown highlights, I get that converting Panasonic files in RawTherapee, never noticed it before with my Nikon and haven't looked into it yet.
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1750-df-center.jpg
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1742-df-center.jpg
1742-df-center.jpg (113.9 KiB) Viewed 5016 times
1750-df-astig.jpg
1750-df-astig.jpg (84.78 KiB) Viewed 5016 times
1742-df-astig.jpg
1742-df-astig.jpg (111.69 KiB) Viewed 5016 times

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Re: Leica 1750 Plan 10Ph/0.25 objective "repair"

#11 Post by patta » Fri Jul 30, 2021 9:52 am

They're nice, congratulations! Darkfield at the center is just fine. It is a crop of the whole field, right? While the astigmatism photo, a crop of the corners?

Astigmatism, that may not be fixable, but, with some center cropping, voila, digitally eliminated! I've read somewhere that Leitz (then Leica) had heavy astigmatism correction (or compensation?) in their Periplan eyepieces. Check now... yes, I can confirm that, the reticle in my Periplan eyepiece show pretty heavy astigmatism. And negative field curvature. I've never noticed before!! While together, matched Leitz objective+eyepiece, no astigmatism. Maybe they still do the same trick, leave some heavy astigmatism in the objective. Of course it isn't written in the marketing brochures...

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Re: Leica 1750 Plan 10Ph/0.25 objective "repair"

#12 Post by hans » Fri Jul 30, 2021 3:52 pm

Yeah, crops from the same two photos, close but not exactly center and edge. Centering is a little off between two objectives and I adjusted positions to select nice clusters of cells and correct the centering in the crops.
patta wrote:
Fri Jul 30, 2021 9:52 am
Maybe they still do the same trick, leave some heavy astigmatism in the objective. Of course it isn't written in the marketing brochures...
Yes, not nearly as much documentation or experiments around on presence of field curvature and astigmatism in the intermediate image as there are on lateral CA. I took a photo of a grid in the image plane the eyepiece used in the MicroStar IV a while ago: Reichert 181 eyepiece field curvature Do you have a reticle that goes all the way to the edge of the field? Most I have seen only have stuff in the central ~1/2 of the FOV, hence the shortened eyepiece. (Actually that exact eyepiece is the one used in these photos -- the little extra wobble due to the shortening is not a problem when sitting vertically on the trinocular head.)

In that thread Viktor mentioned similar observations with Nikon CF objectives:
viktor j nilsson wrote:
Mon Aug 03, 2020 6:06 pm
apochronaut wrote: Nikon doesn't admit to that in any literature and I don't have the parts handy but I did note that they also make a CWD eyepiece that they vaguely recommrnd for low power CF planapo objectives. The translation is murky but it seems that they are different somehow. If there are is no ca compensation required, then the CFD must be correcting for something else differently, than the CFW. Field curvature? I was hoping Viktor could answer that question better.
I wish I could give a definitive answer but I can't. It is true, however that all the low-power CF PlanApo objectives are rather poor in the corners when used with direct projection on an APS-C sized sensor (~26mm.diagonal). This is well documented. See, for example, here:

https://www.closeuphotography.com/4x-te ... objectives

This is not fixed by stacking, so it is not only caused by field curvature.
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1750-df-fov.jpg
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1742-df-fov.jpg
1742-df-fov.jpg (129.87 KiB) Viewed 4976 times

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Re: Leica 1750 Plan 10Ph/0.25 objective "repair"

#13 Post by hans » Fri Jul 30, 2021 9:35 pm

Since the Leica 1750 is apparently not a good match for the MicroStar IV I should get rid of it before I am inevitably tempted to buy an ATC 2000 out of curiosity. Anyone have an ATC 2000 and want it, free? I would be curious to see how the image looks in the correct stand.

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Re: Leica 1750 Plan 10Ph/0.25 objective "repair"

#14 Post by patta » Sat Jul 31, 2021 5:23 am

Link, Leica website, incredible, they state it explicitly, astigmatism is left to be corrected in the eyepiece or tube lens
https://www.leica-microsystems.com/sc ... roscopy/

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Re: Leica 1750 Plan 10Ph/0.25 objective "repair"

#15 Post by hans » Sat Jul 31, 2021 7:53 pm

Oh yeah, I had forgotten about that Leica article. I was thinking the ATC 2000 came before the Delta/HC systems, at least newer HC stuff seems to usually be clearly marked "HC", but not really sure. There was some discussion of the progression in this older thread:
https://www.microbehunter.com/microscop ... f=5&t=8625

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Re: Leica 1750 Plan 10Ph/0.25 objective "repair"

#16 Post by patta » Sun Aug 01, 2021 6:54 am

hans wrote:
Sat Jul 31, 2021 7:53 pm
Oh yeah, I had forgotten about that Leica article. I was thinking the ATC 2000 came before the Delta/HC systems, at least newer HC stuff seems to usually be clearly marked "HC", but not really sure. There was some discussion of the progression in this older thread:
https://www.microbehunter.com/microscop ... f=5&t=8625
Wow, read it now, that was some historical thread

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