Disassembling a Leica HC Plan Fluotar 20X/0.5 NA lens and fixing crud advice needed

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C_Skinner
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Disassembling a Leica HC Plan Fluotar 20X/0.5 NA lens and fixing crud advice needed

#1 Post by C_Skinner » Thu Apr 01, 2021 8:01 pm

Hi All,

I have a Leica HC Plan Fluotar 20X/0.5 NA lens (part number 506503) and the front optics appear to be either cracked (very bad), the optical cement is separating (moderately bad) or some sort of schmoo has crystalized inside (Oh lordy! but possibly fixable). The image below is of the front lens taken with an inspection microscope when I use diffuse back lighting through the lens.

Image

I showed this image to a repair shop and they thought it was/is a goner. I thought well, if that is the case then I don’t really have much to lose so I started disassembling the lens and have hit a bit of a roadblock. As you can see I have successfully removed the majority of elements (all carefully marked) but I think I am now at the point where I need to remove the front lens and meniscus lens (I don’t know if this is the correct terminology, I’m a chemist). This assembly doesn't seem to want to slide down the lens barrel (yellow arrow) as the other elements did. It may be threaded onto the barrel, possibly glued, I'm not sure. Should I (try to) remove the outer hoodely-goober (sorry for the techno-speak, see red arrow) to gain access to the nosepiece (green arrow). Does the nose piece (that actually holds the front lens) piece unscrew? From the cutaway diagrams I have found for other similar lenses it would seem that they should come out as an assembly but, I have no clear idea how.
More importantly, what I'm going to do once they are out? I am hoping and praying that I can access the space between the lenses and blow out the mystery material but, any and all suggestions are welcome.

And yes, this does seem like a bad idea for someone who doesn't really know what they are doing but, I use this objective as a light collection optic in a fluorescence detector so traditional imaging quality isn't paramount just NA and low fluorescence.

Thanks in advance!

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dtsh
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Re: Disassembling a Leica HC Plan Fluotar 20X/0.5 NA lens and fixing crud advice needed

#2 Post by dtsh » Thu Apr 01, 2021 9:00 pm

I do love a good disassembly!

That is the weirdest "break" I've ever seen. I am inclined to think it might be a cement issue. Hopefully it's not one of the UV curing adhesives.

PeteM
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Re: Disassembling a Leica HC Plan Fluotar 20X/0.5 NA lens and fixing crud advice needed

#3 Post by PeteM » Fri Apr 02, 2021 1:16 am

It looks like a goner to me as well.

But in the interest of exploration, a couple thoughts.

First is that to get into most of the Leica infinity objectives, you need to remove the shroud covering the nose of the objective. This sometimes screws on. Sometimes affixed with cement. A Leica repair tech could tell you better. I'd start with a bit of heat and soft jaw wrenches and try to get the shroud off.

Let us know what works in your case.

Then you may find some covered holes with set screws buried below. These may hold the last few elements centered and in place.

When all is apart, I suspect you'll find a chipped lens surface.

BramHuntingNematodes
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Re: Disassembling a Leica HC Plan Fluotar 20X/0.5 NA lens and fixing crud advice needed

#4 Post by BramHuntingNematodes » Fri Apr 02, 2021 2:32 am

Yeah seems like I saw some similar-looking conchoids on a chipped and broken Zeiss lens just a little while ago...
1942 Bausch and Lomb Series T Dynoptic, Custom Illumination

Greg Howald
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Re: Disassembling a Leica HC Plan Fluotar 20X/0.5 NA lens and fixing crud advice needed

#5 Post by Greg Howald » Fri Apr 02, 2021 4:36 am

Looking at the image with the yellow arrow. Right where the arrow is pointing (having enlarged the image), that looks like a gap between the ends of a snap ring. Using a needle on the edge of that gap, pry the metal slightly toward the center of the lens housing and see if it moves slightly. If so it is indeed a spring snap ring that must be removed to complete disassembly. But remember that you are in a delicate and dangerous area. Don't let the needle or very small jewellers screwdriver scratch the lens cause then it's all over no matter what other success you might have. I have never seen a snap ring in that area but I wouldn't rule it out due to what I see.
I had a similar situation earlier in the year when I thought the lens was chipped and it was not.
Good luck.
Greg

Greg Howald
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Re: Disassembling a Leica HC Plan Fluotar 20X/0.5 NA lens and fixing crud advice needed

#6 Post by Greg Howald » Fri Apr 02, 2021 4:40 am

Looking at it a second time that certainly looks like a snap ring. The gap is right and so is the shape.
Greg

C_Skinner
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Re: Disassembling a Leica HC Plan Fluotar 20X/0.5 NA lens and fixing crud advice needed

#7 Post by C_Skinner » Fri Apr 02, 2021 1:14 pm

Hi Greg,
Thanks for the suggestion. I don't have the lens here at home but, I looked at that lens assembly carefully and I don't recall anything like a snap ring. The inside might be threaded but, if I recall, there are only one or two threads showing and I couldn't get a good angle to see it clearly. I went to look at the original quality photo and I think the gap you're seeing is just discolouration on the rim of the brass lens holder/assembly. The back end of that assembly looks pretty much identical to the other lens assemblies that have already been removed. I tried applying some force to the side to see if it would shift but it was in there solid. One other element was reluctant to come out as it had been glued into the barrel but, a bit of side-to-side force allowed it to wiggle around enough to slide free of the glue/lock-tight.

I don't know if this link will work but here are the original quality images. It's a little clearer.

https://photos.app.goo.gl/cofbdbRCnw9ecu648

Thanks again!

Greg Howald
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Re: Disassembling a Leica HC Plan Fluotar 20X/0.5 NA lens and fixing crud advice needed

#8 Post by Greg Howald » Fri Apr 02, 2021 1:52 pm

Ok. That photo is better! Thanks. Greg

tpruuden
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Re: Disassembling a Leica HC Plan Fluotar 20X/0.5 NA lens and fixing crud advice needed

#9 Post by tpruuden » Sun Dec 05, 2021 2:09 am

Did you succeed with the objective disassembly? I would like to know also, how Leica objective front end is put together - there is one with iris to re-lubricate here.

wabutter
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Re: Disassembling a Leica HC Plan Fluotar 20X/0.5 NA lens and fixing crud advice needed

#10 Post by wabutter » Mon Dec 06, 2021 5:53 am

I hate to be a downer, But I have been in the Wetzlar (where Leica is located) optics manufacturing area and a have seen first hand the process for assembly of objectives. I can tell you that the fixtures, interferometric tools and expertise in understanding the process will likely not be met with success by the lay person with out knowledge of how to use these tools and what the specifications are. At the best. you may find out the root cause of the failure, but the ability of to reconstruct and rebuild the objective is highly unlikely.

apochronaut
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Re: Disassembling a Leica HC Plan Fluotar 20X/0.5 NA lens and fixing crud advice needed

#11 Post by apochronaut » Mon Dec 06, 2021 1:48 pm

I would agree with that despite having successfully repaired dozens of objectives. The limit of my objective repair capability is cleaning, removing immersion oil, recementing lenses into their undamaged cells, lubricating collars and occasionally making one good objective out of two bad ones. The latter is fraught with alignment discrepancies but can be successful at times.

Re-cementing doublets or triplets is almost completely off the table and replacing one fractured lens element in a doublet or triplet nigh impossible.
The question also becomes : How easy is it to replace this objective rather than repair it? Most achromats or planachromats can be replaced pretty cheaply, certainly cheaper than spending a minimum of 3 but more likely 4-5 hours to repair it unless you are skilled and have lots hours of free time.
If it is a fluorite or apochromat type, then the time begins to make sense. I have a Reichert 100X 1.32 planapo with iris sitting here with a cracked front lens. A damaged or oil fouled front lens is about the easiest repair, unless the bezel is dented but then many objectives are designed with a separable front lens housing, allowing for an easy swap of just that element and little or no alignment or air space adjustment.
It was a rational response to the fact that over 90% of oil immersion objective failures are either a damaged front element or oil invasion. Having the ability to easily remove the front lens cell for either cleaning or replacement makes that particular $6,000.00 objective that much more worth the investment.

C_Skinner
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Re: Disassembling a Leica HC Plan Fluotar 20X/0.5 NA lens and fixing crud advice needed

#12 Post by C_Skinner » Thu Dec 16, 2021 4:53 pm

Hi All,

Didn't mean to ghost you all but it is the end of term and I'm up to my backside in exams and reports to grade. The posting asking for an update a while ago triggered the "Hmmm... that's right, I never did get that thing apart" memory. Well I re-examined the objective and resigned myself to the reality that it is/was a goner. So I thought, well nothing to lose here, might as well learn something. The issue was I couldn't remove (and I don't know the correct technical name for it) the piece that actually holds the first lens itself. It seemed to be locked/glued into the brass "barrel" that allows the lens assembly to slide back/forth when someone crashes the objective. I eventually tried using (close your eyes) vice-grips etc. all to no avail. Luckily, I run a chemistry lab and have "other" means to unlock the reluctant. A week-long soak in DMSO did the trick and was able to complete the disassembly of the objective. I don't recommend DMSO if you have a similar issue - I think it might also attack the anti-reflection coatings. Below is a revised link to all of the photos I have of the objective. For those of you who have one disassembled and don't know what your doing you can see the full stack of elements in their relative assembly order. The final two images show the sub-lenses in sequence but with "face" side up and "face" side down. The image with all of them sitting on edge (on paper clips) is the correct order and orientation if you are looking at a pile of lenses and don't remember the assembly order. The piece that was giving me grief is the stainless steel lens holder (third part in from the right) in the full stack image and on the piece of brownish paper towel. I think, but could easily be wrong, that the green remnants of what looks like a gasket is in fact epoxy that is used to glue the two parts (brass barrel + stainless steel lens holder) together into a unit.
The DMSO also did a number on the cement holding the first lens in place and I was able to extract it. As you can see, it is fatally damaged so I will be giving it a decent Christian burial later this week.

https://photos.app.goo.gl/cofbdbRCnw9ecu648

Thank all of you for your suggestions and thoughts on the objective.
Cameron.

Hobbyst46
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Re: Disassembling a Leica HC Plan Fluotar 20X/0.5 NA lens and fixing crud advice needed

#13 Post by Hobbyst46 » Thu Dec 16, 2021 6:05 pm

Wow. Was DMSO the first option, or did you try other solvents that failed ? like acetone, toluene/xylene, chloroform ?

C_Skinner
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Re: Disassembling a Leica HC Plan Fluotar 20X/0.5 NA lens and fixing crud advice needed

#14 Post by C_Skinner » Thu Dec 16, 2021 6:30 pm

I went straight to the BIG GUNS... no messing around since I know the optic was a goner. Not a good suggestion for those of you who want to recover the optics in a usable form...

PeteM
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Re: Disassembling a Leica HC Plan Fluotar 20X/0.5 NA lens and fixing crud advice needed

#15 Post by PeteM » Thu Dec 16, 2021 8:09 pm

Thanks for closing the loop on this.

tpruuden
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Re: Disassembling a Leica HC Plan Fluotar 20X/0.5 NA lens and fixing crud advice needed

#16 Post by tpruuden » Mon Jan 31, 2022 1:29 am

It may sound bit grandiose but interferometer and software for analysis is a quite cheap tool nowadays and optical fixtures are not that unreachable devices. Even if original cost effective mass-manufacturing requires relatively high complexity machinery, there is nothing inherently complicated in objectives, that would not allow anyone to reach the same or even better alignment, measurement and quality standards; given enough will and persistence.

I would highly suggest to look into this group posts: https://groups.io/g/Interferometry
wabutter wrote:
Mon Dec 06, 2021 5:53 am
I hate to be a downer, But I have been in the Wetzlar (where Leica is located) optics manufacturing area and a have seen first hand the process for assembly of objectives. I can tell you that the fixtures, interferometric tools and expertise in understanding the process will likely not be met with success by the lay person with out knowledge of how to use these tools and what the specifications are. At the best. you may find out the root cause of the failure, but the ability of to reconstruct and rebuild the objective is highly unlikely.

apochronaut
Posts: 6269
Joined: Fri May 15, 2015 12:15 am

Re: Disassembling a Leica HC Plan Fluotar 20X/0.5 NA lens and fixing crud advice needed

#17 Post by apochronaut » Mon Jan 31, 2022 11:58 am

I thought taking objectives apart in the first place WAS interfere-ometry!

tpruuden
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Re: Disassembling a Leica HC Plan Fluotar 20X/0.5 NA lens and fixing crud advice needed

#18 Post by tpruuden » Tue Feb 01, 2022 10:47 am

Well, it always starts as interfere-ometry and in the progress of developed pathology sometimes transits to full blown interferometry.
apochronaut wrote:
Mon Jan 31, 2022 11:58 am
I thought taking objectives apart in the first place WAS interfere-ometry!

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