Xenotar lens separation?

campy51

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How common is lens separation in the Rolleiflex Xenotar lenses? I know the Planar is common but never heard of the Xenotar having this problem.
 

Besk

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The elements that are cemented together in the Xenotar lens are flat where the elements of the Planar are curved. Slight differential thermal expansion between glasses of two different indexes of refraction would put more stress on two curved surfaces cemented together compared to two flat ones cemented together. That is my opinion.
 

gone

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I had a Rolleiflex w/ a Xenotar w/ pretty bad coating issues. This is something to look for on these lenses. However, even w/ the coating issues, that Xenotar was the sharpest lens I had. The Planar is great for sharpness corner to corner even wide open, but the Xenotar lenses are probably sharper.

Here's what that looks like. It can often be confused w/ separation if it gets too far gone.

https://www.flickr.com/photos/marlforl-werlforl/5191396547/
 
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Nodda Duma

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I’ve repaired 3 or 4 Xenotars with lens separation over the past year.
 

NB23

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It is much rarer than from Planars. Especially the tele-rolleiflex which are 100% inflicted or will be in the future.

the xenotar’s glued lenses are the rear ones as opposed to planar’s front.
 

Nodda Duma

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Yes I’ve been repairing balsam separation and coatings on the side of my side business, but have not advertised it widely or I would get swamped. Last job was a 16 1/2” focal length Dagor (both sides) and a Planar taking lens before that. That Planar had a flat bond surface too btw. Right now I’m working on a couple of lenses with bad coatings that I will strip off and send to one of the optical shops I do business with to have recoated.

Here are some pics I grabbed off my phone on recent jobs that I share with the owners, since it takes a few weeks to separate the elements not to mention working it into my schedule. Many of the owners are here on photrio or the large format photog group.








 

Dan Daniel

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I have a Rolleiflex 2.8E with a Planar that was recently recemented and recoatd by Nodda Duma (J. Ho, Nodda). Looks great. I suggest everyone be careful here- don't want to kill the optical tech who lays the golden lenses by overwhelming him!
 

Nodda Duma

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Here’s the lens I’m currently working on. Rear doublet of a Zeiss 165 f/2.8 Zeiss Tessar. It need the AR coating stripped, some surface haze polished out, and recoated. I repolished the surface this evening and will send out to the shop I use to put a modern single-layer coating on. Same coating performance as original, but more durable.

 

Dan Daniel

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Gotta admit, that photo looks like an archeological study of an unknown religious alterpiece.....
 

wkh

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Hi, Just acquired a Rolleiflex 2.8C with the Xenotar lens. The viewing lens is perfect, but the taking lens has a lot of wear on the front coating and there are two weird "flower" shape defects right in the middle of the lens (see attached photos). I hope that these were just fugus which I could clean up after I disassemble the front lens group. However, I fear that they may be point seperation of the cemented second lens group. If that is the case, could someone re-cement and recoat the lens for me? The 2.8C was too good to bin so would like to put it back to use. Cheers! WK
 

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JPD

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That looks like separation to me, and I agree that the lens looks to be a good candidate for recementing and recoating.
 

wkh

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Many thanks for all your replies and links for the potential solution providers.

I have remove the front lens group and will disassemble it this week to confirm the source of the defects. I have managed to recement the back lens group of a Carl Zeiss Jena 50mm f4 before so am a bit tempted to give it a go myself. However, the CZJ was a junk lens to start with and the Xenotar is far more valuable so not sure it is worth the risk. In any case the front lens will need to be polished and recoated anyway.

I am originally from Taiwan and my parents are there right now, so the optical repair service there is somewhat attractive. However, he seems to only polish without recoating the lens. Furthermore, I don't want to risk the lens got damaged or lost in the post.

Therefore, the German optical services are preferred unless they are way too expensive. Does anyone who know someone based in Austria (or perhaps in Hungary or the Baltic nations) who may be capable to help?

Cheers!
 

JPD

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wkh said:
Therefore, the German optical services are preferred unless they are way too expensive. Does anyone who know someone based in Austria (or perhaps in Hungary or the Baltic nations) who may be capable to help?
Click to expand...

It's very difficult to find a service like https://optik-labor.com/ that can do all the needed work, polishing, coating and cementing. I think that in your case, the front element needs polishing and re-coating, and one lens group that needs re-cementing, so send them an email and ask for a rough estimate.
 

wkh

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Thanks JPD. I will check with them once I confirm the condition of the lens.

I wonder Nodda Duma is still repairing lens…
 

wkh

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I have taken the front group apart last weekend and confirm the defects (1st lens coating wear and two point balsam separation in the 2nd/3rd doublet).

I have emailed Foto Olbrich in Germany based on the recommendation of other Photrio members and they referred me to Dr. Prenzel in Optik Labor instead but with some stark warning regarding the risk of lens cracking during re-cementing and recoating.

Personally, I think the lens cracking warning is a bit overstated. The most dangerous part is probably heating up the doublet to separate the glasses. However, I believe that due to the flat gluing surface of the Xenotar lens the differential expansion stress should be minimal. There is of course risk of stress cracking during polishing, but I would assume any optical technician with reasonable skill would know to avoid that. However, it would be good to hear from someone who actually have it done before to see whether my assumptions are reasonable.

The other forum member has suggested someone from the Arsenal factory in Kiev as a possible place where I could have the lens re-cement and recoated. It is of course riskier to send the lens to Ukraine now there is a war going on, but I will try to contact them this week to see what thy say...
 

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Nodda Duma

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wkh said:
Thanks JPD. I will check with them once I confirm the condition of the lens.

I wonder Nodda Duma is still repairing lens…
Click to expand...

I still repair separation. Just haven't been on Photrio lately. I am no longer able to strip and recoat, however. All that stuff is still packed up after moving.

Thing about using heat is that doublets separate specifically because the coefficient of thermal expansion of the crown and flint have a very significant mismatch. Flat bonding surfaces do not reduce the stress induced with heating, and I have seen the soft glass that flints are made of flake like an arrowhead with heat. It is always a risk. Much less risk using a solvent to separate.

p.s. soaking in a 10% sodium chloride (table salt) solution for several days and then wiping clean will remove those old MgF2 coatings if you want to eliminate that damage.
 

wkh

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Thanks for the reply and glad that you are still active, Nodda Duma.

I assume the 10% soldium choride will only strip the front coating, hence minimize/remove the hairline scratches. That will not fix the doublet separation, right?
 

wkh

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NaCl + MgF2 = NaF + MgCl2​

I assume that, if the doublet is glued together using Canada balsam, I could use xylene to separate them, right?

I have separated and re-glued the back triplet in a CZJ Flextogon 50mm f4 lens before. I actually placed it on a halogen light bulb for a few minutes and, to my surprise, it came right apart. Wiped off the residues with alcohol and glued them back together in a homemade rig using water-based microscope slide mounting medium. The re-assembled lens looks alright but I of course cannot guarantee its optical performance. However, it was a junk lens to start up with so I have nothing to lose. The Xenotar is a completely different story...
 
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