?? Fungus or Separation ??

[AgX]

To be fair to anyone, and to be careful in wording:
the artefact is anything but common and the diagnosis here reaches from fungus over seperation to being clueless.

 

[jjphoto]

Old-N-Feeble, I have a particular interest in Computar dL lenses and have researched and written about them quite a bit. I also have two copies of the 1.9/55 dL and both have separation (as do some other other Computar dL lenses that I have). They are NOT worth USD1800 however that doesn't mean someone wont pay that one day, you never know.

I strongly suspect your lens has separation (which can look quite different depending on the exact sample of the lens (one of my Computar dL 135mm lenses looked like yours)) but if you look at the rear block it is 'possible' that the lens has fungus but given this lenses history one would expect any fungus (if present at all) to be in addition to the almost certain separation which is pretty much a 'given' for this lens. The ONLY way this lens will NOT have separation is if it has already been repaired, which can be done and costs North of USD250. I'm considering having one of my lenses repaired too but my 'to-do' list is long and this is low on the list.

Optically these lenses do not perform terribly well if the separation is left so you really do need to get it fixed if you want to get the best out of it. I use my 1.9/55 dL's as a taking lens on Sony A7R2 and find it quite interesting to use, especially because you can adjust the render by altering the amount of spherical aberration correction.

Your copy appears to be in superb condition, really nice, aside from the separation of course.

By the way, the rear group unscrews easily from the body of the lens so you can inspect the two cemented elements more closely, which are towards the centre of the lens. This link shows lens construction http://photocornucopia.com/1073.html

A bit of general blurb on Computar dL lenses here: http://photocornucopia.com/1057.html

 

[Old-N-Feeble]

If it is separation, or if it's fungus but hasn't etched the glass, then it's worth repairing. I paid US$358 delivered because the seller accepted a low offer. If the glass is etched then I need to send it back.

 

[Patrick Robert James]

ONF, sorry your thread was taken over by a whacko. Lol. If you paid only $358 for it then it is worth fixing. If you want to verify the separation you just need to do what jjphoto suggested above and unscrew the rear group. If you want to venture into the lens, the cement that fails in all the Computars I have had (I have a 50, 65, 80, 105 and two 135s and everyone had separation) dissolves easily with acetone in about a day. You probably won't want to though if you've never been down that road before. You don't want to mess it up, although it isn't rocket science.

Feel free to pm me if you want. I am kind of done with this thread.....

 

[sissysphoto]

Old and Feeble. The other more knowledgeable poster on this particular lens has made a plausible point as to your problem. Undoubtedly separation has taken place. Were it not so, then how was the fungus able to get into the doublet? Certainly it would be very much more difficult for such entry if the elements had a good seal.You've bought the lens on a negotiated deal. It is yours now, I'm afraid. Please believe me when I tell you that separating the glass is something anybody can do. Don't throw good money after bad by sending it off. Remove the doublet from the lens assembly and place it in a little jar of methylene chloride with a cotton pad at the bottom to prevent scratching.. I say methylene chloride because you don't know if the cement is balsam sap or a much harder to dissolve synthethic glue, which acetone can't help. But given a month, even Meth Chl will separate the 2 glasses. Clean them with cotton pads soaked in the solvent to clean off residue, and reglue with balsam sap, easily available on the internet. Just a little pool in the middle and put the 2 together, chocked at 1/3's with wood blocks to center them up. After a week you can use more solvent to clean the glass surfaces and edges of excess hardened sap. The solvent won't hurt the lens coating so don't worry. You can use all the solvent and cotton pads you need. You can do this. Methylene Chloride comes with a California cancer warning, but so does everything. It is used for decaffienating coffee and a million other things. It's non flammable, and quite safe. It is VERY evaporative. Not like freon or butane, but still quick. GL

 

[Old-N-Feeble]

Thanks everyone. I'm going to do the repair myself.

 

[E. von Hoegh]

Are the white blotches with concentric rings fungus or separation?

That's one strange looking lens... I've never seen fungus show diffraction rings though, so it's likely separation. Really strange separation...

 

[E. von Hoegh]

Thanks everyone. I'm going to do the repair myself.

As someone pointed out, "it's not rocket science". (Actually it's not science at all but technology)

Here are my experiences, if they help at all.
It's good to determine what the lens was originally glued together with, up to WWII it was Canada Balsam, but experience during the war with aero cameras used at high altitude and undergoing huge & rapid temperature swings showed up balsam's weaknesses and various synthetic epoxy/polymer cements were developed; later on UV curing cements came along. I've used balsam to recement old Rapid Rectilinears, binocular & small telescope objectives and a couple eyepieces, an early Protar, etc. All were successful; however you must keep the elements precisely aligned until the balsam sets. The first lens I repaired this way, I used locally harvested balsam on two R-R doublets. They were "cured" on a surface plate kept at about 90f for ten days, alignment was maintained with machinist's V blocks. Lens works great, however I managed to get one tiny speck of whatever in the cement of one doublet. Watch out for dust!
I've used the UV curing stuff just once, "Norland NOA61" on the front doublet of a Leitz Summitar. be certain if you use the UV stuff that everything is aligned before you cure the cement - you can separate the elements if you have to but it can take weeks.
Mark the edges for rotational alignment before you separate the elements, I use a hard pencil. I'd use a carbide scribe but I'm afraid of chipping a flake off an edge of an element.
Good luck!

 

[cowanw]

Just in case, a fungus killing treatment may be in order after you separate the elements.

 

[Theo Sulphate]

O-N-F: good luck and keep us informed of your progress.

 

[Old-N-Feeble]

I'll let everyone know how it goes.