Fungus on antique Lens: Can it be fixed?

[Steven Tribe]

Sorry, but there is a good deal of hearsay and misleading (wrong!) information here already!
There are a number of lengthy thread on balsam replacement in the DIY section.

- Don’t use hot/boiling water. Heat transference is far too Quick and will stress the glass. Both cracking and Devitrification.
- Sterilisation is a waste of time. Fungus spores are everywhere - correct storage is the Way to go.
- Sounds like balsam breakdown, which can have tendril-like appearance. Long term zylol bath (up to 2/3 weeks) to separate.
- Many well known makers used turning down thin brass edges in a lathe to Mount glass, rather than screw mounts. A skilled machinist can open these up on a lathe -we can’t, but can do it with hand tools. Result can be a Little rough.
- Canada balsam is the same stuff that is used in microscope slide making.

[Drew Bedo]

It just keeps unscrewing...

Most likely your Darlot is of Petzval type
Attachment 205186



Attachment 205190

Thanks. However, this is not a Petzval design. The markings say
Hemispherique Rapod" which I understand to mean that it is of the Repid Rectilinear design. The front and rear cells donot seem to unscrew. I hesitate to jujst start prying on things with a thin knife blade. or on thing,its 250 to 170 years old and about anything is likely to fail from aqge alone. The second reason is that this is from a well known maker. if I was trying to salvage parts from a no-name unmarked partial assembled non-collectable lens I might feel different.

Anybody here know how to properly dismantle this lens?

[pgk]

If you intend to use the lens then try it out before doing anything else. I have been using old lenses with many optical faults including balsam separation, scratches, yellowing of the balsam and so on. Despite this they can produce surprisingly good results. I say can because the biggest problem is an increase in flare so I find it essential to use as much shielding as possible. I have just bought a Hasselblad Pro Shade from a dealer for the vast sum of £15 which I will modify and make front cutouts to match each lens I use it with. Ungainly perhaps but quite a cheap and hopefully effective solution to minimise flare and optimise contrast. Post 3807 here: https://www.largeformatphotography.i...amera!/page381 is taken on a 1860 lens with such flaws.

[pgk]

And just to illustrate this further, here is a shot taken on an 1859 lens (using a step and repeat digital back I am building on a Gandolfi) and then stitched and processed in Photoshop) which, whilst not perfect, is a reasonable enough image.

[Steven Tribe]

Thanks. However, this is not a Petzval design. The markings say
Hemispherique Rapod" which I understand to mean that it is of the Repid Rectilinear design. The front and rear cells donot seem to unscrew. I hesitate to jujst start prying on things with a thin knife blade. or on thing,its 250 to 170 years old and about anything is likely to fail from aqge alone. The second reason is that this is from a well known maker. if I was trying to salvage parts from a no-name unmarked partial assembled non-collectable lens I might feel different.

Anybody here know how to properly dismantle this lens?

The quoted article matches my experience.
Most RRs/aplanats do have these Quick mountings. They are not designed for servicing. Advances in Optics at the time (1890’s) meant most makers were expecting their products To be replaced within the decade. A knife edge is the only for an amateur without lathe experience.

The Hemispherique is very much a “run-of-mill” aplanat like many others. The name is just a bit fancier!
Darlot was a Company in difficulties when this was made, having made no contribution to photo optics since 1865!

[Drew Bedo]

[QUOTE=Steven Tribe;1558699]The quoted article matches my experience.
Most RRs/aplanats do have these Quick mountings. They are not designed for servicing. Advances in Optics at the time (1890’s) meant most makers were expecting their products To be replaced within the decade. A knife edge is the only for an amateur without lathe experience.

The Hemispherique is very much a “run-of-mill” aplanat like many others. The name is just a bit fancier!
Darlot was a Company in difficulties when this was made, having made no contribution to photo optics since 1865![/QUOTE

Thanks . . .all good to know. If I mess it up the loss will not be much felt in the field of antique lenses.

I still have an interest in attempting to deal with the fungus issue. Separating the elements and recementing later is a different problem to address later. First, the front cell has to come apart.

How can this front lens cell be disassembled?

[BrianShaw]

I’d consider it non-repairable. As Steven Tribe has said several times, there is a possibility of unrolling the brass lens holder, but if the brass has work hardened it will crack and break. I doubt there is a possibility of anealing the brass with the glass in place. Lathe or thin knife... doesn’t matter; same risk. Other approach would be to cut the retaining rim with a graver and remove the lens. A Gem-setting technique used for use in jewelry. But then you’d need to either raise a new edge to re-retain the lens or figure out some other alternative.

It might be better to use-as-is or relegate it to museum-pice status.

[Drew Bedo]

Thanks Everyone.

From the advice in several responses here, remediation looks less and less likely.

I want to do some additional learning though. I have doubts that this is an 1890s era item. I have read somewhere that the marking from 1860 through 1863 were "Darlot Paris" as engraved on this lens. Previously the marking would have been "Jamin Darlot" and before that, just Jamin. It might be worth remembering the "Rapid Rectilinear" is a term rendered in English, while "Hemispherique" is a term rendered in French, by a Frenchman. Later marks were different in details of address and so on I think. I am just learning these things, so any information is appreciated. I am open to being educated or schooled.

Perhaps I will spend some lens money on a reference book someday. Wikipedia does not have much on it.

[BrianShaw]

If it makes you feel any better, Drew, I have an old RR lens (not nearly as nice as yours) that has the aperture control lever (little knurled knob, it once was) snapped off. What’s worse... I remember snapping it off trying to loosen up the aperture. Can’t figure out how to repair and anyone I ask has no good suggestion. It’s useless to me as a lens but still looks great on the shelf.

[Nodda Duma]

Drew,

If the fungus is in the cemented surface then I can repair it if I can get the glass out. Burnished retainers suck..I know why manufacturers did that but that doesn’t make them nicer for it. It’s not period-correct, but I’ve turned burnished retainers down to remove the lens, effected the repair, and then rebuilt the burnishing with epoxy. If you want me to take a look send me a pm.


Take pgk’s advice up above first, tho.

-Jason