Burnished lens mounting

[swmcl]

Hi,

Could I be given a good explanation of the situation where a lens is 'burnished' into the frame ? How is this done ? Can it be un-done ? At what risk ? By whom ?

I have a Xenar lens that does have a front lens ring with a couple of notches but was told that it had a burnished lens mount when I tried to get it cleaned.

The lens was then returned to me but I want it cleaned. So I now ask the community for advice and help.

Should I purchase a lens spanner from MicroTools and proceed as far as I can myself ? I must admit that I do tend to go this way because I think others aren't as interested as going the distance as I am.

I'd be interested in your thoughts,

Rgds,

Steve

[Arne Croell]

A burnished lens mount means that a thin lip of the lens cell or barrel is crimped over the lens edge by mechanical force. No retaining ring is involved. If your lens has a burnished mount, the ring that you see is there for decorative or other purposes.

It is pretty much a non-reversible mounting. To get the lens out, you would need te bend the thin metal "lip" over the glass back up, and then fold it back to its original position when you put the lens back in. In most cases, the metal will not withstand this multiple bending and break.

[swmcl]

Thanks Arne,

Is it a common practice to do this? Going by what you've said it means the lens can never be fully cleaned. This is a rather interesting manufacturing decision!

I wonder too if there is a manufacturer or period of lens making when this has occurred.

Now I'm a bit frustrated

Rgds,

[imagedowser]

When I got my Dallmeyer No. 3, the rear lens was out and and the bezel that held it in was turned up. Apparently, someone took the lens apart. Having studied jewelry making, it was fairly simple to remount the lens by re-rolling the bezel with the lens in place. There was an article on lens re-cementing on this site that talked abt the fragile nature of thin brass bezels and the poss of fracture. You might check it out. The guy to talk to is: dag camera repair.com, or S.K.Grimes. Good repair isn't always inexpensive but you get what you pay for... Good Luck, Bill

[imagedowser]

.......also, John, at Focal Point.

[GPS]

Hi,

Could I be given a good explanation of the situation where a lens is 'burnished' into the frame ? How is this done ? Can it be un-done ? At what risk ? By whom ?

...

Steve

There are several methods of burnishing the lens (a press or a special turning device is used). The joint is regarded as non reversible. It is used for rather smaller lenses or as a cheaper way of lens assembly. I don't think that a repair centre would take the lens for cleaning as the risk of breaking it is considerable.

[Steven Tribe]

The bending of the thin lip over the mounted lens in the brass is (was!) done by mounting the lens assembly in soft jaws in a lathe and applying a "pusher" - piece of hard wood to slow push the thin brass to make a sealing contact. The system was used on all sorts and sizes of objectives. In the first decades of the photographic revolution it was expected that their objectives would only be in use for a few years so thoughts about cleaning and repair were not foremost!

Lifting the edge can be done professionally in a lathe with a similar set-up - but I doubt whether anyone has experience and soft jaws (box wood) these days. I have opened 4 of this seals without damage. The problem is to get the first small first gap. I have found that a very solid hobby knife is the way to do it. This is, of course, a considerable health hazard! Moving a flat thin edge slowly around the circumference will create a gap without damage to the lens surface. This gap can be widened in steps by inserting non metallic flat feelers. You will not be able to avoid a degree of cosmetic damage to the brass edge. Brass will be able to stand up to this treatment without becoming brittle. Remember that the lens may be stuck with excess balsam which has been leaked. Remember too that the hidden edges of the lens may be complex as not all the components may have the same diameter.

Resealing is a quite easy process. Just imitate a lathe's movement on the brass and apply pressure with a solid hard wood edge.

[GPS]

Steve, I gather that you are speaking about old lenses, which is not the case of OP's Xenar. The problem with resealing the lens is more complex as a more modern lens needs to be centred while burnished. The correct tool for that (if you want to use a lathe) is a 3 parts instrument moved while the lens is held centred. Also, the greatest danger in removing the edge is not to damage the brass but the lens itself.

[Steven Tribe]

Yes GPS, my experience is with pre-1900 objectives. I totally agree with you about the need for some helping mechanism to keep the glass central if it is not an exact fit in the recess. I suppose one could introduce some sort of packing material between the glass edge and brass "hole" to ensure the lens was held in the exact centre of the mount.

There is a wonderful book by Henry Orford called "Lens work for Amateurs" which shows all the processes involved in making an objective.

[Glenn Thoreson]

Many lenses were made with a removable ring on the front and the spun mount on the rear. If your front ring has spanner slots AND threads aroung the inside of the front of the barrel, it can be, at least, disassembled enough to clean the dust out. The rear cell in a spun mount was usually a cemented doublet, and usually it is not necessary to remove it from the mount if the front group will come out. Those rolled over spun mounts were someone's idea of a joke, methinks, and a bad one at that. Good luck.