PDA

View Full Version : Balsam Breakdown on ML Petzval



Pete Watkins
28-Dec-2009, 02:19
Sorry about this if it seems a stupid question BUT I recently bought a large old magic lantern Petzval (for 20 UKP) and when I got it home I noticed that the front elements are suffering fron really bad balsam breakdown. I'm not blaming the seller, I should have looked harder. The daft question is if I can seperate the two elements at the front of the lens where the problem is, and if I can clean them up, why would they need to be glued together again to get the lens up and running. Why can't they just be put next to each other without the glue? And would it be hard to clean and re-glue the elements.
Sorry again,
Pete.

Steven Tribe
28-Dec-2009, 03:19
Pete, count yourself lucky! The worse problem with these lenses is missing and chipped rear lenses (heat damage). Canada balsam is now available in small handy quantities on that site. The sequences are pretty well described on-line. Separation, in my experience, takes a little longer than the authors say. It can be especialy long when the major part of the balsam has dried out and become opaque. I believe physical contact without oil or balsam was tried in the early days. But alignment and reinstalling in the lens cell would be a nightmare. Some front and rear lens cells were never meant to be dismantled. Instead of threads, the barrel was fitted with a small "lip" which was turned down over the glass in a lathe.

As you are in the UK I would recommend you try and get hold of "Lens-Work for Amateurs" By Henry Orford. This is a Pitman manual which was reprinted often in the 20th C - at least as late as 1953 (my copy). Over 200 pages of "how to do it" and figures. Not a rare book and certainly not sought after as some are.

Peter K
28-Dec-2009, 03:29
Why can't they just be put next to each other without the glue? And would it be hard to clean and re-glue the elements.
A cemented lens works as a one lens made from glass with special features. But without cement one gets three lenses, two made from glass and separated by a small air-lens.

You can find many hints about recementing lenses in this forum. A cheap and easy way is to use synthetic balsam from a microscopy supply house. Other as with uv-cured lens-cement it can easily resolved with benzene or xylol.

Steven Tribe
28-Dec-2009, 03:53
Readers. Please note that Benzene is C6H6 - the most simple aromatic hydrocarbon. Do not inhale or get it on your skin. A very good solvent, though!

Tom Keenan
28-Dec-2009, 09:24
Using the procedure in this link...
http://www.skgrimes.com/popsci/index.htm
I re-cemented an old rectilinear lens with excellent results. I got in some trouble with my wife for stinking up the kitchen and I relied on a friend to help in the choice of a proper UV cured cement.
Tom Keenan

Pete Watkins
28-Dec-2009, 10:48
Many thanks for your help lads.
Steven the book is on its way via Amazon. As the lens was not expensive I'm going to give re-cementing a go when I've seen the book and got the chemicals together.
Thanks again everybody,
Pete.

Frank R
28-Dec-2009, 13:38
Before you go re-cementing... try to gently re-heat the lens. The balsam will become fluid and get rid of the problem. You then remove it from the heat and let it cool.

Use a low heat, like 150 degrees, in an oven. Keep the elements in their ring to prevent movement. Place it in a pan and put it in the oven on the lowest setting. Watch it every few minutes. It will slowly warm and thin out; this may take 20 minutes or longer. When the glass is clear again, take it out and let it cool.

If you leave it in too long, the heat will cause the balsam to run out from between the elements.

This technique is free and easy. The worst case is you will have to re-cement your lens.

Steven Tribe
28-Dec-2009, 14:39
The breakdown is often associated with colour change, crystallisation and worse. I would think that after 100 years it would be a good idea for a change of balsam. My experience with UV modern glue was very good and the UV hardened quickly in sunlight. It is not cheap, however, and has a limited shelf life in the bottle (about a year). My next project (RR) will be with canada balsam. I wouldn't recommend reglueing 4 or 5 component lenses!

Orford's book is great fun! There isn't too much about balsaming - which he obviously considers an unskilled routine activity. But a lot about making lenses, aperture making, traditional brass objective construction, lacquers and blackening internal brass components.
usould

Tom Keenan
29-Dec-2009, 17:48
another handy resource

http://www.optical-cement.com/

Tom Keenan

Steven Tribe
30-Dec-2009, 02:52
Very interesting and obviously a good alternative to Edmonds (who have an excellent customer service in my experience). I checked the shelf lives of the more interesting products and still found them to be only 12 - 18 months. I have recementing as a winter activity and use just a few drops every year for each lens I tackle. So with a synthetic glue I would have to buy a new tiny bottle every year and dispose of last years bottle (still almost full) in an environmentally friendly way.