View Full Version : edge separation of protar convertable

30-Apr-2008, 06:34
i got a protar convertable lens, and it has some edge separation on the front and back side of the lens. is there anyway i can clean this? or do you guys know any place that service the edge separation?


Kevin Crisp
30-Apr-2008, 07:25
Sean: Each element, front and back, is made up of 4 pieces of glass. They were originally glued together into one element by a tree-derived clear sap like product called Canadian Balsam. When you separate one in the oven the scent is really something. It fills the house. The stuff was clear, melted at high heat, and apparently holds up for a good many years. Some of my protars are 100 years old and have no separation. (Actually a lot of the older ones seem to hold up better than ones made 30 or 40 years later, for whatever reason.) And then sometimes it starts to crystallize, and an amber/brown ring around the edges shows you how far it has progressed. There is nothing to clean -- I wish it were that easy. What has failed is a thin layer of glue in between pieces of glass.

I can't be really specific without seeing your lens and the focal length and diameter, but as a general proposition, a ring of say 3 to 4 mm around the edge or on one side is nothing to worry about. You won't be shooting the combined lens at f:6.3 or f:7.7, and the single elements are pretty bad at f:12. So you will be stopped down to at least 16 in all likelihood on the combined lens and f:32 on the single elements. When you do this, the separation at the edge makes no difference except as to resale value where it can really drive the price down. (By the way when you use the single elements, refocus after you stop down to adjust for focus shift. Otherwise, like so many people, you will conclude that the single elements don't work well.)

If the separation is really bad, it can be repaired. Focal Point in Colorado does a great job and so does Balham Ltd. in England. Focal Point might be a little more expensive, but with the decline of the dollar I wouldn't bet on that. The turn around time from Balham can be pretty long compared to Focal Point, though the end product is very nice. Having a repair like this done is expensive, since it is a lot of work. Just getting the glass successfully apart without breaking it, and then getting it absolutely clean is many hours. Think $250 to $300, about as much as you probably paid for the lens. There is a risk of destruction to the lens if something goes wrong in the separation process, but this is rare. If you want to be completely crazy either of those firms can also coat the lens. This is not necessary in my opinion, but I have had both Focal Point and Balham recoat lenses and they look like new when I get them back.

This can be a DIY repair. I've done about 12 of the protars and a couple Wollensaks and I've pretty much got the hang of it. I've not broken one separating it. I am sure a professional repair facility would be horrified at my amateurish technique but the end result looks good and, more importantly, works for taking pictures. If your time is worth anything, then sending it out is cheaper. The ones where the elements are not all the same diameter are a lot tougher to center if you do this yourself. An amateur mechanically centers the individual lenses before gluing, the professionals have more sophisticated ways of doing it, as you can see from the S. K. Grimes tutorial. (If you want some idea of what is involved, go to the S.K. Grimes website, he has lots of information on doing it and a link to an ancient magazine article on this.) I'm not wild about the way the Grimes site showed how to separate the lenses, but it must have worked well for Steve and he did a great job for me on several I sent him. Unfortunately, Steve apparently didn't fully pass this skill on before his death and his company will refer you to Focal Point for this kind of repair if you inquire today.

You will probably glue and re-glue the first one you try if you do it yourself, there is a decent learning curve on this. If you let the new cement fully cure and then realize you made a mistake, the separation process for the modern cements is much more complicated. If you want to post a picture, odds are I'll tell you not to worry about it. I have been using protars of various ages for about 15 years and I have yet to have one progress and get worse while I've owned it. I live in So. California so I probably heat stress my lenses more than most.

John Z.
30-Apr-2008, 08:32
Kevin, you seem like you have really done a lot of tinkering with lenses! I just sent my first lens off to focal point for a recoat, and am anxiously awaiting the result (surprised that it takes about two months). Have you ever tried coating lenses as well? Just curious to see what would be involved for a do it your selfer.

Kevin Crisp
30-Apr-2008, 09:06
I had Focal Point polish and recoat a commercial Ektar. It came out like new, you should be very happy with it.

I think you have to separate all the elements to recoat, to prevent damage, then it involves a vacuum and the depositing of magnesium fluoride on the glass. I don't think my DIY efforts are going to go that far.

For a lot of classic lenses, like protars, I don't think coating makes a significant difference due to their construction. A single 19" element like Weston was fond of has two air/glass surfaces, front and back. I think coating is going to make no detectable difference in the images, and when testing a Balham coated one against an uncoated one the improvement was not noticeable. For a complex lens like the first plasmats I bet it works wonders, though.

John Schneider
30-Apr-2008, 09:14
Coating a lens is a different animal altogether. You'll need a chemical vapor deposition (CVD) machine, to begin with. These are used in the semiconductor industry to produce thin films, in addition to making optical coatings. Then you need a high-purity sample of magnesium fluoride. Thoroughly clean the elements, place them in a fixture in the CVD machine, pull a vacuum, and turn it on at the right temperature and right current, and leave it on for the right time to produce a thickness 1/2 (this may have to be 1/4; I've forgotten) the wavelength of (typically) green light.

if you're a researcher in semiconductor fab, thin films, or something that is produced by CVD (e.g., carbon nanotubes), then you may have all the equipment to try this yourself. Otherwise you may want to research the leaching technique used by the British in the early WWII time frame before they discovered MgF2 coatings.

Kevin Crisp
30-Apr-2008, 09:29
I knew there was a reason I hadn't looked into this further.

Glenn Thoreson
30-Apr-2008, 15:35
I've recemented a couple of aplanats and Rapid Rectilinears. I wouldn't try anything more complicated. ! Do this at YOUR OWN RISK ! I make a match mark on the edge with a little diamond bit, then I just put the glass in a jar of laquer thinner for several days. When it's ready to separate, it will slide apart on it's own when you swish it around. After a very careful cleaning, I put a drop of UV cure lens cement in the middle of the concave side of the front most glass. Lining up the match marks, I put the rear glass on top of the drop of cement and apply light pressure. It will creep outward to fill the entire area of the lens. Extreme care must be taken to not rotate the glass during this next step: Then, I place it under a 25 watt UV bulb for a couple of minutes. Done! If you try this, you have to be absolutely sure the cement doesn't get accidentally exposed to a UV source before you're ready. Sunlight is OK if you're in the shade and you work fast. Not for the faint of heart! Glue is available from Edmund Optics. It's amazing how beautiful and water clear some of these old things come out.