More adventures with Canada Balsam

[Steven Tribe]

Starting point for this was B&L Protar VII (the series that was made quite late into the 20th C) bought here a month ago.

This last lens is a double protar. Two matched 11 3/16 inch cells. Combined, they provide you with a lens of 6 ⅜ inch focal length. Perfect for 4x5. Pop off one element, and you have a slower 11 3/16 inch lens. The lens barrel is in decent shape, and the the iris works fine. One cell has balsam separation at the edges, so it is not perfect by any means. The glass, however, is in really good shape. Comes with the flange.

The protar is shown in the first image. There is separation. But, as I, and others, write on that auction site "this will have effect on imagining capabilities".

I couldn't resist having a go at re-doing the cement. The first shock was how well made these B&L protars are designed and engineered. The mushroom shaped lens has 4 pieces of glass and 3 cement layers and is held in position in the cell by a pefectly fitting "mushroom shaped" threaded brass retainer. I have never seen any thing like this build quality except in much larger lenses.

Soaking in Xylol revealed that the black edging enamel was completely resistant to this solvent. This was fortunate in that the 2 joins that were damaged soaked up the solvent gradually, whilst the OK join was protected by the unbroken black paint finishing. So it became a double balsam job rather than a triple.

I had the cheek to try and use the mounting cone as a means of holding the 1+2, 3 and 4 pieces during the setting stage after the glueing.
This appeared to work correctly, but I was unconvinced when trying to align reflections from a spot light. There are very violent curves on the component lens which would show the slightest of errors in misalignment.

Second attempt without the brass cone and using elastic bands was a complete failure. Sideways slip in two directions. Back to the xylol solvent once more.

Third attempt was to join 3 to 1+2. These are all exactly the same diameter. Worked well and was hardened for a few hours (to-day).
This was then placed in the cone mounting and the 4th (much large diameter) glued on top. The cone mount was screwed into the rest of the cell mount and warmed to harden the balsam. Worked.

So lessons learned are

- B&L made a awesome protar and found a fantastic sealing edge enamel.
- My guess is that this enamel protects the balsam. Usually when I compare the re-done cell with the original cell, I can see the slight discolouration of the old balsam. In this case, there is no difference between old and new.

Photo legend.
1 is as purchased
2 top is lens 4 - left is lens 3 - right is lens 1+2
3 is completed new cell with the old cell

[goamules]

Good job, you are becoming the expert at recementing antique lenses. I also think B&L had the best quality. I recently cleaned an 1890s Ziess patent B&L binocular, and it was built like ....well, like the precision tool it was. Zeiss allowed B&L to be a secondary manufacturer for a reason.

[Tim Deming]

Third attempt was to join 3 to 1+2. These are all exactly the same diameter. Worked well and was hardened for a few hours (to-day).
This was then placed in the cone mounting and the 4th (much large diameter) glued on top. The cone mount was screwed into the rest of the cell mount and warmed to harden the balsam. Worked.

Good Job Steven!

I once recemented a TR triple convertible element -- 5 pieces of glass. I essentially ended up using a method very similar to yours: cementing cells one by one in sequence, anything else led to a mess of balsam and poor alignment. I would not want to do this again, as it took a long time to get right. However, seeing your results, I'm tempted to go after a protor VII element with edge separation that's been bothering me for a while

cheers

Tim

[c.d.ewen]

How difficult was it to unscrew the retaining ring? The front glass is fairly high-crowned, and I'm wondering if it's necessary to make a special tool to get it out.

Was the 4 element glass easy to get out of the brass mount?

Charley

[Steven Tribe]

Very easy - just one screw thread. Both cells were opened with normal finger pressure
In the cell I repaired, the lens could be just eased out.
In doing the new photo, the old OK glass couldn't just be pushed out of the left hand side 1/2 cell with ordinary pressure. I imagine that the seeping balsam from the 3 joins over 4-11 decades has locked the lens in position.
A days soak in xylol should allow the lens assembly to be pushed out.

Better photo below. Although not visable, the internal section of the mount follows the changing diameter of the glass perfectly.
I think this is a later protar VII - so it is possible another cell mount technique was used for the early production.

[c.d.ewen]

Thanks for the picture, Steve. That explains it. I had not thought that the lens disassembled that way. I tried unscrewing the two cells. One will take some extra effort, but the other unscrewed easily. That lens wiggles very slightly in the mount, so I guess I'll make some kind of jig to center the elements. Wonder where my xylol is?

Charley

[Steven Tribe]

Another tip from recent experience.

Zylol/zylene works very well - but requires quite a lot of patience. I have also tried Acetone, with the same kind of speed, but as acetone evaporates very quickly, cleaning up the deposits on the surfaces is more difficult.
I have had problems with a Dallmeyer 3B achromat using Zylene - only a few mms penetration after a week. So I decided to switch to acetone. This produced instant real progress - completion in 24 hours. The appearance is somewhat alarming, with white patches everywhere. But it cleans up completely.
Acetone is a solvent that you should avoid breathing and it will remove the surface oil from fingers instantly. So be careful.
There is no doubt that acetone is the right solvent for synthetic cement. It is possible that the lens I have been working with, had been (badly) recemented in the modern era when experimental synthetics ruled.