Steven Tribe
10-Dec-2012, 16:52
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
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