Am I crazy to try this?greenspun.com : LUSENET : Large format photography : One Thread
I recently picked up a cheap Sinar F2 in great shape that had three lenses thrown in - a 210 Caltar S-II (near mint), 135 Sironar f/5.6 (separation in both doublets) and, the lens of most interest right now... Schneider 90 f/8 Super Angulon (an older lens, balsam used for cement, I think. A different lens formula from the more current one I have - totally different formula). Here's the question -
All of the black paint had chipped off of the cemented pairs front and rear. I emailed Steve Grimes and he kindly responded with a quote to fix both lenses but, considering the fact that they are duplicates of what I have already I opted to play with them myself. I stripped the paint from the rear pair and almost immediately saw edge separation begin. I figured this lens would have been cemented with a more modern material but from the speed of separation my guess it was balsam. Once it became apparent that this would be an additional repair I went ahead and dunked the doublet into liquid paint thinner and the next morning the task of separating the elements and cleaning them up was finished - now ingenuity is needed - and advice/suggestions.
I plan to recement the elements myself but have yet to finalize a plan on how to either mechanically or optically center them. So far it seems the best mechaincal approach would be to use a square Sinar filter to extend the plane of the elements by placing the filter on the flat surfaces and carefully measuring the distance off of my workbench until all four corners are the same height. I would do this for the larger piece (resting in a hard rubber 'O' ring to keep it in place once leveled) and again once the smaller element is dropped into the new puddle of cement. The filter would rest on the very back of the small element and again, I could measure the corner's distance from the table and make adjustments until they all match. I might even rig a stand that has adjustable height screws that could serve to pre-arrange the alignment prior to cementing and serve as support as curing takes place (at room temperature for the precure).
Sound feasible? Or am I crazy for taking this on? Anyone here tried this before? Should I try something with a laser pointer?
Thanks for any and all ideas.
-- Jim Roof (firstname.lastname@example.org), February 27, 2002
But you've got this far so . . . . >>>>>>>>>>>
-- Steve Feldman (email@example.com), February 27, 2002.
Not that hard to do, and Mr. Grimes has info on how to go about it at his site. I've used the mechanical approach. Call a machine tool supplier like Travers Tool Co (NY), MSC, or whomever and order yourself a couple cheap machinists v-blocks. Use these on a flat surface to center the elements- stand the v-blocks on end and push them together to capture the elements. I've used the UV cure adhesive by Norland (#61?) and you can get that from Edmund. It cures slowly under a quartz halogen lamp if you don't have a true UV source. Email me if you have questions.
-- Conrad Hoffman (firstname.lastname@example.org), February 27, 2002.
One more thing I have noticed and maybe someone else has seen it before. The area just around the cemented joint on the Super Angulon looks pretty roughed up. The optical path is pristine, not a scratch. But the areas that are 'frosted' near the cement joint look like they have been chipped dozens of times. Again, these marks do not extend into the polished surface but they do make for some ugliness when viewing the lens from a cosmetic standpoint and could be an issue if the lens was ever shot anything less than 2 stops closed. Is there a way to carefully dull these little chipped spots or is this normal for earlier Schneiders?
-- Jim Roof (email@example.com), February 27, 2002.
How good was the resolution of the lens after you recemented using the mechanical centering method? I'm thinking about using this same method on an old rolleiflex TLR I have.
-- edward kang (firstname.lastname@example.org), March 01, 2002.
The problem is getting the elements truly centered. Even a small deviation will result in poor optical performance at wide apertures. My advice is to let a local optical shop do the centering and cement. (you can find one by asking your local optometrist)
-- Pat Raymore (email@example.com), March 01, 2002.