just thought i would pass on a "repair" i did on a new-to-me petzval lens.
i got it as i have a parts lens of almost the exact one....well, it turned out to be 500-700 serial numbers off and a bit different.......
anyway, i did not take a photo of the broken part before i began as i forgot my digital camera so i will use the original sellers photograph of the busted part. because the crown glass is so thin on the edges having impact damage caused everything to be a bit out of whack. so the missing piece caused the surrounding glass to receive extra force on removal and install of the glass in the barrel. it was sitting lop sided. so much of the outside edge was broken. scalloped chips also happened on the flat surface. as a result the glass was no longer round and did not want to sit into the barrel correctly. the spacer ring also did not sit correctly on the crown glass causing more damage to it and a scallop mark on the flint glass as well.
i use this two part urethane epoxy/glue at work. we call it "magic glue" as it is magical. it come in 30 sec, 1min, 5min, 15 min, 30 min for different applications. i used the 1 min. i used a piece of clear packing tape on the lens with a couple of mm sticking past the edge. this way i could replicate the curve of one side of the glass. i then added the magic glue. i filled in the broken area and around to the opposite edge. after the "exact" amount of time i peeled the tape from the back side of the glass and used a razor blade to get the magic glue into the exact shape i needed. i used lacquer thinner to take off the bit of excess MG from the lens. it was not perfect but close enough. i figured if i tried it again i may F it up. i then sanded the edge to get it round. (the taped side worked perfectly. it fit the curve with no need for sanding or anything.
after all this it fit into the barrel correctly. the spacer ring sat correctly again. and the flint glass was now back into its correct placement as well.
i figured that it probably would have worked even with the piece missing. but when i saw how bad the rest of the crown glass was i thought i would try some "Fix". the black magic glue will keep the chip from shooting stray light around. i bet it does not affect anything. the scalloped breaks have me a bit worried. i will test it to see what happens. i plan to use a permanent marker or india ink to blacken the scallop marks if i need...should work fine. i did not do it yet as i did not want the repair to look that much worse.
please see more photos here. many to check out. start at the bottom and work up.
the 1st photo below is the original sellers photo of the missing piece.