petzval crown glass "repair"

[eddie]

hello all,

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 (http://photo.net/photodb/folder?folder_id=954057). many to check out. start at the bottom and work up.

the 1st photo below is the original sellers photo of the missing piece.

cheers

eddie

[eddie]

i will probably have to fill in the scallops.

be sure to see all the photos in the above link.

[Glenn Thoreson]

I would think if you blacked out all around the thing, enough to cover any flaws, it would just act as a diaphragm. Smaller f/stop. It probably wouldn't have much effect on the swirlies and bamooka (or whatever you want to call it). :D

[BarryS]

Thanks for posting; I'll have to remember your trick next time I find some bad glass. I'd bet the lens performs almost identically to one with perfect glass. I remember reading about how Sally Mann would go lens hunting and she had a hard time finding lenses that would be damaged enough to significantly affect the image. In my SLR/Zeiss days, i used to think glass had to be microscopically pristine. Now with old lenses, I know better.

[eddie]

thanks guys.

glenn, i think you are right. i may fill the scallops in with some magic glue or maybe just some black ink. stay tuned for photos.

eddie

[77seriesiii]

Another option is Canadian balsam, but it probably doesnt dry as fast as the 'magic' glue.

No matter how you slice it, you brought back a great old lens, awesome job Eddie.

./e

[Steven Tribe]

Looks like a very good solution to serious edge damage. I have seen (but never owned)a lot petzvals with this rear damage. I have always assumed it was on projection lenses with the extreme heat generation in the tin box that was the cause. My projection petzvals are very well put together at the rear with fiber gaskets which seem like a expansion precaution.

[eddie]

another thing i just noticed. this lens has no focus knob. it has been removed. as a result the gasket material between the barrel and the outer barrel is gone. this is usually always the case when the focus knob is gone....so is the gasket material. this is because the gaskets fall out when the two barrel are separated.....or probably more to the story they do not go back together easily so people take them out. anyway i just happened to notice i have light leaking through the gap. i know that should be obvious if i had thought about it.......

anyway, NOTE to self. anytime the focus wheel is missing on lenses be sure to seal any light leak between the barrels.

eddie

[cdholden]

India ink works well for scratches.
If you're coloring on the side, wouldn't you want to do it all the way around, like an iris aperture, so light entering the element will pass through evenly? I would think only coloring the scallop damage might cause uneven exposure of the film/plate.
Chris