Introduction: Fixing the Dreaded Scratch on Rear Element of a Lens
I acquired this lens on an "as-is, no returns, are you that !&##*% stupid to be buying this" auction deal. This is a Rodenstock 300mm f9 to f64 APO- Gerogon lens made for an enlarger but easily adaptable to a large format soviet FKD 18x24cm view camera. The lens was only a few dollars for good reason--on the rear element there was a cluster of nasty deep gouges well past the coating into the glass. Rear element scratches are considered lens fatal with no redemption. Lets see what I can do with this
Step 1: Another Look at the Damage at Hand
Yessir, that is a nassssty cluster of scratches--I always wonder how these sorts of things occur..? Juggling accident? Minor shotgun blast? good lord. I wonder what photographic effect they have? On to the 1st test shot
Step 2: Boring Backyard Shot Showing the Effect of the Rear Element Scratch
Xray film 2 seconds at f64. Developed in xray developer diluted 1:40 for about 5 minutes. The scratches manifest themselves as a soft area of a lighter density right smack in the middle. This is why lenses that suffer this sort of damage generally get tossed or are used as paperweights
Step 3: Yep---I'm Going to Use an Automotive Windshield Chip Repair Kit on That Bad Boy
They sell this one-shot kit at most automotive parts stores for about $10. You get a tube of epoxy and a injection pedestal and syringe. This is intended to repair a stone chip without taking it to a glass shop or replacing the entire windshield. We are going to fix a lens with it
Step 4: Using the Repair Kit on the Lens
Follow the directions in the kit--you peel off one side of the adhesive gasket that holds the injection pedestal and place it on the glass, Peel off the other side and stick the pedestal in place. Squeeze 3/4's of the small epoxy tube into the hole and insert the syringe. Shoot the goop in there and hold it for 15 minutes or so.
Remove it all carefully peeling off the double sided sticky base--there is one more step with a slight modification--
The kit comes with a small square of tranparent plastic. For a car windshield you'd smear some of the remaining epoxy you held back onto the small plasic square and place it over the repair and cure it in the sun for 15 minutes.
The plastic square does not fit the contour of the lens so I used a small bit of cellophane in it's place that forms to fit the glass. Let it set for 15 mins and remove it and clean the lens with a soft cloth with some alcohol on it
Step 5: The Lens Post-repair
Looks are a little deceiving here. While the scratch is *visible* I can no longer detect it or just barely a whisp of it with my fingernail dragging across. It was very deep and was more of a chunk missing truth be told
Step 6: Post Repair Test Shot
Again, Xray film f64 2 seconds in Xray dev diluted 1:40 for about 5 minutes. While it's not 100% gone one has to argue it's a helluva lot better and $10 for the kit was money well spent I think. Of course your results will vary depending on severity of the scratch and this one was really bad. If you are singing the blues after a lens mishap and you have a pricey piece of glass thats looking at the junk heap--what do you have to lose vs what might be gained?
Step 7: Some Editing on the Raw "after" or Post-repair Image
Tiny bit of embellishment/editing done with the dodge/burn tool in GIMP--all of about 40 seconds to smooth out the last bit of defect remnant visible on the 2nd test after the chip repair. Can you see any real quality issues all said & done? $10 fix looks good to me--not perfect but MUCH easier on the leftover editing
1 year ago
I wonder whether you considered using a black filler/paint of some kind for the scratches. The windshield epoxy will almost certainly not have the refractive index of the glass it replaces, but it does transmit light. The blackened scratches might cause a bit of diffraction, but I suspect that would be less detrimental than epoxy messing with the refraction.
How did you get the epoxy to go/stay only in the scratches? On windshields they seem to rely on capillary action drawing it into the cracks, but your lens scratches are more like 'open trenches'. I admire your courage! :-)
4 years ago
I've got some eyeglasses that have this problem. I went to the local auto parts store and saw they had those kits but decided to see if anyone else had any luck. And there you are.
Reply 4 years ago
That's great gralan! I get 2 pairs a year on my employer supplied insurance and without it, it would be big bucks to replace a pair. Did it work out for you with negligible loss of quality?
6 years ago
you have to make a test shot when you got flare in the lens, or a direct sun ray in the picture to see the damage, or the effect of fixing, adjusted to infinite, so you can explore also the ugly dust inside of the glass
Reply 6 years ago
Its a barrel lens with no focus of it's own on a 18x24cm (roughly 5x7) view camera. I am focusing on a scene about 70ft away. I suppose I could torture test it some more but realistically here we have 2 shots--1 pre repair showing the fault and 1 post repair with the fault dramatically reduced taken of the same scene (apples to apples). Of course the fault will still be there if I was trying to get lens flare--it is in the 2nd shot but with minimized effect.
Reply 6 years ago
Oops 18x24cm is 8x10 in. ....13x18 is 5x7 my bad
6 years ago
You are innovative. Saved this lens from the junk drawer or trash bin. Congrats!
6 years ago
Will try this - scratched an OK pocket camera when the lens shut & a grain of sand ground into it. Wondered about whether I could fill it & this never crossed my mind...