Back in November I picked up the vintage Canon FD 35 f/2 Concave - Chrome Nose lens. On a trial outing I took along the FD 35 f/3.5 S.C.for some comparison shots ...
The
thorium element(s) of the 35mm f/2 lens had yellowed due to radioactive decay and the warm character shows in it's colour
rendition. The second image was shot with the 35mm f/3.5, no colour correction has been applied to either image but obviously, I could cool or warm the resulting images in post processing if desired. But these two images were made with direct comparison in mind.
I have since set up a rudimentary treatment process to expose the lens elements to UV-C light which can remove some of the yellowing of the thoriated lens element. The results are temporary as continued radioactive decay will yellow the lens on an ongoing basis. Wait ! Radioactive ... yes I said radioactive, but not to the degree where it is dangerous or even a health concern and I don't sleep with the lens under my pillow. FYI - a few decades ago thorium was added to some optical glass formulas to improve optical performance and the Canon 35mm Concave and other lenses are revered for their sharpness. As for clearing some of the yellowing, it's an experiment in process with some improvement shown.
note:
I lost track of what aperture I was using and was shooting handheld which required light cropping adjustment afterwards to align the. I really want to repeat the exercise with the camera tripod mounted shooting a range of apertures for comparing sharpness of each lens across settings ... and now I have a FD 35 f/2 S.S.C. Concave and FDn 35mm f/2.8 that could be added to the mix ;-)
DJE
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