Dan and Brian, I've taken a bit of time to look more closely at the one lens I have that shows the schneideritis effect. That is an older 135 all chrome componon enlarging lens. Yes removed the front element per above questions. The body of this lens appears to be all brass but shows extensive schneideritis when viewed thru the front element. Highly visible thru the front element when viewed at 25 and 50X with a binocular microscope (Wild M3). I think I convinced myself that the effect is confined to the beveled edge of the front element possibly where the black edge coating has worn thin to reveal a ground edge glass in spots that are about 2 to 100µm in diameter, (used a calibrated eyepiece reticle to measure). So Dan is on the right track here. Since the edge is captive one could assume there would be no contamination to the optic surface. But close examination reveals tiny bits (specks) emanating out from the lens edge, well into the optical path. These look like grit from the ground edge; higher in concentration nearer the edge then dwindling to few about 1/4 way to the lens center. Probably little to no effect on the lens performance.
Next I looked at a 110 SSXL (not disassembled) which at first (with the unaided eye) showed no schneideritis; but thru the front element showed many spots of whitish pinprick blooms on the blackened aluminum housing under the from element. I think this had to be on the aluminum since the machining showed the stepped contour for internal scattering reduction. The size of these white spots were small from 5 to maybe 25 µm; probably creeping schneideritis. But I've seen worse cases of this in the blackened aluminum housing on a few other lenses I've used.
I think there are at least these two causes of schneideritis, unrelated to each other in origin but may appear similar to the unaided eye. Certainly a cause for confusion by me and others.
Nate Potter, Austin TX.
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