Schneider-itis: The Perennial Problem

[Michael R]

Without having made the identical photograph under identical lighting conditions with the identical camera, identical film/exposure/contrast index, pre and post schneideritis I’m not sure anything can be concluded here. As for sending it to Schneider for repair, be prepared for a huge price tag on that, if they will even do it.

One of my last, great 8x10 lenses, a 210XL, is still working very well, but I recently noticed last time I used it that contrast could have been better.
Sure enough, it's got the Schneider-itis.
I wasn't using it much last year, so the infection got ahead of me. Here it is:

IMG_6770 by Ari4000, on Flickr

Given it's a very valuable and expensive lens, I would like to solicit some opinions about what I can do next.
I ordered some Black 3.0 paint for another lens with inner reflection issues, and I'm wondering if I can use that paint on the inside of the 210.
I feel pretty good taking the lens apart. And I don't plan on ever selling it (never say never), so if the repair is ugly, but it works, I'm a happy guy.

Other suggestions? Repair costs? Is there a pro out there who would tackle this and do a good job?
Thanks

[Ari]

Definitely impacts contrast, yep.

You would have to take the old stuff off with a soak in solvent (denatured alcohol or acetone), clean off the rest, then reapply. It is not easy to get it right, but practice makes perfect.

One note: gloss black works better than flat black.

Thanks, Jason.
Do you have a recommendation for a specific paint?

[tomwilliams]

One note: gloss black works better than flat black.

This seems counterintuitive to me. I would expect a flat black to dampen reflections better than a glossy finish. In the astronomical optical assemblies I'm familiar with, a flat black is preferred. Is the gloss finish better for some other reason?

[Ari]

What I've read so far is that glossy will adhere to the glass surfaces better, but maybe Jason can confirm that it's what he meant as well.

[John Layton]

I'm wondering if the micro profile of the elements edges would make the issue of mat vs gloss paint moot. In other words, the lightly ground texture of the elements edges would effectively create a mat surface to otherwise glossy paint. Jason does this make sense?

[Nodda Duma]

This seems counterintuitive to me. I would expect a flat black to dampen reflections better than a glossy finish. In the astronomical optical assemblies I'm familiar with, a flat black is preferred. Is the gloss finish better for some other reason?

Those are two different applications for mitigating stray light.

Here we are talking about edge blackening of a lens, where the edge is ground and you want the pigment to flow into the micro-cracks of the ground surface to scatter stray light paths intrrnal to the lens. Gloss paint typically has smaller molecules than flat paint.

In air spaces such as your telescope reference, a flat black is desired to perform the scattering, as there is not inherent structure equivalent to ground glass…it’s just air (or vacuum).

That said, a solvent based ink (India ink) with very little binder and very fine carbon pigment works almost as well as gloss black.

[ridax]

(1) I usually check the direction of any possible reflections from the surfaces I am going to paint black. If any of the reflections can go directly to the image plane, I use mat black. If not, I prefer glossy black; thus the direct reflecting light rays get onto another black surface which reduce their intensity more - while a mat surface would send a part of the stray light directly onto the film plane.

(2) I'd think twice before disassembling an aspherical lens. Those are usually made up to very strict tolerances - much more strict than the ordinary spherical lenses are. And if I decide to disassemble an ASPH, I'd take care not to turn the elements around the axis either (to say nothing about the distances between them). That probably means the new black paint layer should be exactly the same in thickness as the old one was. And if the old paint layer was not even, then the new one has to retain exactly the same thickness differences on the element sides....

(3) To remedy the contrast loss, I'd probably just pay more attention to my lens hoods than go into the trouble of re-blackening the shneideritties.

[ic-racer]

It is nice to have good-looking equipment, but I usually don't bother to restore the cosmetics on these as it not being worthwhile. I just live with it.
Of course I'll let the lens designers chime in as to any optical benefit of edge painting, when only the edges visible to the consumer are painted and the rest of them are unpainted.

[Nodda Duma]

It is nice to have good-looking equipment, but I usually don't bother to restore the cosmetics on these as it not being worthwhile. I just live with it.
Of course I'll let the lens designers chime in as to any optical benefit of edge painting, when only the edges visible to the consumer are painted and the rest of them are unpainted.

The lens designer chimed in above

[xkaes]

I think it would be pretty easy to estimate the amount of contrast loss in the lens -- if any -- with a simple comparative "step" test.

Then if there is any worth dealing with, test to see if changes in development, using a lens shade, etc. could remedy the problem.