Blacking lens edges

darinwc · Nov 26, 2017

I have a nice Canon lens where the black paint around one of the elements had completely separated. I tried using some black paint. However it did not seem to "seal" well against the frosted edges of the lens. So there is still quite a bit of light bouncing around.
I would appreciate some advice on how to properly black the edges. Thanks!

Europan · Nov 26, 2017

I use a felt marker.

AgX · Nov 26, 2017

I got several lenses with a "sparkling" glow at the ground edges. At some it is really strong. Without disassambling so far I assume it is delamination of the black varnish at the pits of the ground surface.
Witch means the varnish layer is at its outside visually intact, but air entered into the pits.

Experiments with fresh varnish on vrigin ground surfaces were satisfactory.
Did you not take off the old varnish completely before applying the fresh layer?

Patrick Robert James · Nov 26, 2017

There is a special paint for it IIRC.

I've used Speedball Super Black Ink in the past which is basically india ink in shellac. It works fine for that purpose. I've also used a Sakura pigment brush pen. The pigment makes it opaque. The Sakura is easier to use and they don't cost much. Both require a couple coats at least. Sharpies work sort of, but they are not opaque. You really need something opaque.

Hope that helps.

Poisson Du Jour · Nov 26, 2017

Pot belly black or flat black paint applied with a fine point sable brush. Two pass coating does the job.

shutterfinger · Nov 26, 2017

Golden Heavy Body Artist paint #1040 Carbon Black http://www.goldenpaints.com/products/colors/heavy-body
Dilute 1:1 with water, paint with a fine bristle artist brush, use 2 thin coats.
Clean the glass with acetone prior to application.
http://www.michaels.com/ caries Golden artist paints.

paul ron · Nov 27, 2017

Poisson Du Jour said:
Pot belly black or flat black paint applied with a fine point sable brush. Two pass coating does the job.

+1.

you have to be sure to get right to the very edge of the clear part of the glass or you will see a glow from the spots you missed.

multi coats are the way to go.

BrianVS · Nov 27, 2017

Europan said:
I use a felt marker.

That's what I use- a Black Sharpie. It works well, the last I used it on was a 1937 CZJ 8.5cm F2 Sonnar. "Like night and day".

AgX · Nov 28, 2017

You all are missing my point.
If the sparkling is due to delamination (my thinking) then just painting over woud not do the job.

jim10219 · Nov 28, 2017

I haven't had any problems with paint sticking to glass. And I've used several different types of paint over the years (acrylic, oil, enamel, permanent marker, spray paint, India ink, etc.). The trick is preparation of the surface and allowing the paint to fully cure. If you're paint isn't sticking, then you probably need to do a better job of preparing the surface and make sure to allow plenty of time for the paint to cure.

Nothing is permanent on glass, however. It can always be scraped off or dissolved with chemicals. Keep that in mind. That's why I use plate glass for my pallet when I paint. When I'm done with a painting, I just let it dry, then scrape it off with a razor blade. But, pretty much all of the paints stick well enough when it is properly prepared and cured for what you're trying to do.

paul ron · Nov 28, 2017

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AgX said:
You all are missing my point.
If the sparkling is due to delamination (my thinking) then just painting over woud not do the job.

you are absolutely correct! if the paint was delaminating, just painting over is a band aid on an infection. the old stuff has to be removed first and cleaned very well before repainting.

darinwc · Nov 29, 2017

The old paint was completely removed.
The edge was just the white frosted glass left.

The problem was that the paint did not do a good job of getting into the texture of the frosting. So looking from the other side, it was still white.

I will retry with a thinner paint mixture.

AgX · Nov 29, 2017

Thus, seen your experience, could it be that such sparkling surface was there from the start and not from partially delaminating??

BrianVS · Nov 29, 2017

Posting some close-ups of the affected area would help. My Canon 50/1.9 had the paint come off in such big flakes that it looked like the aperture blades were floating around loose. It was quite easy to separate the remaining paint from the glass, and use the Black sharpie to get rid of reflections. This worked well, the lens was $50. As was the Canon 5cm F2 that I got along with it. The paint was intact on the Canon 5cm F2.

shutterfinger · Nov 29, 2017

Sounds like the paint you used was too thick to settle into the gaps between the frosted edges. Thinned paint in 2 or more coats should work.
I use one of these for small areas https://www.amazon.com/Birchwood-Casey-Super-Black-Touch/dp/B00BGH0Y0W
better than a felt pen.

Nodda Duma · Nov 29, 2017

AgX said:
You all are missing my point.
If the sparkling is due to delamination (my thinking) then just painting over woud not do the job.

You have to remove the old paint with solvent.

Professionally, for edge-blacking my optics, depending on the specific application I've used:

- Sharpie (for space optics, quick and dirty check of stray light, or minor touch-up)
- Speedball India Ink (pretty much every other application)
- Specialized, really expensive black epoxy paint formulated to meet a mil std that I can't remember at the moment (for those times when the lenses have to be edge-bonded with adhesive incompatible with the other two options, or when a customer thinks he's special).

I don't really use anything else, and my choices are typical for the optics industry.

But, whatever blackens the edges without interfering with the mounting of the lens in the barrel will probably be just fine.

paul ron · Dec 2, 2017

btw one more point... the edges have to be completely blackened right up to the clear glass line. if you wavered ever so slightly at the line near those edges, you will still see the white line where you missed.

i tend to go over the edge right on the clear and clean it later with a razor. if you use a brittle paint, you will never get it right. time to razor is right at the time the paint is almost cured, still slightly tacky but doesnt pull as you razor.

Blacking lens edges

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