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specific term for issue
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PostPosted: Wed Nov 20, 2019 6:32 pm    Post subject: specific term for issue Reply with quote

Hi guys. I have a Canon FD 50mm 1.4 SSC with an issue I have seen in various lenses from time to time. The darkened edges (ie non optical side parts of lens) are whitened by flaking paint or fungus or something. Does this have a specific term? I imagine it would reduce contrast somewhat as it would increase the amount of light bouncing around in the lens. Thoughts?


PostPosted: Wed Nov 20, 2019 7:07 pm    Post subject: Re: specific term for issue Reply with quote

jamaeolus wrote:
Hi guys. I have a Canon FD 50mm 1.4 SSC with an issue I have seen in various lenses from time to time. The darkened edges (ie non optical side parts of lens) are whitened by flaking paint or fungus or something. Does this have a specific term? I imagine it would reduce contrast somewhat as it would increase the amount of light bouncing around in the lens. Thoughts?

There are several causes each of which will have a different term/phrase to describe it.
One other possible cause you didn't mention is corrosion, aluminium compounds are typically white.

You are right about it's likely effects, more reflections of stray light hitting the lens body will reduce contrast. I don't think there'll be any other optical effects, but if particles from it could get into other regions it might have further issues later...

A few photos of the affected areas might enable us to have a better guess as to the cause.


PostPosted: Wed Nov 20, 2019 7:30 pm    Post subject: Reply with quote

I have seen similar things in folder lenses caused by paint peel. This, I think, is something different. Doesn't look like fungus to me. It looks like maybe the agent used to bond the lens element to the bezel is peeling away. Anyway, I am planning to sell the lens and wanted to describe it without completely scaring off buyers.




PostPosted: Wed Nov 20, 2019 7:38 pm    Post subject: Reply with quote

Looks like the paint is separating from the elements, about the only thing you'll notice is a loss of contrast.
This is an easy fix for a repair tech.


PostPosted: Wed Nov 20, 2019 8:42 pm    Post subject: Reply with quote

Aluminum oxide from the body was my first thought too. Others make me think yes paint peeling off body inside lens mounts. Oxidation building lifted paint. Looks really cool! lol Oofs wide open might look interesting...


PostPosted: Wed Nov 20, 2019 9:23 pm    Post subject: Reply with quote

There's 'Schneideritus' as it's popularly called. As per my Componon here -



I used to ink in the edges of Schneider elements suffering from it until I read often, and realised myself, that it seems to have no impact on performance. I've never looked into what is going on, but looking into 'Schneideritus' might give you a start on tracking down the answer for yours Jameaolus. Just an idea.


PostPosted: Wed Nov 20, 2019 9:43 pm    Post subject: Reply with quote

That looks cool too! lol. Can be seen in oof highlights?

Another thought about the first lens. Suspect since we can see through lens paint peeling from lens body, element edges are unpainted, designers counting on dark paint inside mount instead. Somebody who works on these can tell us are the elements edges painted?

Not sure about these, most 50s are easy to open & clean.


PostPosted: Wed Nov 20, 2019 10:45 pm    Post subject: Reply with quote

visualopsins wrote:
That looks cool too! lol. Can be seen in oof highlights?



You know, that's food for thought. I can't remember looking there. Now I will. Thanks visualopsins.


PostPosted: Thu Nov 21, 2019 2:38 am    Post subject: Reply with quote

It's outside the optical path, but it will decrease contrast due to the increased reflectivity.


PostPosted: Thu Nov 21, 2019 9:52 am    Post subject: Reply with quote

Schneideritis, seen from in and outside:
http://www.4photos.de/camera-diy/Schneideritis.html


PostPosted: Thu Nov 21, 2019 4:40 pm    Post subject: Reply with quote

Lightshow wrote:
It's outside the optical path, but it will decrease contrast due to the increased reflectivity.


Part of optical path when light reflecting from whateveritis off the inner surface of the front element, back into the lens optical path decreases overall contrast. I.e., there's no way it causes effect unless it's part of optical path...


PostPosted: Thu Nov 21, 2019 5:21 pm    Post subject: Reply with quote

I have some lenses with schneideritis (though I didn't know it was called that). Also some older folder lenses where it is obvious the paint has disconnected from the edge of the lens and flaked off. This kind of reminded me of delamination though, just the way the weird patterns formed on the side of the elements.


PostPosted: Fri Nov 22, 2019 6:09 pm    Post subject: Reply with quote

When I was looking for a Vivitar 35mm f2.8 T4 lens, I saw quite a number of them having this "issue".


PostPosted: Fri Nov 22, 2019 9:45 pm    Post subject: Reply with quote

From the image provided, I would also suggest paint or a blackener applied to a lens element edge
is separating from the glass.

Also from the provided image, I am guessing that the glass edge is a rough finish,
such as a sandblasted surface or from a rougher machining process.
Obviously, it is not a polished surface.

Now, my gut reaction is that I'm looking at a bonded/cemented pair of glass elements,
with the element behind providing a reflection. If not that, then a single element
which was bonded to an outer ring or assembly.
Furthering my gut reaction, and this is because I've seen very similar before
in microscope or telescope or sextant or some other opticals I dismantled
decades ago as a child, is that the blackening has remained firmly affixed to
whatever cement has been used, while coming loose from the rough glass edge.

I saw this same condition when dismantling something optical.
I was a child of about 12 years old, and the item was deemed by adults as worthless.
It was an old item, decades old at the time. I'm fairly sure it was a sextant.
I had free reign to do with it what I pleased, so I dismantled it in my curiousity.
I specifically remember seeing this same condition before dismantling, and found
exactly what the condition was, as I described above.

I may or may not be correct about the issue, but I have experienced almost
exactly the same in first-hand experience.