Author Topic: Nikkor AFD 20mm - glue separation suspected  (Read 793 times)

Zang

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Nikkor AFD 20mm - glue separation suspected
« on: January 17, 2021, 08:38:27 »
Hi all,

I posted a question regarding glowing issue with AFD 20mm a few days ago. Upon closer investigation, I found one of the inner, rear element shows full of tiny white dots. The dots look pretty regular, dense and they are all over the lens surface. They are not likely dust. My immediate suspicion is, the glue of the duplet deteriorated (glue separating issue).  I'll probably take the lens apart but does anyone know if glue separation is possible to fix?

Cheers,
Zang

MEPER

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Re: Nikkor AFD 20mm - glue separation suspected
« Reply #1 on: January 17, 2021, 09:03:32 »
In the old days where Canada Balsam was used it seems to be a "DIY-job" but probably hard to align the two lenses 100%.

http://forum.mflenses.com/re-cementing-doublet-elements-with-canadian-balsam-t34467.html

Acetone or similar was used to get the two cemented lenses apart.
 

Birna Rørslett

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Re: Nikkor AFD 20mm - glue separation suspected
« Reply #2 on: January 17, 2021, 10:34:06 »
Element separation typically is seen towards the edges as a discolouration or darker zone. Tiny white specks in a lens smacks of fungus, sorry to say.

Zang

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Re: Nikkor AFD 20mm - glue separation suspected
« Reply #3 on: January 17, 2021, 15:21:28 »
No, you gave me hope. Fungus is easier to deal with than glue issue. One of the challenge with glue is how to separate the elements...

Matthew Currie

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Re: Nikkor AFD 20mm - glue separation suspected
« Reply #4 on: January 17, 2021, 16:10:56 »
This has come up before here, but I'll mention it again.  I have a 20 mm AFD lens which had a fogging problem in the glued element.  Apparently for at least a short run Nikon used some unusual cement here, and it's not easy to fix.  My local repairman did some research and determined that regular balsam was a not used.  I tried getting a new element from China using the Nikon part number, but the wrong part came, and I despaired of being able to get the right one from their nearly indecipherable site, if it even existed.

The repairman has done this job before, and prefers not to, owing to the difficulty of alignment, but he tried it this time, with a more modern synthetic cement that was said to be like that used by Nikon.  Unfortunately, the lens came out unacceptably soft. He suggested that the cement they used probably has a unique refractive index. He was up front about the possibility of getting the alignment bad, and the resulting lens's softness was very even, so I don't think the problem was that.   The attempt ended there, as he was unwilling to charge for the failure, but understandably reluctant to keep trying.

Another poster here later noted that this lens, along with another (the 180 D I think) were known to have this problem, and he had had one repaired by Nikon, but my recollection here is that it was pretty expensive, and not in the US (South Africa, maybe).

So let's hope that the problem is fungus or something else not inside a glued element, of which I believe that lens has more than one.

Zang

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Re: Nikkor AFD 20mm - glue separation suspected
« Reply #5 on: January 17, 2021, 17:36:51 »
Hey Matt,

Now as you mentioned, I recall you were telling this before on one of my threads.

I may be wrongly telling about dots, but they are that tiny and many so maybe Matt's fogging term may describe it better. I check it by using a reversed wide angle lens as a magnifier.

BTW, I torn down the lens, probably more than I need to get to the rear block, but more update to come soon...

Matthew Currie

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Re: Nikkor AFD 20mm - glue separation suspected
« Reply #6 on: January 17, 2021, 18:29:57 »
The wrong part that I got is an element of approximately 21 mm diameter, set into a metal frame.  On one side, the lens is slightly convex and protrudes from the frame, and the other side is set deeper into the frame.  If, by some chance, that's the part that is bad on yours, it might be possible to send you mine.  I believe it's the glued element fairly near the rear, as the one needed on mine was apparently quite deep in.

Since I have since gotten the AFP 10-20, and also routinely use the 16-80 DX, I don't really need another 20, so have no expectation of bothering to fix the one I have unless the parts fall into my lap.

Zang

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Re: Nikkor AFD 20mm - glue separation suspected
« Reply #7 on: January 17, 2021, 18:37:50 »
Hey Matt,

Thanks Matt for your offer! The tricky part is, the foggy element is within the rear block which is sealed. I do not think I can disassemble it. I cleaned the surfaces and put everything back. When I said foggy, I meant I did not see it foggy by naked eyes. I can only notice kind of universe of tiny dots when I used the magnifier to look through the glass.

I am doing some testing and will update with the result soon. No magic is expected, though, as I did not fix anything.

Zang

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Re: Nikkor AFD 20mm - glue separation suspected
« Reply #8 on: January 17, 2021, 19:29:50 »
When I cannot find the bad test pictures (I probably deleted them), the tests from today do not look very bad at all. Could be because it is a bit cloudy here today and the light is not very hash. The two picture below were taken with f2.8 and f8. I was lazy so I took them on my cropped D300 as I had it on my desk. You can still see some glowing, but the contrast of the subjects around the white bucket is still decent. Before, the surrounding subjects looked blurry.

Zang

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Re: Nikkor AFD 20mm - glue separation suspected
« Reply #9 on: January 17, 2021, 19:33:22 »
More samples...

Zang

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Re: Nikkor AFD 20mm - glue separation suspected
« Reply #10 on: January 17, 2021, 19:35:49 »
A picture with strong light refection on it...

Matthew Currie

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Re: Nikkor AFD 20mm - glue separation suspected
« Reply #11 on: January 17, 2021, 20:28:51 »
Those pictures look not bad.  Way way better than mine was.  Mine were foggy and nearly devoid of contrast before the attempted repair, and soft after.  I looked at the wrong part I got and it appears to be actually the rearmost element which screws in, and probably is not a glued up one at all.  There's another small lens loose underneath that one.  The problem element in mine was much deeper than that, requiring considerable disassembly.

Zang

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Re: Nikkor AFD 20mm - glue separation suspected
« Reply #12 on: January 17, 2021, 20:51:06 »
Thanks Matt. I'll give the lens another test ride on my FF D800 outside today to have more checking.

Zang

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Re: Nikkor AFD 20mm - glue separation suspected
« Reply #13 on: January 17, 2021, 23:17:09 »
Ok, so the lens is pretty low contrast. I boosted the contrast a bit in all the pictures below. The first one was when I was able to reproduce the glowing issue. I lower the view point a bit in the second one and the issue was gone.

Zang

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Re: Nikkor AFD 20mm - glue separation suspected
« Reply #14 on: January 17, 2021, 23:18:23 »
This one was very low contrast and below is result of quite a bit contrast boost.