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EL-Nikkor 50mm f/4 balsam cementation repair

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#1 Steven B.

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Posted 20 April 2017 - 21:45

I bought for a very good price an EL-Nikkor 50mm f/4 few weeks ago. I was very disappointed by the quality of the pictures, especially in UV.

I closely inspected the lens: the front group was perfect, but the rear group seemed very "cloudy". Illumination with a 365nm torch clearly showed a defect in the rear lens group (fungus, balsam separation ? I still don’t know...).

Looking at the price of this lens, I had nothing to lose trying to repair it.

Here is the way I proceeded - with detailled instructions if you want to try by yourself.

1/
Unscrew the front part by pressing down and turning the lens against a piece of rubber. Hold the body firmly, not the aperture setting ring.

Attached Image: 1800IMG_1164.jpg


2/
Lens is now open.

Attached Image: 2800IMG_1166.jpg


3/
To open the back part use a piece of rubber which needs to be cut at to size. Add a piece of paper towel to avoid friction of the lens against rubber.

Attached Image: 3800IMG_1167.jpg


4/
Unscrew the back part by pressing down and turning the lens against this piece of rubber.

Attached Image: 4800IMG_1168.jpg


5/
One could think there is a retaining ring holding the rear lenses group, but it is only the shape of the body. So here there is nothing more to unscrew.

Attached Image: 5800IMG_1169.jpg


6/
The only way to extract the rear group is to push it away from inside of the lens.
If you still have the lens case it will provide a good holder. Put a piece of paper towel in the bottom to avoid lens damage during extraction.
Fit the lens body into the bottom of the box and press down on the rear lens group with something like a pen body protected with electrical tape at its end. Take care to not touch the diaphragm blades.

Attached Image: 6800IMG_1171.jpg


7/
After collecting the rear lens part I realized that a simple cleaning won’t be enough as the problem was located in-between the 2 lenses of this group: colored/cloudy balsam cementation.

Attached Image: 7800IMG_1172.jpg


8/
I first tried to re-melt the balsam using a hot air gun. (A specific heat protection blanket was placed under lenses).
It worked ! But the problem was still there: an inspection with a 365nm torch still showed a foggy cementation.

Attached Image: 8800IMG_1155.jpg


9/
I heated the lenses again at 250°C (with a LCD temperature control hot air gun) but that time without allowing cooling in order to separate the lenses.

I cleaned them using acetone to remove the old balsam. No scratchs, lenses were clear and clean !

Attached Image: 9800IMG_1173.jpg


10/
Now I had to glue them again. This has been done using UHU glass glue.
This kind of glue is a UV curing type, so work in an UV free environment.

Put a (very) small drop of glue in-between the 2 lenses and rub them together to avoid any air trap. Carefully remove excess glue and place the group back into the lens body. You can then screw the back part that holds the group in place.
When everything is OK (check there is no glue on lens surface) let the glue cure by placing the lens in the sunlight or by using a UV torch.

Note:
Proper personal protective equipment must be worn for your safety. All of the 365nm torch, heat air gun, UV glue, and acetone can be harmful to your health.

Here is a test picture of the repaired lens with a Ulex europaeus found in the port of Cork (Ireland).
Equipment [Nikon D3200-broadband + EL Nikkor 50mm f/4]
Ultraviolet Light [f/11 for 4" @ ISO-400 with Canon 199a modified Flash and Baader UV-Pass Filter]

Attached Image: DSC_7905 copie.jpg
Steven B.

#2 nfoto

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Posted 21 April 2017 - 05:57

Apparently your efforts paid off nicely. The UV rendition of the Gorse is as expected :D

Thanks for the detailed instructions.
Bjørn Birna Rørslett

#3 enricosavazzi

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Posted 21 April 2017 - 20:23

I did a similar repair on a Macro-Nikkor 12 cm f/6.3. I left the front doublet (which was the problem in this case) for a couple of weeks in a sealed vial with a mixture of methyl and ethyl alcohol, and the elements came out clean. I reassembled the lens without cementing the doublet, and have not noticed any problems with low contrast or flare.
-- Enrico Savazzi

#4 Steven B.

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Posted 21 April 2017 - 22:46

Good to know there is an other solution to separate lenses from a group cemented with this organic resin.

I first thought about reassembling the lenses group without any glue. But, placing the lenses one against the other made appear Newton rings.
That said I did not try to shoot with that lens in this condition and so can't tell if it brings problems or not.

Solution of using UV-cured glue comes from my research on various other forums where this way to proceed has given several times satisfaction. It also seems that UV-cured glues are now commonly used by optical manufacturers.
UHU glas glue or Loctite AA 350 as an other example are maybe not from the best quality for this kind of job but the remaining glue thickness is so thin that it does not seem to change significantly light transmission.

Edited by Steven B., 22 April 2017 - 15:42.

Steven B.

#5 Andrea B.

    Desert Dancer

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Posted 22 April 2017 - 13:29

Thank you for this useful post. Another member discovered some haze in his EL-80, so perhaps he can repair it using these guidlines.

When you find the time, please post your Ulex to the botanical UV-signature board. It is a nice shot. "-)
Andrea G. Blum
Often found hanging out with flowers & bees.