Nikkor AF 20/2.8 D: Stuck aperture blades, lens clouding

I could purchase this lens cheaply.

The aperture blades are likely oily and there is some clouding around the rear lenses.

I looked at what I can do for the nice 20



Externally in mint condition.




The clouding in the rear optical component under focused LED light.




... and under diffuse LED workplace lighting.

The clouding is not visible here.




The rear optics can be easily unscrewed.




I can only loosen the screw connection …




… with plenty of acetone, which I apply through the opening and directly onto the thread.

This leaves marks and removes some of the black surface coating.

But it's just a cosmetic problem.




All three lenses are removed.




The clouding is located in the rearmost lens, which consists of two cemented parts.

Unfortunately I can't do anything about that because I cannot separate the lenses.

A case for the Optik-Labor in Germany that specializes in the processing of optical components and has an excellent reputation.

Regarding Optik-Labor and their service see:


I applied the two red lines myself with a water-soluble pen to mark the upper side of the lens so that I can then reinstall it correctly


Moving on to the aperture issue




I use the toothpick to carefully loosen the stuck slats.




Oil can be seen on the aperture blades.




The “dipstick” shows that the lens is very close to the aperture.

So when cleaning with Zippo lighter fluid I have to be careful that none of it gets on the glass.

The first attempt with Zippo resulted in the shutter blades no longer moving at all. Result of cohesion.

So I have to disassemble further to get to the lever that moves the aperture blades.

Two of the bayonet screws, which are glued - as is usual with Nikon - can be loosened.






The third gives up its resistance after being heated with a cordless soldering iron.

Here I can use the soldering iron sensibly, as it has too much power for delicate electronic soldering work




Adhesive residue on the bayonet screw.

In order for the bayonet ring to be removed, the contact block must first be unscrewed.

Two screws hold it to the bayonet ring.

The contact block is connected to the tube via a ribbon cable.




Bayonet and aperture ring are off.




The aperture blades do not stop with a ball, but with a notch.




The apertures values set with the aperture ring are transferred to the aperture register via this inserted metal ring with a control cam.




The pinion that transmits the rotation of the AF motor to the focusing unit is only loosely inserted.




Applying Zippo lighter fluid to the aperture blades ...




… move through …






… and after repeating the procedure several times and carefully drying the aperture blades with the Dremel Versatip butane gas burner, the aperture snaps back into place as it should.


Assembly




The metal ring comes back into place.




In order not to have to thread the contact block through the rear cover and thus stress the ribbon cable, I unscrew it from the bayonet ring.






The bayonet ring is screwed on...

… and the contact block is back in place.




Top view from above.




The cover is installed.




Likewise the rear optical unit.




Everything works perfectly on the Nikon F5.

Here the stop down button just closes the aperture to f = 22




Almost fully operational again




A big thank you to my disposable plastic syringe, which even withstood a (minimal) filling with acetone.


Conclusion

• Unfortunately, I had bad luck with the optics and couldn't remove the clouding myself. Since it is a wide angle, the clouding in the rear optical area is already noticeable in the viewfinder. But in the Optik-Labor the cemented lens will certainly be restored to its former freshness.
• It is not necessary to remove or disassemble the aperture register to clean the aperture blades. But no matter whether cleaning is installed or removed - as long as the oily greasing of the helicoids is not replaced, the problem will come back.
• The acetone has once again demonstrated its ability to loosen presumably stuck threads. Collateral damage here is limited to a slightly damaged surface coating.
• As soon as I receive the cemented lens back from the Optik-Labor, I will continue here.

+++

All information provided without guarantee and use at your own risk.

Fantastic work Andreas. I’m still learning how to work on lenses and have limited my projects to stuff from the junk bit at the local camera shop. It had not occurred to me to mark lens surfaces to keep them oriented correctly. I have just been carefully laying them in order.

Your posts are very helpful in learning the craft of camera repair.

88E30M50 said:

Fantastic work Andreas. I’m still learning how to work on lenses and have limited my projects to stuff from the junk bit at the local camera shop. It had not occurred to me to mark lens surfaces to keep them oriented correctly. I have just been carefully laying them in order.

Your posts are very helpful in learning the craft of camera repair.

Click to expand...

Thank you!

I'm happy if my contributions help

Big thanks to the authors of the following articles who provide valuable information on servicing the Nikkor AF 20/2.8 D:

„How to disassemble and reassemble a Nikon AF 20mm 1:2.8D lens in order to clean sticky aperture blades“




[not the AF-D version]

Mine has the aperture blades stuck too. They are stuck wide open though. Nikon fixed it for me under warranty 4 years after I bought it.

Chan Tran said:

Mine has the aperture blades stuck too. They are stuck wide open though. Nikon fixed it for me under warranty 4 years after I bought it.

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Did Nikon give you any information about what caused it?

Actually it could only be oil contamination like with mine, unless the lens was damaged.

Andreas Thaler said:

Did Nikon give you any information about what caused it?

Actually it could only be oil contamination like with mine, unless the lens was damaged.

Click to expand...

No they just fixed it. Nikon tend not to tell me exactly what's wrong. I have sent cameras to them before. I bought the lens as a demo so it's cheap. $256 and with full warranty so I can't complain. My Nikon Df has an intermittently failed exposure metering system. They fixed it but said they replaced the exposure unit. Did cost me over $400 though as it also 4 years after I had it and they only warranty the camera for 1 year.