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Chipping a Nikkor - A Walk-through

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Bjørn Rørslett:
[Posted 24 March 2010:  Article and image copyright Bjørn Rørslett ]

This is a short illustration of the process of CPU-converting ("chipping") a Nikkor lens. The example is the 18 mm f/3.5 Nikkor AIS. The 18 mm is not a very difficult lens to modify, but it does demonstrate some of the minor niggles often encountered when you set out to implant a CPU. Let's remember that these lenses never were designated to receive an internal CPU, so that it usually is possible might come as a surprise.

The first step is assembling the pieces.

Here is the lens, together with the CPU print, 5 signal pins, and the contact block.

Assembling the contact block is not rocket science, more like playing with Lego bricks.

Bjørn Rørslett:
Here I have removed the rear light baffle (always black, it usually is secured by 3 small screws). We're looking straight into the internals of the lens, and immediately note two problem areas.

1. There is not sufficient space for the contact block, so material must be removed from inside of the bayonet mount.

2. The aperture coupling slider has two screws the heads of which potentially will interfere with the print. These heads need to be sanded down to be flush against the surface of the slider. An easy task suitable for any keen Dremel user.

Bjørn Rørslett:
Now, time to drill the two holes for the retaining screws for the contact block. An 1.25(-1.5) mm bit is suitable. I frequently use a jig so it's easy to drill the holes in a correct position. Pin number 4 of the block has to line up precisely with the centre of the topmost bayonet screw (the one adjacent the the index mark on the lens). This correct position will be evident on the next pictures.

After drilling, the holes must be countersunk so the screws come flush to the surface. Otherwise, the lens will jam when it is attached to the camera. The material of the mount rim must be thinned on the inside, if necessary, to keep its thickness to 0.8-0.9 mm in the area where the contact block is to be inserted. Older lenses may have the required thickness already, whilst most AIS lenses need to be trimmed. Only do the removal of material on the inside of the mount.

Here is the contact block in the correct orientation, and it's easy to see that we now have plenty of space for it in the bayonet mount. The mount has been trimmed on the inside to give the appropriate thickness (0.8-0.9mm) as well.

The contact block, with the CPU print, is put into its place and secured by the retaining screws.

Bjørn Rørslett:
Now, the bayonet is put back onto the lens and the print dressed so it doesn't snag on any moving parts inside. It's beneficial to make a paper dummy if the placement of the print is deemed difficult. The print is fairly delicate and should not be bent back and forth excessively.

Make a cut-out in the rear light baffle to accomodate the contact block, and fasten the baffle with at least 2 screws. Sometimes, the locking screw of the mount is one of these and this has always to be present. In the case of the 18 mm, we managed to save all three holes, so all three screws can be used (and the locking screw didn't need to be touched at all). This will vary from lens to lens, though.

Bjørn Rørslett:
Here is the completed and rejuvenated 18 mm f/3.5 S Ai-P lens. It is now compatible with each and every Nikon "F" mount camera ever made, and will meter on all of them. You can dial in the apertures from the camera, or use the aperture ring (if the camera allows this operational mode). All metering modes are available, and you can use exposure program modes A, M, P, and S.

(by the way, all illustrations are hand-held snapshots with the D3S/125 APO-Lanthar, 12800 ISO).

That's all, folks !!

(note to self: dust off lens before taking the product shots. The CV 125 APO is darned sharp so all dust specks are mercilessly shown. And let Erik drill the mounting holes, he does a much neater job than me :D )


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