Monday, May 10, 2010

Fixing Broken Plastic Nikon F-Mounts

Introduction
There are more than a couple Nikkor lenses out there that for some reason Nikon decided to use a plastic lens mount instead of a metal mount. Models include the 18-55 DX and 55-200 DX in both non-VR and VR variants. It doesn't take much more than an accidental drop or knock and the plastic tabs will break off and the lens wont be able to mount to the camera body. Luckily this is pretty easy to fix. Searching around after doing this I found similar repair guides written up here and here.

Disclaimer
I should make a short disclaimer that performing this kind of minor surgery on your lens yourself will most likely result in any warranty you once had to be void. In addition, any damage you my cause is not my responsibility. You should take due caution to be careful to not damage your lens including covering the glass lens elements as needed.

So Here Goes

What you will need:

Spare Part
: I gave the Nikon Parts Department a call (number is at the bottom of the link btw). A friendly Nikon service rep answered the call and helped me. A few days later my part arrived at my door stop. $15 all up.

Tools: #0 and #00 Phillips head screwdriver. If you dont have these, a precision screwdriver set is readily available from Amazon for less than $10.

Optional: Second set of hands will prove helpful for the reassembly process.

The replacement F-mount is a plastic unit, just like the broken one. It has an attached cable and a thin piece of plastic that protrudes out for a few cm, make sure you note where that plastic comes from when you remove the old bayonet mount.


Figure 1. Nikon 1C999-601-2 replacement plastic bayonet mount.

Place the lens with the mount pointing up. Looking at the F-mount, you will see 3 large screws (all three visible in Figure 2). I used my #0 Philips head to remove them. I put them on a piece of paper and labeled them to make sure I remembered where they came from.


Figure 2. The old lens mount with broken tabs.

Next its time to remove the screws from the collar. Note there are two sizes here (Figure 3). I removed the medium screws with a #0 and the smaller with a #00 Philips head. Again, separating them on a labeled piece of paper makes reassembly that much easier. Admittedly if you it wouldn't be too hard to figure out where they go if you did mix them up.


Figure 3. Screws on the collar. From memory there were two medium and 3 small screws.

Now its time for the fun part. Using gentle force you can remove the center most ring. Next the tab that houses the electric contacts can be removed. It's attached to a ribbon cable so all you need to do is gently lift and remove. The tension of the cable will pull the piece downward. Let it rest inside the lens. Next is time to remove the plastic bayonet mount. This piece is attached to a small cable you will need to unscrew (#00 Philips screwdriver).


Figure 4. Removal of the plastic bayonet mount.

Unscrew the cable from the old bayonet lens mount and attach it to the replacement unit. I found that juggling the small cable (which is spring loaded), holding the bayonet and screw driver easier with a second set of hands. No doubt you could do it on your own though...


Figure 5. Transplanting the internal cable from the old mount to the new. Kudos to my mate Kevin for being the extra hands.

Once done, the new bayonet can be put in its new home. Make sure to line everything up and pay special attention to the two metal shims under the bayonet which may have moved during the surgery. They can only go one way. I used my small screwdriver to help line everything up.


Figure 6. Lining up the shims before putting the bayonet in its new home.

Once that's done, screw it in place with the large screws. Next, the tab holding the electircal contacts can be gently lifted back in place. It should lock into it's home position. The final piece to go back on the lens is the center ring. There are two ways to put this back on. First method is to put the ring back in place and use a screwdriver to push the aperture controlling tab into position (Figure 7).


Figure 7. Moving the aperture control tab with a screwdriver.

The second method is easier. Simply use the gap made for the tab on the center ring to push the aperture control tab forward as you slide and push down the whole center ring down, locking it into place. It is much easier to do, than it is for me to explain. I think Figure 8 shows the process reasonably well.


Figure 8. Second method for putting the center ring back in place.

All you need to do now is put all the screws back into the lens and you have successfully repaired your lens. After I was finished I noticed that a stray finger had made its way onto the rear glass element. A quick brush and polish with a lens pen will take care of this.


Figure 9. Finish up the repair with a good cleaning.

Put it back on your Nikon SLR camera body and enjoy the fruits of your labor!