Repair Nikkor-S 35mm f2.8 Non AI Lens

Set the lens to infinity. As you work on the lens at the initial stages make sure that the infinity position is retained. Like many old lenses you will most likely find the lens comes to infinity just at the start of the infinity mark and focuses slightly past infinity.

This is quite common – the manufacturers built in an allowance for glass expansion.

Remove the 3 small screws from around the lens focus barrel. These can be very well stuck down. Try to avoid using acetone for these as it will remove the painted finish. Dab with Isoprop and give the Isoprop at least 15 minutes to get to work.

A correctly sized screwdriver will help you avoid damaging the screw heads.

The focus barrel will now pull free from the lens. It may need a little twist to remove it. This particular lens had hardened dried grease behind the focus barrel making it harder than expected to extract.

If you twist it try to reestablish where infinity focus was by aligning the screw holes in the focus barrel with the main body of the lens.

Use a lens spanner to remove the front optical unit. This will have slots to extract this.

Here is the front optical group removed from the lens.

Remove this set-screw from the front barrel/filter ring.

The front barrel unscrews from the lens. This is one of the unusual features of this lens. Almost all parts are screwed together rather than simple press fit with retaining screws.

Make a note as you unscrew the barrel that there will be a dimple which the set-screw was located to.

The front barrel/filter ring has now been removed. You can see the location of the small dimple as indicated where the front barrel set screw located.

Remove the screws at the rear of the lens thats secure the mount plate. These are almost always hard to extract. Nikon will have used a lot of thread-lock here but you can use acetone CAREFULLY or the top if a soldering iron on these screws. A correctly sized screwdriver is essential here – we strongly recommend the specialised driver tip sold by Polar Bear Cameras to avoid chewing the screw heads up.

As the mount plate comes away take note of the forks on the rear of the mount plate and how they locate to the small tab on the lens diaphragm assembly.

There is no value in disassembling the mount assembly. If you are forced to do it for any reason beware – there are an awful lot of ball bearings which provide the aperture stop down mechanism with a frictionless feel.

Depending on the lens there may be screws retaining the core of the lens comprising the diaphragm and rear group assembly. It is possible these are absent. Older Nikon lenses are quite often slightly different internally and often show signs of extra drilling or cutting done by the factory.

If screws are present to retain the lens core assembly remove them.

This lens lacked the retaining screws and instead simply had a locating screw that aligned with a slot. The lens core can simple be pulled free.

The whole assembly is simply held in place by the front optical unit on this lens.

Here is the core part of the lens removed. It shows no grub screw fixing points so I imagine the factory had simply not fitted them for some reason.

The core part contains the diaphragm assembly and the rear optical group.

Measure the gap between the index barrel and the aperture control ring. I normally use the tip of a screwdriver to gauge the distance and make a note.

Remove this screw from the index barrel and remove.

The index barrel will simply pull free from the lens body. It may be a bit stiff due to dirt being trapped underneath.

Scribe a small mark as to where the aperture ring is fitted. This will be useful later to establish its position.

Remove this screw from the aperture ring. This screw locates to the aperture ring inside the lens which controls the aperture. You will see this in the next few steps.

The aperture ring unscrews from the lens body, unlike many lenses it does not simply pull free. You may find it is very stiff in its threads.

With the lens still at infinity from the start of the work. The inner helicoil is scribed along the stop plate to indicate its infinity position – the red dotted line indicates where to mark as the scribe mark doesn’t show well on a photograph.
Also create a mark on both the inner and helicoil to show where infinity was reached.

Marking the infinity position is really critical.

With the inner helicoil marked the outer helicoil position has to be checked. You can do this by marking the barrel and the inner helicoil with a mark indicating infinity. Also measure the gap between the outer helicoil and the lens body.

NOTE THE ORIENTATION OF THE HELICOIL KEY

With the focusing helicoils marked up and measured its time to remove them from the lens. You will need to remove the two screws that retain the helicoil key.

These can be very tough to extract and usually you will need to be able to apply some heat using the tip of a soldering iron. You need to be careful as the key itself is sometimes plastic.

With the helicoil key retaining screws removed wind the lens focus out using the outer helicoil and extract the key from inside the lens body.

With the helicoil key removed simply unscrew the outer helicoil but make sure you mark the point at which the helicoil separates.
I usually mark each helicoil with a > and < to indicate the point at which the thread separated. It’s essential with this lens to get the right thread entry points to avoid headaches during rebuild.

With the outer helicoil out of the body remove the stop plate on top of the outer helicoil.

With the stop plate removed the inner helicoil can be unscrewed. Once again make sure you mark the helicoils with the separation point.

The internal aperture control actuator is retained by a thread.

Mark the internal aperture ring position inside the lens body

This ring can now be unscrewed and its threads cleaned.

Heres the aperture control actuator now removed from the lens body.

The inner aperture ring is given a light lubrication using Polar Bear Camera Grease (Type BC-13A).

Lubrication needs to be very light here.

And now the internal aperture control ring is replaced. Positioning of this ring is critical and the following images will show you how this needs to be aligned.

Apply a light coat of lubricant (this is the same BC-13A lubricant) to the aperture ring threads. Note the small metal tab which provides the click stops for the aperture ring. If the aperture stops are not ‘clicky’ enough you can gently bend the tab out slightly to give a more positive click.

Replace the aperture ring after giving the rings threads and detents for the click stops a light dose of lubrication using the BC-13A grease.

This screws on and may be very tight at the start of the thread as the tab which provides the click stops may be pressing against it.

Here the silver barrel ring with the index scale has been applied so that the gap between the aperture ring and the barrel index can be checked and adjusted if need be.

The aperture ring needs to align well with the index ring barrel without too much gap but it also needs to align with the inner ring which will be next to check.

The aperture ring needs to align so that the small screw on the outside of the aperture ring fits between the slot in the body and the small slot on the internal aperture ring.

I use a cocktail stick to get alignment correct.

Replace the screw in the aperture ring. Do not tighten this down just yet. You may need to make changes.

Once you are happy you can tighten but be careful – the threads in the aperture ring are very fine and the ring is a light alloy – you can strip threads easily here so go careful. At the end of the process return and apply some thread-lock to this screw.

With the aperture ring assembly done check that the ring moves easily with the required click as it runs through its stops.

Replace the helicoil key into position making sure it is orientated correctly.

The outer helicoil is now lubricated using a sable brush to apply some lubricant. For this lens I am using the same BC-13A lubricant which will give a very light feel. If you prefer a stiffer feel then Helimax XP is a suitable alternative.

You should add a very thin layer of grease to the receiving threads on the lens body as well. Wipe off any excess.

The outer helicoil is now replaced. You can see in his picture the thread entry point markings of > and < together with the line which indicates infinity focus position. The gap between the helicoil and the lens body is also checked to confirm positioning is correct.

The inner helicoil is now lubricated using the same BC-13A grease as before. Dont over apply the grease as it will cause the focus to be excessively stiff. Getting the ‘feel’ right can take a bit of time but comes with practice.

Add some grease to the receiving threads in the outer helicoil and wipe off any excess

The inner helicoil is now replaced using the same approach as the outer helicoil – eg using the thread entry point marks and a mark to indicate infinity. These don’t show well in photographs. The scribe mark along the stop plate is checked to confirm positioning.

The helicoil key retaining screws are now replaced. If all of the alignments are correct with respect to the helicoils the screw holes for the key will be in a perfect position.

Replace the stop block onto the outer helicoil. Be careful it has a top and bottom side. The top side has a rebate to allow the screws to be flush.

As a note this is good practice for tightening screws inside lenses. You need no more force than you can apply using thumb and forefinger – this will avoid stripped screws threads which are often in thin and light alloys.

Now you can repair Nikkor-s 35mm lenses it’s time to start remounting the optical parts – Before you do you should quickly test the focus throw by turning the outer helicoil.

If all is correct the lens helicoils will move smoothly and will impact the stop block at infinity AND at minimum focus distance.

Insert the diaphragm and rear optical element core part of the lens – note that the screw at the base of the diaphragm unit must engage with the forks of the inner aperture control ring – see below.

You can see in this picture that the small screw on the rear of the diaphragm assembly has located correctly between the forks of the inner aperture control ring.

The screw has located correctly into the aperture control forks but the screw to the top is out of line – thats not an issue – simply rotate the lens core with the diaphragm until it aligns and then push down – see below.

The diaphragm and lens core are now seated correctly.

If the core did have retaining screws (this one didn’t) replace them now.

Replace the lens mount make sure the forks on the lens mount locate over the small tab on the rear of the diaphragm.

A handy tip here is to set the aperture ring to f16 and then rotate the lens mount around, watch the diaphragm as you rotate the lens mount. At the correct position the diaphragm will close to f16 and the screw holes will be correctly located.

Replace the screws but do not over-tighten in case you need to re-do the lens.

Replace the index sleeve and secure with the three small screws. You will need to locate the holes in the lens body.

Normally I only apply a single screw until I am happy that the lens is fully working after a test.

Replace the filter ring barrel, this screws on. Screw it down until the screw-hole is positioned above the small dimple in the inner helicoil.

Replace the small setscrew.

Replace the front optical unit…

…and tighten down with a lens spanner.

On this lens the only thing holding the entire optical and diaphragm assembly in place is the front optical block. Ensure this is suitably secure but do not over-tighten.

Align the infinity point on the focus barrel and replace the barrel into the lens. Locate the three screw-holes and replace the three small fixing screws.

I normally only apply a single screw until I am happy the lens is working as expected.

With the lens fully rebuilt check that infinity focus is correct, that the focus throw runs from infinity to minimum distance smoothly and that the aperture control and stop down are all working correctly.

Once you are happy replace any screws – if like me you left a few out pending testing – and then tighten all screws using a small dab of thread-lock .