A little technology

Repair is a profession...

It's also a passion

The purpose of this short article is to show that...

An exceptional case

Nikkor 105mm f/1.8 AIs... Massacre and rescue!

Part 1

I was given this lens for a problem with a focusing ring stuck at mid-distance and fungus.

These problems are common for equipment that has not been used for a long time and/or has been poorly stored.

In principle, these are relatively simple and usual interventions. To the great despair of the medical team, the case was much more serious…

This lens had a little visible ding on the lens hood, but nothing to worry about.

Knowing how this optic is constructed, I started by removing the rubber ring.

Behind, there is a tape which holds the distance ring, the focus ring and the identification ring.
This tape was no longer original… This is not a good sign!!!
Removing the front filter holder ring was not easy, it came with the entire sun visor, a result of the impact.
The optical unit, the rear mount, the aperture ring and its guide, the rear finishing ring and the chrome have been removed.
At the first attempt to rotate the rings, the front helical (the one which supports the optical group) separated from the barrel.
The reality is that this optic had been dismantled (no screws tightened) without removing the two linear guides, which represents an impossibility of reassembly, it was therefore incomplete.
But that’s not all…
Removal of the two linear guides, everything is completely blocked. ?
In fact, this optic had received a violent shock and the whole thing was ovalized.
Forcefully, I removed the focus ring from the barrel, degreased everything well and measured the diameters of the rings with a caliper.
Some 1/10 of a millimeter difference…
By hand, I gradually tried to straighten, but the rings were still in forced rotation with hard points.
Some professional contacts from an Anglo-Saxon group to which I exposed these problems advised me to use polishing paste and to calmly break in the helical ramps to catch the sails.
I had a mediocre paste available, which mixed with oil was very helpful.
A full Sunday of screwing, unscrewing, cleaning, testing, screwing and unscrewing, again and again, to the point where it borders on tendinitis in the wrists! ?. It’s really unpleasant and dirty work.
After a few hours, there was a clear improvement, the roughened rings are still far from perfect.
To refine it, I ordered pastes (for lapping the valves) which are in two densities.
Since the dismantling of these ramps could not be done logically, I had no positioning reference. little by little with numerous attempts, I found the right positions and made the essential separation marks.
But the worst was to come…
The diaphragm presented a malfunction, one of the blades was not in place and during movement, this blade forced on the others by lifting them at the risk of twisting them.
The aperture block had been dismantled (broken varnish on the screws) and the rotating part which guides the slats, tinkered with “roughly”?
This tinkering had widened one of the guides and the slat could no longer position itself more normally…
As much as the ramps can be improved, the diaphragm requires changing the part, certainly not found.

Part 2

Break-in and obstinacy are the breasts of this repair…

The valve lapping pastes have arrived, “action!”

Two types of grits, I used the finer one.
Break-in, cleaning, polishing, test reassembly, several times.
Lubrication and partial reassembly.

Partial, because the diaphragm block was removed while awaiting a solution, and no screw was fully tightened or secured with varnish.
Reassemble the optical unit and test, it works…

In all sincerity, the challenge is of course exciting!
But if we take into account the time spent, the products used, the current impossibility of having a functional aperture and so on, compared to the price of a great opportunity, is the stake worth the Nikkor.

However, if I find a part for the aperture, which seems very unlikely, I will go all the way!

Part 3

The diaph, “mission impossible?” Not sure!

I’m always very bitter when a Nikkor seems completely beyond repair due to lack of parts.
Why not a repair that “doesn’t try anything…”

I took an impression with two-component silicone resin of the locations in good condition.

By pressure, this resin exceeds these locations a little in thickness, which will leave space available for the movement of the lamella pin.

A little adjustment with the cutter on this impression so that the part to be repaired takes place correctly.

The damaged part has been enlarged so that the repair is more resistant.
Slow curing resin was used in the restoration locations only on the upper side, because the lower side, in contact with the shaft and the lamellae, cannot have any extra thickness.

Sanding and polishing as a finish before doing a first test…

It works, but still requires some adjustments.

Of course, in its raw state it’s not very elegant, a coat of matte black Rewell spray paint is a cover-up.

The resistance to use remains to be proven, but this part supports little mechanical stress, apart from its rotation, that is reassuring!

Finally, taking into account the movement of the pin of the lamella in the resin and in order to soften the possible friction, I added a little dry lubricant based on graphite powder.

I decline all responsibility if you damage your toys… There are also professionals to do this work.

You can watch detailed tutorials on the YouTube channel

Nothing is totally impossible