Nikkor LTM focus adjustment - 105, 135?

[Dante_Stella]

I have a 105 and 135 Nikkor that are front focusing. A very well known repairperson (who will rename nameless - but take your three guesses) claims that they can't be adjusted.

Which is not believable, since not even Nippon Kogaku was godlike enough to machine all metal and grind all glass so perfectly. And every lens I've seen of theirs has an adjustment method.

Sooo... Does anyone have any information on how the 105's optical unit comes out? Does it just unscrew from the helilike the 135? Is it shimmed? Does the focus adjust via the grub screws on the focusing ring?

Thanks!
Dante

 

[mdarnton]

How's the RF alignment at infinity? Does it zero out perfectly? Or does it go past infinity?
Is the cam a full circle on the back of the lens, or just a narrower finger that connects only with the camera's cam follower?

 

[rfaspen]

I'm going to guess at mdarnton's gist. If the lens zero's out at infinity with the RF, but front focuses closeup, the optical unit needs to come back a tad. Right?

I guess because I have a lens doing just this 🙂 You can see I'm confused.

Sorry Dante, I don't have any Nikkor LTM so I'm in the dark on disassembly.

 

[Dante_Stella]

Off a few inches close up. Seems to be a constant error in ring rotation. Mdantsane, it's a tab cam, not a ring.

Dante

 

[enasniearth]

Nikkors

Nikkors

The only one I have had apart was a late 85/2
That was a train wreck outside
On the 85 there is a black sleeve/ tube that hold the depth of field scale .
Three small screws hold it in place ,
When you remove them the sleeve slides off the rear past the Leica thread .
There is a hole in the exposed chromed brass tube ,
You can remove the close focus stop screw and screw the helicoid apart .
The optics are removed from the front , much like the 135
Never had a 105 apart might be different .
The 85 was missing the infinity lock screw and it was assembled in properly
By someone at some point in its life .
So much for a $200 buy it now black lightweight nikkor 8.5cm f2
This is for the screwmount type , nikon mount differs .

 

[jonmanjiro]

My experience working on LTM Nikkors is that there is no way to adjust the focus by unscrewing some screws, rotating something, then retightening the screws. Assuming the RF is fine, all you can do is change the thickness of the shim between the optical cell and helical.

 

[ferider]

If the front focus is constant across the range, you can also grind the cam down.

 

[Peter Jennings]

I have a Canon 85/1.9 that was dropped at some point in its lifetime. At first i couldnt understand why it was back focussing. After tearing it down and examining closely, i noticed a very, very slight bend in the cam. The cam was slightly compressed by the drop and this was throwing off focus. I tried to bend it back into the proper shape as best i could - very gently. Of course, it was still a bit off, so i ended up applying some epoxy to the tip of the cam and filing it down slowly while checking focus every so often. It now focusses perfectly and i can hardly notice the thin film of epoxy on the cam. What I learned is that even fractions of milimeters can make big differences in focus accuracy.

 

[Peter Jennings]

On the 105, the entire optical unit simply unscrews from the body. Grip tightly and twist. There should be a brass ring between the optical unit and the body that slips off. If infinity is accurate, I don't think the problem is the brass ring. Adjusting its thickness will throw off infinity focus. Have you checked the focus accuracy via ground glass and multiple bodies?

 

[mdarnton]

If the front focus is constant across the range, you can also grind the cam down.

Exactly, which is why I am asking if it zeros out at infinity. If it doesn't then the tab is too "long", and you can take a bit off it with sandpaper. I use 400 grit wet or dry, place one piece face up on a very flat surface, another face down with the lower piece sticking out a bit. Focus so that a breath of tab is sticking out equal to the thickness of the top paper. Put the bulk of the back of the lens mount on the smooth paper, with the tab hanging out over the edge overlapping onto the grit and carefully rub the lens ONCE on the grit while using the rest of the lens on the smooth paper as a square so you don't sand crooked, then check against infinity again with the camera. Repeat until perfect, and you only get one chance--you can't put metal back on, and you will be surprised how quickly it goes away. Nothing coarser than 400-grit!

The caveats are first, you have to know, absolutely, that your camera RF is spot on. Second, the error has to be over the whole range, not just close up. Third, when the lens is set to infinity, without the RF, real lens focus needs to be accurately on infinity. Fourth, you have to be using a real infinity for these checks--for those lenses, like something no nearer than two miles away. If all of those are in order, it's the lens cam. If not, then you don't really know where the problem is, so you can't fix anything.

 

[rick oleson]

If the lens focuses correctly at infinity but not close up, the problem is not in the lens but in the rangefinder cams in the body.

 

[Dante_Stella]

It's the master focus. That much I do know, since it is the same amount of travel on the focusing ring to correct at any distance. So it's really a question of how to change the position of the whole optical unit relative to the helicoid, not grinding/adjusting the focusing cam.

 

[Peter Jennings]

Dante,
If the focus is off at all distances then the brass shim is the culprit. I recommend taking the lenses apart, cleaning them, putting them back together and then testing them again before attempting any irreversible adjustments like thinning the shim. Just out of curiosity, what camera(s) have you used to test the lens?
Good luck,

 

[mdarnton]

I guess if you have two lenses and want them both to work, then you need two bodies. . . . That's one way to sell cameras.

 

[Dante_Stella]

Nikon RF lenses were really not meant to be adjusted. Nikon's solution to finicky lenses like the 50 1.1 was to adjust the camera body, thus making them a pair.

For obvious reasons no lens should individually be adjusted to match a specific body.

There is nothing different about Nikon RF lenses. The 135 has a master shim and has a rear element that screws in/out. They are no different from 50mm Sonnars (old school) or Jupiters in that regard.

Having looked at the 135, which came back last night, this was an eminently solvable problem in one of two ways:

1. Screwing the optical unit just 100 degrees inward, which is like 1/20-1/10 of a mm (I tested this without the shim and noted the position) achieved perfect focus all along the RF range and a very, very sharp lens - particularly where you center the focus at f/4.

2. Alternatively, about 1/4 turn of the rear group fixed the problem, though the RF deviates as you approach infinity (at the hard stop, focus is perfect).

The front focus we are talking about is in the range of 3" at minimum focus, so we're not talking a huge adjustment (and it might well be good enough for film). The only thing that I can't nail down is whether the RF cam is the thing that really needs adjustment (the RF patch goes *past* infinity, but using solution #1, the rangefinder focus is 100% accurate), but someone who is motivated and has even a rudimentary tool for thinning the shim could fix this in about half an hour. Apparently my person was not the right person.

I put the lens in the classifieds, cheap. Less, I think, than I even paid for the CLA. With a heavy schedule and a house move coming, I just don't have time for stuff like this anymore (and also, I'd have to buy some tools to shave down the shim - since the emery boards I had seem to have been pilfered by household members 🙂). But someone might have fun with this. And you don't need any fixes if your plan is to use an adapter to get it onto a mirrorless.

Dante

P.S. With the 105, I just tightened the front group and it behaves as expected on an M240 and front focuses a tiny bit more on the 246.

 

[Dante_Stella]

Update. I nailed it with the 135 using a Revlon hard/soft emery board ($3.99/10 at CVS) and sealing the brass with some clear nail polish (a very, very thin coat, just as NPK did with paint long ago). Take a look at the below. How'd I do? This is minimum at f/3.5.

What I have noticed about a lot of telephoto lenses (even aside from these two) is that they are only really accurate starting at minimum focus distance plus about 10%. Small amounts of cam movement translate into large amounts of focusing movement, and you are just fighting lens mechanical slop. So your lens might be on the verge of back-focusing at the stop but showing the usual front-to-back focus shift elsewhere. Helps to have a LensAlign to check this.

At the end of the day, we do all need to bear in mind that as legendary as Nikon is, the machining of these early lenses was far from perfect - at least from the standpoint of sticking these lenses on digital M cameras with higher resolution than the films these lenses originally serviced.

Dante