Nikkor 24-120/3.5~5.6 AF-D (IF): Fungus removed, assembling the rear lens block, infinity focus stop

Andreas Thaler · Dec 21, 2024

Andreas Thaler said:
To what extent is the viewfinder image useful in assessing the centering of a lens?

In the viewfinder of my Nikon F4E I only see a very slight blur in the top right corner at the maximum zoom position.

This is an application for the Nikon DW-21 6 x High Magnification Finder!

I have to try it out on the F4E tomorrow.

Andreas Thaler · Dec 21, 2024

But if I imagine that I mount the zoom lens on the camera, see blurring, take it off, dismantle the bayonet, adjust the position of the rear lens block, take into account the mirror image in the DW-21 viewfinder, mount the bayonet again, put the lens on the camera, check the image in the viewfinder, take it off again, dismantle the bayonet ...

I can spend the day there.

forest bagger · Dec 21, 2024

Of course that works only on lenses which have a rear lens block that has to be centered, Andreas.
Which lenses, you can see when the lens block is mounted with three screws for which the lens block has bigger holes for the shaft of the screws than needed.

Andreas Thaler · Dec 22, 2024

Andreas Thaler said:
This is an application for the Nikon DW-21 6 x High Magnification Finder!

I have to try it out on the F4E tomorrow.

I tested the zoom with the DW-21 on the Nikon F4 and other Nikons, i.e. assessed the viewfinder image. I cannot detect any significant blurring, at least not at the maximum zoom position.

But when the zoom ring stops, the infinity focus for the whole image no longer works properly, regardless of whether AF or MF.

I don't think I can improve this, because I would have to adjust the focus stop and I don't see how I can do that.

But I will check the position of the wiper contact for the AF in the tube. Even if that won't change the focus stop (mechanically).

Otherwise the limitation remains that I move the zoom ring to the end position 99.9%.

Michael @forest bagger, I'm not asking whether I was just lucky when installing the rear lens block, or whether it really is just a matter of not attaching the lens block at an angle.

Everything there except the shim and the screws is made of plastic and doesn't give me the impression that it offers any special horizontal adjustment options.

In the last picture below you can even see a recess for the screw head on the rear lens mount.

This means that moving the rear lens mount is not intended for horizontally adjustment?

The plastic makes sense for vertical correction, as adjustments can be made in three places by tightening the screws to different degrees. The plastic does give a little.

See pictures:

So my approach of marking the screw head positions was probably the right one.

forest bagger · Dec 22, 2024

Andreas Thaler said:
In the last picture below you can even see a recess for the screw head on the rear lens mount.
This means that moving the rear lens mount is not intended for horizontally adjustment?

I think you are right, in this case.

Andreas Thaler said:
The plastic makes sense for vertical correction, as adjustments can be made in three places by tightening the screws to different degrees. The plastic does give a little.

No, that is a fallacy.
The vertical correction is done by the thicknes and sometimes the number of the shims made of brass.

Andreas Thaler · Dec 22, 2024

I worked on the zoom again today

I no longer attribute the problem with the blurring at maximum zoom position to a problem with the sliding contact in the tube, but to the infinity stop that is set too close.

I'm currently looking through the service manual to see where I can adjust this, probably from the outside under the rubber coating of the focus ring.

I couldn't see any mold in the rear lenses after disassembling them and to be on the safe side I reset the wiper above the sliding contact in the minimum zoom position. But as I said, that didn't change the focus problem.

Andreas Thaler · Dec 22, 2024

Underneath the rubber covering of the focus ring are two pairs of screws that connect the focus ring to two sliders.

These sliders are coupled to the second lens group, which is moved back and forth to focus.

A plastic plain bearing holds the respective slide in the tube (arrow).

This sliding bearing is missing on the second slider. I suspect that it fell into the tube, which also explains the clicking noise when I shake the lens.

There are also deep scratches on the outside of the tube. Something must have rubbed here when the tube was extended during zooming.

This is where my repair attempt ends

I couldn't change the focus stop; to do that I would have to take the zoom apart further. And I couldn't figure out where to set it on this lens.

Taking a zoom apart in an ordered sequence is a tough job.

There are no step-by-step instructions in the service manuals which provide a detailed tutorial, screws in plain bearings are often stuck, and grease and oil can quickly get on your hands.

Putting it back together including doing all the required documention beforehand is something for dedicated specialists.

Anyway, I don't enjoy this lens in this scratched state and don't want to take photos with it.

But it's a nice exercise in taking it apart intuitively and to obtain small parts, especially plain bearings and screws:

The large spiral spring at the top assisted in moving the zoom mechanism inside the tube.

A cleaning bath in isopropyl alcohol removes grease and oil.

Andreas Thaler · Dec 22, 2024

Even the repair startet well but was finally not successful, I was still able to learn something new.

And, as always, it was fun

+++

All information provided without guarantee and use at your own risk.

forest bagger · Dec 23, 2024

Hello Andreas,
as I had to stop several attempts to repair some old zoom lenses due to unforeseeable time expenditure or lacking spare parts in the last five years,
I have a few boxes full of spare parts that I will hardly use anymore.
Are you interested in these?

Andreas Thaler · Dec 23, 2024

forest bagger said:
Hello Andreas,
as I had to stop several attempts to repair some old zoom lenses due to unforeseeable time expenditure or lacking spare parts in the last five years,
I have a few boxes full of spare parts that I will hardly use anymore.
Are you interested in these?

Thank you Michael for the offer!

In my experience, zooms lenses are very difficult to repair, especially disassembling, assembling and adjusting them is very demanding.

I therefore try to only do work that has a chance of success, such as cleaning oily aperture blades or dirty lenses. Everything else is an adventure.

Although sometimes I have had success, I prefer not to do it.

Therefore, I am probably not the right person for your offer

Andreas Thaler · Dec 23, 2024

@forest bagger

Michael, since you have a lot of experience with the repair of Nikkor zoom lenses in particular, wouldn't you like to write a post about it?

General advice, perhaps an example?

I think that would be of interest to many readers.

I only know of repair reports that go into detail on this topic from Richard Haw:

Lens Repair & Review Articles

Lens Repair Articles: Here’s the core the entire site. I intend to have the most comprehensive database for everything related to the repair of classic Nikkors. As of today, I believe that th…

richardhaw.com

forest bagger · Dec 23, 2024

Hello Andreas,

my problem with such advice posts is that I have so many things to do (besides the still continuing repair work) that I can't afford the time for this.

forest bagger · Dec 23, 2024

Andreas Thaler said:
Therefore, I am probably not the right person for your offer

It looks like my collected old parts, which now fill over 50 boxes, will end up in the bulky waste when I die.

Andreas Thaler · Dec 23, 2024

forest bagger said:
It looks like my collected old parts, which now fill over 50 boxes, will end up in the bulky waste when I die.

You could sell them as bundles on eBay.

That's always in demand.

Andreas Thaler · Dec 23, 2024

forest bagger said:
Hello Andreas,

my problem with such advice posts is that I have so many things to do (besides the still continuing repair work) that I can't afford the time for this.

But your knowledge is indispensable!

Do you want to write it together?

The ghostwriter from Vienna is always looking for meaningful projects

Andreas Thaler · Dec 24, 2024

Is it possible that this newer generation of lenses with a large proportion of plastic was no longer designed for repair and service?

I saw a pressed front lens in a plastic frame on this zoom that cannot be opened. The retaining screws for the tube are deep inside and are secured with paint. I only reached the focusing mechanism (whose stop I wanted to adjust) after taking it deeply apart.

All of this does not look as if it was designed for service work.

Perhaps lenses with manufacturing defects such as decentering were completely replaced by Nikon within the warranty period?

I experienced this with a newer Canon EF zoom with decentering.

forest bagger · Dec 24, 2024

Andreas Thaler said:
Perhaps lenses with manufacturing defects such as decentering were completely replaced by Nikon within the warranty period?

Maybe that counted for cheap lenses - expensive ones were repaired.
But the front lenses pressed in plastic have to be replaced as a whole according to Nikon - only I cut them apart and clean the inner surfaces...

Andreas Thaler · Dec 24, 2024

forest bagger said:
But the front lenses pressed in plastic have to be replaced as a whole according to Nikon - only I cut them apart and clean the inner surfaces...

You should apply for a patent for this!

Andreas Thaler · Dec 24, 2024

forest bagger said:
Maybe that counted for cheap lenses - expensive ones were repaired.

Richard Haw shows how the old metal Nikkor zooms can be dismantled and reassembled.

That's your specialty too

Working with nested tubes and rings that way always reminds me of psychological tests where you have to move three-dimensional figures in space to form predetermined features

It's also oily, you have to set meticulously marks and the slotted screws in the bearings are stuck from time to time.

That's only for the completely intrepid.

Repair: Zoom-Nikkor 100-300mm f/5.6 Ai-S

Hello, everybody! It is beginning to get cold here and it’s now time to shoot pictures of migratory birds. Birding has never been my thing because of its high-cost in terms of equipment, it&#…

richardhaw.com

forest bagger · Dec 24, 2024

Oh yes, in 1990 I owned this 100-300/5.6 AI-S Nikkor and tried to use it for taking pictures in the forest with my Nikon F3 HP.
Although I used a Kodachrome 400 film, held the lens firmly pressed to a tree and stopped breathing during the 1/30s exposure time the pictures were all blurred...

Today I could use this lens on a Nikon Z6 with built-in anti-shake and up to 256.000 ISO - if I had kept it.

ic-racer · Dec 24, 2024

Never was a fan of zooms. For 30 years I used the Zeiss Rollei 35mm system which did not include any zooms.

I did repair my Bolex Switar EE zoom 20 years ago. The EE aperture blades needed to be re-set but didn't touch the optics. Still going strong on zinc cells today.

Andreas Thaler · Dec 24, 2024

forest bagger said:
Oh yes, in 1990 I owned this 100-300/5.6 AI-S Nikkor and tried to use it for taking pictures in the forest with my Nikon F3 HP.
Although I used a Kodachrome 400 film, held the lens firmly pressed to a tree and stopped breathing during the 1/30s exposure time the pictures were all blurred...

Today I could use this lens on a Nikon Z6 with built-in anti-shake and up to 256.000 ISO - if I had kept it.

Of course, I own the 100-300 as an addict and was able to take sharp photos with it on the Nikon F3.

However, it does stand out on the street, especially in uncertain times like these ...

Nikkor 24-120/3.5~5.6 AF-D (IF): Fungus removed, assembling the rear lens block, infinity focus stop

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