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I recently bought a Nikon 35-70 mm f/2.8 lens with some scratches on the front element. I exchanged the front element with the element of an old lens I had lying around. Everything works fine, but now the lens is a tiny bit soft on the long end.

I noticed some spacer rings behind the front element. What do they do, and how can I now if the lens needs more or less of them?

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  • \$\begingroup\$ I do not think using spacers as a band-aid for a lens element that is miss aligned is the correct way to address the problem. You may need a professional repair shop for such a complex piece of equipment that requires precision on such a small scale. \$\endgroup\$
    – Alaska Man
    Commented Jul 3, 2020 at 18:50
  • \$\begingroup\$ @AlaskaMan: I don't think it is misaligned. I have two identical lenses, one in totally worn out mechanically and I dropped it, which broke it at the mount. The other is one I picked up recently for about 70 dollar, it is perfect except for 3 mayor scratches on the front element. So I exchanged the front element with scratches for an identical one from the other lens. Now I also have two sets of the spacers that Nikon originally uses to fine tune the lens. I think a solid solution is possible if I know how Nikon fine tunes their lenses. \$\endgroup\$
    – Orbit
    Commented Jul 3, 2020 at 18:57
  • \$\begingroup\$ So is the real question, "How are lenses tuned upon assembly"? \$\endgroup\$
    – mongo
    Commented Jul 7, 2020 at 11:35
  • \$\begingroup\$ @mongo: That assumes it is never done afterwards, which may be right. It would be interesting to hear from someone who has worked at a Nikon service center. \$\endgroup\$
    – Orbit
    Commented Jul 7, 2020 at 12:40
  • \$\begingroup\$ My guess is that there is an assembly guide, whether manufacture or service. There was a tech in our lab who did lens servicing, and as I recall he got copies of the vendor service guides. \$\endgroup\$
    – mongo
    Commented Jul 7, 2020 at 14:21

2 Answers 2

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It does not seem possible to use the spacer rings to adjust the lens at the long end. There are only two sets of spacer rings in the lens, one set behind the first lens group, and one set in front of the lens mount.

exploded view

The first set of spacer rings can be seen in the figure above marked with 1K160-756 to 760. It is not very easy to read, but it is the 8th item from the top left. In the figure below it is marked with number 94, the 3rd number from the top left. The second set of spacers is marked with 1K161-160 to 168 (or 178) in the figure above,and it is the 4th item from the bottom left. It is marked with 97 in the figure below, and is the 5th number from the bottom right. Item 1K161-178 is also marked as 97 below, but I haven't found it in the figure above yet. Under the pictures is a copy of the page from the parts list where they are listed.

Tech. drawing

part list

Here are some links that I found very useful on how to clean/repair this lens: Mikeno62 at Youtube. Please give this guy a thumbs up if you like the video, I think it is very well deserved.
https://www.youtube.com/watch?v=o6dB0cCzYBE&t=1191s

DIY extravaganza on Youtube, also great work:
https://www.youtube.com/watch?v=0v2XZHtkLVQ&t=631s

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A camera lens is a complex array of lens elements. Some are cemented together, some are air-spaced. Believe it or not, the air-space, being lens shaped, acts as an element. Changing the air-space thickness tweaks the focal length. Odds are, the scratches on the front element, had little effect on lens performance. The lens you substituted likely will degrade. Changes of improvement are low.

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  • \$\begingroup\$ You could very well be right. It may be a bit stupid, but I really don't like huge scratches on the front element. I guess I am not the only one though, considering that I picked the lens up for about 70 dollar, while it usually goes for 3 to 5 hundred. \$\endgroup\$
    – Orbit
    Commented Jul 8, 2020 at 20:02

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