Repair: Auto-Nikkor-P.C. 105mm f/2.5

Oh, the seasons are changing. We are now entering mid-Spring and the weather here in Tokyo is beginning to get warmer and more humid but it is still relatively cool specially if you compare it to the punishingly hot summers here in Tokyo. This transitional weather is making me sick and I have another gout attack again so quality of life has gone down a bit. Speaking of transitional, I am going to show you a very important transitional lens in this week’s article so please stay and read along.


We re going to continue with our series on the 105/2.5 family of lenses and the next one’s the successor to the previous one that we discussed last month. This one came with new coatings and hence it’s called Auto-Nikkor-P.C. 105mm f/2.5! The “C” stands for “coated” so Nikon’s marketing is simply reminding you that this lens is different and that you should buy it in case your lens is not coated. Sarcasm aside, this is an awesome lens and I shoot with this lens quite often because of the unique look that it gives to my pictures.

IMG_2369This lens came to me in a rough state but the glass was clean so I did not bother to open the objective up to clean it as it would be pointless. Looks like a pro used this lens as you can see from the wear but that is no problem at all, in fact the wear made it unique.

FullSizeRender 13.jpgThis lens sits between the original silver-nosed look and the modern rubber-gripped type so I will consider this design to be transitional. The change from it’s predecessor isn’t just cosmetic because this lens has a different optical formula! Whilst the original formula of the Auto-Nikkor-P 105mm f/2.5 consisted of 5/3 (5 elements in 3 groups) and is a Sonnar-type lens, this one has a completely new optical formula of 5/4 and is of the Xenotar-type design but is more commonly known as the “(double) Gauss-type” by collectors. The lens was perfected by no other than Wakimoto Zenji’s prodigy in order to focus closer and to have a flatter field that is much more suitable for portraiture as Nikon found that more photographers are using this lens for that purpose. In my style of shooting this difference doesn’t mean much but I can see the differences between the 2 if I look for it. I will make a separate article on this when I have the time.

sonnarGauss.pngI was starting to get worried that all this talk about groups and elements may confuse my readers who aren’t familiar with these technical terms so I prepared a simple illustration to help you visualise what groups and elements mean. A group is simply a collection or a lens element that is considered a single unit and an element is an individual lens. See the image above, it shows what is exactly different between the Sonnar and Gauss versions. I personally prefer the Sonnar’s rendering but this is subjective and very personal.

IMG_4191Here are the 2 versions beside each other. Externally, you can easily discern between the 2 by the size of the rear element. Keen-eyed readers will also notice that the colour of the coatings are different on the Gauss version, this one has a later coating technology.

Going back to the barrel’s design, Nikon made it sure that the refresh in design will also be functionally better than the older one by making the front barrel black. The older one has a silver front barrel and some people claim that the reflections from the shiny metal barrel and threads contribute to image degradation so it had to go away. Also of interest is that the focusing ring has been broadened to allow for easier focusing especially when you are wearing gloves. All these changes gave it a modern look while still retaining the robustness of the all-metal construction. This lens can stand plenty of abuse!

IMG_2363This particular lens came with an Ai ring. It originally came with a non-Ai aperture ring, I suspect that the owner had this modified at Nikon. Having the Ai update makes things much more simple because you can use this with modern cameras with the Ai-coupling tab and it will meter properly in the M and A modes. Very handy!

(Click images to enlarge)

As you can see from the images above, the lens is superb for portraiture the rendering is exquisite with the smooth backgrounds and sharp details where in-focus. The lens is also not clinically sharp as macro lenses so imperfections on the skin aren’t made prominent in the resulting pictures. Just like the Sonnar version of this lens family, this lens also has the amazing ability of rendering smooth backgrounds even if the subject is far from the nearer distances and this makes it even more suitable for use with full-body shots and as a lens for general photography. If you know what you are doing, then the potential of this lens is near limitless. Always know your gear to know when to use it or not to use it.

Please don’t share the pictures of my Thai and Laotian friends because I don’t have their permission for publishing their pictures and I do not want to get into trouble. I share this to you at great risk to our friendship because I really wanted to show you how good this lens is for portraits and how they make pretty ladies look even prettier.

OK, that is enough history lesson for today and let us begin with the lens teardown!

Before We Begin:

If this is the first attempt at opening a lens then I suggest that you read my previous posts regarding screws & driversgrease and other things. Also read regarding the tools that you will need in order to fix your Nikkors.

I highly suggest that you read these primers before you begin (for beginners):

Reading these primers should lessen the chance of ruining your lens if you are a beginner. Also before opening up any lens, always look for other people who have done so in Youtube and the internet. Information is scarce, vague and scattered (that is why I started this) but you can still find some information if you search carefully.

I highly recommend that you also read my working with helicoids post because this is very important and getting it wrong can ruin your day. If I can force you to read this, I would. It is that important!

For more advanced topics, you can read my fungus removal post as a start. This post has a lot of useful information here and there and it will be beneficial for you to read this.

About Me:

I am a photographer based in Tokyo who scours the junk section of the camera shops here on a regular basis. I started this hobby of fixing old lenses and cameras because I kept on getting scammed before when I purchase online. This turned out to be a blessing because I now buy junk lenses for a fraction of the price and then fix them to add to my growing now collection. This allowed me to buy gear that were otherwise off-limits to me if I were to get them in better condition.

I was a scale modeller before who built models for other collectors for a very longtime, got an education as a dental prosthodontist (but didn’t pursue dentistry) and growing up in a watch repair shop gave me the useful skills that would help me in this craft. Fixing my car also contributed some know-how.

Having mentioned the above, I will tell you now that I am not a professional repairman! So please take what I do with a grain of salt and I will never be held responsible for anything wrong that will happen to you and your project. I hope that the pros would guide and teach us but nobody is writing anything.

As my collection of repair notes grew, I get requests from people with similar interests and from professionals who just needed some notes just in case. Now, I am sharing my library with you for your entertainment and reference. I hope that you find my work useful.

Dismantling (Lens Barrel):

The lens barrel has a different construction from the Auto-Nikkor-P 105mm f/2.5 lens but the construction is basic enough so you will find that many things are familiar to you. I’ll not talk about the objective this time because I didn’t have to clean mine so you will have to refer to the blog post on the next version of this lens or that of it’s predecessor  for an idea on how to work with the objective.

The lens itself isn’t difficult to disassemble to its basic parts if you have the basic skills for this as well as the proper tools needed for each task. I would like to warn you that in this particular period in Nikon’s lens manufacturing history, Nikon went crazy with it’s use of glue so you will need plenty of solvents for this lens and use stronger versions if needed just to make sure it does the job. Nikon even used some kind of epoxy in this era for some of the screws (usually just 1) in the bayonet and the helicoid keys of the larger lenses. You can smell peanut butter when you heat the screws and that smell can only come from an epoxy-like material of the A+B variant. I know, my nose is sensitive.

IMG_2370Start with removing this set screw. This little set screw makes sure that the front collar of the focusing ring stays put. Be careful NOT to lose it and remember where it was screwed into position when you put it back, there should be a depression on the other side of the screw in which it sinks into. If you got that wrong then your focusing will feel rough.

IMG_2371Here is the front collar. Simply unscrew it from the focusing ring (counter clock-wise).

IMG_2372You can now access another set screw. This time, it secures the front barrel. Again, do not forget about the depression for this screw. This is even smaller and easier to misplace!

IMG_2373The front ring screws off just like this. At this point, the objective is loose and it can drop to the floor easily because of it’s weight alone so be careful and never point this down!

IMG_2374The objective can now be pulled away from the lens barrel. This part can easily roll of the edge of a table so be careful and store it somewhere safe. Never store the objective facing up or down with either end facing anything. The glass is exposed and you do not want to scratch it. I store these on their side and secured by 2 heavy things on both sides.

IMG_2375Time to work on the other end of the lens! Carefully remove these screws from the base of the lens mount. Make sure you use the correct screwdriver for this and if you have not read my write-up on screws, please do so now and this link will take you there. READ IT!

The screws look scarred and it can only mean one thing – somebody was here!

IMG_2376Once the screws are gone, you can pull the bayonet mount off from the lens but be aware that there is a spring connected to the lens barrel and be careful not to damage this part by pulling the bayonet plate too far. An overstretched spring holds no tension! Carefully use a pair of tweezers to remove the spring from either end and store it somewhere safe.

IMG_2377The aperture ring can now be removed. Nothing is screwed into it so it’s safe to pull this out from the lens itself. Notice the gunk underneath it, yuck!

IMG_2378Let’s go back to the front! We need to remove these screws from the focusing ring but be sure note their original orientation first by scratching a mark first so that you will have a reference point to come back to because this is a precision adjustment point. These hold down the focusing ring when tightened but you can shift the focusing ring 1mm to 2mm on either side and it let’s you adjust your infinity focusing. You will have to calibrate the infinity focus of this lens once you get it back after overhauling it.

IMG_2379The focusing ring should come off easily. If it is somehow stuck then it is due to the dried grease of some kind glue used on the factory. Do not force your way and apply some kind of solvent like alcohol on the screw holes and the seams of the focusing ring found under it and let it work for a bit before you attempt pulling this part away from the lens again.

If you look at the centre of the image around the lip of the helicoids, you will notice that I made several scratch marks there so that I will remember its configuration later during reassembly. These small marks will show me how it should be when the lens is collapsed all the way to infinity. These marks are important, so please do not forget taking notes!

IMG_2380Now it is time to remove the decorative sleeve with the focus scale and the grip. Remove the tall-headed screw encircled in the picture. This screw connects to the aperture ring so that the aperture fork assembly found inside also rotates with it.

IMG_2381Now that the tall-headed screw from the previous section is out of the way the shiny grip can now be pulled away but wait, there are screws securing it to the lens! Remove 3 of these and the sleeve and grip should come off.

IMG_2382Mine took some effort before it came off. Nikon usually glues this part to the main barrel or decades-old dried grease have caked these parts together. To free this up, use a couple of drops of alcohol and see if it works and if that did nothing to help then use benzine to help melt down the old grease or whatever is in it before you attempt to pull it off from the lens barrel. Just make sure to give it time to work before you attempt it.

IMG_2383The sheath is not only decorative and merely showing the scale but most importantly it is protecting the helicoid keys underneath it. Carefully use a screw that fits into the head of these screws and with a firm grip unscrew these off so that the helicoid key can be pulled off from the lens. The helicoid key keeps the helicoids in sync as you turn the central one, achieving focus as it collapses and expands. Note the orientation of the helicoid key.

IMG_2384Now that the helicoid key is gone, the helicoids can now be separated. I usually start with the outer helicoid and mark where it separates from the central helicoid. I scribed marks so I will know how they will mate when I need to reassemble it. Forgetting to do this will just result in a long and painful time trying to figure out where they should exactly mate.

IMG_2385You should remove this helicoid stop by unscrewing these 2 screws. This makes sure that your helicoids will not go past the focus range of the lens. This is in the way so this had to go and if yours will not budge then it must be glued stuck into the helicoid.

IMG_2386Again, always mark where the helicoids separate. This should be mandatory and I should not have to explain this every time I write something.

IMG_2388Back to the inner helicoid, you should remove this part also if you want to make sure this is a thorough job because gunk tends to accumulate under this part. This can be removed by saturating this part with alcohol and repeating the process until this ring is free. This part is usually glued to secure it and some even have 3 set screws just to make it stay put.

IMG_2387To remove the aperture fork and it’s ring, you must first saturate these parts with alcohol to soften the glue before you attempt to remove this part. The retention ring is glued into place just to make sure it doesn’t get loose over time. Once you are sure that the solvent has done the job of softening it, get a spanner and remove this ring but be careful not to scar the threads of the helicoid!

IMG_2390And off it goes! We have completely disassembled the lens barrel down to it’s basic parts!


This lens took me around 3 hours to overhaul because I needed to clean up the hardened gunk in between parts. It was pleasurable working with this lens and I enjoyed every bit of it, appreciating the high mechanical standards of years-gone-by.

Is this lens suitable for a beginner as his first lens? Probably, so long as you adhere to this guide and familiarise yourself first with the skills and tools needed for this craft. I would advise you to work on a cheap lens from another brand first if you are totally new to this thing so as to not waste any valuable Nikkors all for the sake of learning. This lens is very valuable and it deserves plenty of respect so treat it as a precision tool like a Rolex!

Thank you all for continuing to support! Are you liking this series on the 105/2.5 family of lenses or are you beginning to get bored? Please tell me so I will know. If you guys are still OK with this then I will continue next time with the lens that started it all. Thank you again for the support and see you guys again next time! Love, Ric.

Help Support this Blog:

Maintaining this blog requires money to operate. If you think that this site has helped you or you want to show your support by helping with the upkeep of this site, you can simple make a small donation to my account ( Money is not my prime motivation for this blog and I believe that I have enough to run this but you can help me make this site (and the companion facebook page) grow.

Helping support this site will ensure that this will be kept going as long as I have the time and energy for this. I would appreciate it if you just leave out your name or details like your country and other information so that the donations will totally be anonymous it is at all possible. This is a labor of love and I intend to keep it that way for as long as I can. Ric.


6 Comments (+add yours?)

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  6. Trackback: Repair: Nikkor 105mm f/2.5 Ai-S | Richard Haw's Nikon Maintenance Site

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