Repair: Nikkor 105mm f/2.5 Ai-S

Hello, everybody! I just had some old-style ramen with my family this afternoon. It’s not the same as what people are used to these days and its taste hark back to pre-war years. I enjoyed the simplicity of the taste and lightness of the soup. It showcased the bare-basics of ramen very well that you don’t need to add anything more to make it delicious. Today, I am going to show you a lens that’s not quite old but it has faded into obscurity for some of the younger photographers who prefer what’s “cutting-edge”. This lens will surely be a keeper if you know how to use it and I will teach you how in this article.


We are going to talk about the legendary Nikkor 105mm f/2.5 Ai-S and this is the final lens of the popular 105/2.5 family of lenses. This lens got its fame because this was supposedly used to capture the photo of The Afghan Girl. It’s the final and best version of a long line of lenses, I say it’s the best (optically) because it has the best coatings used and it has that very useful built-in lens shade. It is a very nice lens to hold because it feels dense despite it’s compact size, this thing is going to last you more than a lifetime if you take care of it.

IMG_2517The Nikkor 105mm f/2.5 AI-S lens gives you the impression of quality and reliability when you hold it in your hand. It inspires confidence with its very well-built barrel. It’s the real deal, a lens that was made for professionals to use in and out of the conflict zones.
IMG_2518Optically, the lens hasn’t changed from its predecessor but the latest versions of this lens made from the ’90s until its final run in 2005 has the best multi-coating applied to it. The optical formula haven’t changed but I suspect that Nikon tweaked the design slightly. This is just my suspicion so don’t take this as the truth. To be honest, a Nikon engineer told me personally that they don’t mess-around with the optical formula once it has been proven and the only thing they change is the shape of the walls to make the elements fit the wall of their new housing if ever the housing was also updated on a newer version of a lens. I am sure that there are exceptions to this.

IMG_7329.JPGThis is the only version of this lens with a built-in hood. It’s very handy but some people don’t like it a lot because it can easily be retracted when it gets knocked hard enough. It’s very convenient to shield that large front element from stray light hitting at an angle. I’m not sure why the other versions never had this convenient feature.

IMG_4256.JPGThese are all of the major versions of this lens family. It began in 1953 as the rangefinder version and the last one made its way out of the production line in 2005. This is almost 5 decades of continuous production! Nikon would never make another lens in this line due to the modern zoom lenses’ performance making this lens line obsolete and redundant.

The major versions of this lens family are (left to right):

There are numerous minor updates in-between these versions but they are too small to even mention. They’re insignificant to our article and will only confuse you that’s why I am only showing you the major updates to this lens. They are all optically very good and I love all of them so much that it literally takes me minutes to decide which one I should bring when I need a 105mm lens for portraiture. This is one of my secret weapons and I will show you why with my sample images below.

(Click to enlarge)

I don’t think that I need to take plenty of sample images for this lens because the optics is the same as the one in the New-Nikkor 105mm f/2.5 lens but for the sake of discussion, I’ll show you some pictures that I took with this lens. Just see how sharp it is wide-open and how smooth the transition is between what’s in-focus and what’s blurred. The relatively-low element count also gives this lens a very natural rendering of the scene.

(Click to enlarge)

There’s no better way to show you how good this lens is than to take some portraits with it. This lens was designed to excel in portraiture because Nikon found out that people are using the 105/2.5 lenses for portraiture and so they calculated it to render beautiful and natural-looking portraits, just look at how beautiful and natural her skin looks! If I’m not mistaken, I believe this shift happened with the decision to use the Gauss-type design for the New-Nikkor 105mm f/2.5 since this is the only big change this lens family ever had in its almost 50 years of production. This was documented in one of Nikon’s online articles so if you’re interested in this subject just search for it online.

That’s all for the introduction. If you want a more complete history of this lens, please go and read about the other versions of this lens that I have featured in this blog. This is one of Nikon’s most interesting lens category and is one of the lenses that gave the Nikkors a very-respected name in optics. This lens family took some of the most important photos in the past couple of decades, from Vietnam to more recent conflicts. In fact, I read about a photographer who still uses this lens to take photos in conflict zones. This is one of the best deals in portrait lenses so if you ever saw one, grab it before somebody else does!

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 now-growing 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.

Disassembly (Main Barrel):

The main barrel is of conventional design and it isn’t difficult to take apart for somebody who have been working on Nikkors for some time. It shares plenty of similarities with its smaller brother the Nikkor 85mm f/2 Ai-S lens and if you have experienced working with that lens then this lens should be very familiar to you. The glass is big and heavy on this lens so be careful when you’re working on this lens.

IMG_0157Begin by removing these screws.

IMG_0158And here’s another one.

IMG_0159You can now safely unscrew the front barrel from the rest of the lens. The bigger screw is used for securing the front barrel and the 2 smaller ones are for the name ring.

IMG_0160The front barrel secures the objective so you can safely extract it now that it’s gone. Store the objective in a safe place to prevent damaging it while you work on the main barrel. It is dense and heavy so make sure that you don’t drop this to the floor!

IMG_0161Now that the objective is gone, you can now safely work on the rest of the lens. There are 3 screws that secure the bayonet mount and you should remove them carefully. Read my guide on removing screws to prevent damaging yours. Make sure that you use the right screwdriver type because these are not Philips screws.

IMG_0162The bayonet mount should come off easily now that the screws are gone.

IMG_0163Wow, just look at that! Just like what the sailors say – “She may look clean…”; I’m glad that I took this lens apart because this is unacceptable. If I left the lens like this for a couple of months more then it may have been a disaster! Remember to never put too much grease on the helicoids because this lens can be prone to the oily iris problem.

IMG_0164The aperture ring can’t be removed just yet. You will have to unscrew these first because they connect the aperture ring to its fork on the other side.

IMG_0165Once the screws are gone, you can now safely remove the aperture ring.

IMG_0166This is the aperture fork. It couple the aperture ring to the iris mechanism inside the lens so the iris can open and close as you turn the aperture ring. See how greasy it was? Don’t apply any grease on this thing because any oil on this part may migrate to the iris and it’s going to be a bigger job when that happens because you will have to open-up the iris just to clean it properly and overhaul this lens again just to make sure that it’s clean again.

IMG_0167The rubber grip has to be removed so you can take apart the focusing ring. Use a wooden toothpick (round type) and run it underneath the whole circumference of the grip so that it will lift the rubber from the glue that was used on this. Be careful not to tear it.

IMG_0168The distance scale is merely taped to the focusing ring. It’s flimsy but it works. Most Ai-S lenses got the same thing going on. It’s a cost-cutting decision and there are times when it would undo itself and cause the scale to be off by a bit. You can remove the tape now or you can opt to remove it later,

IMG_0169Get a proper-fitting screwdriver and remove these small screws. There are 3 of these and they secure the shiny metal grip to the main barrel.

IMG_0170Before you can remove the grip, you will have to remove this clicker spring because it is in the way. Don’t forget to put this back later.

IMG_0171The grip can now be safely extracted.

IMG_0172The focusing scale can now be removed. Notice that oil has settled underneath it.

IMG_0173There are 2 helicoid keys on this lens and this is just one of them. The helicoid key is used for syncing the movements of the helicoids so you can achieve focus. Since there are 2 of them, mark one of them so you will know which key should go to which side.

IMG_0174Now that the helicoid keys are gone, you can now turn the helicoids independent of their rotation range. This is how far the central helicoid will collapse and I made a mark just to remind me how far it goes. During reassembly, if I got the same configuration as the one in the picture then I have succeeded in putting the helicoids together properly.

IMG_0175Time to separate the helicoids. This is where they separated and this is also how they will have to be meshed together. If you are new to this, read my article on how to work with helicoids. This is very important because this is where many people get stuck. That’s why you will see some lenses that were badly put-together and then sold for junk online.

IMG_0176The inner helicoid can now be extracted. Again, never forget to mark where the helicoids separated. It’s such a simple routine but many beginners forget to do this despite all the warnings I gave.

That’s it for the lens barrel. Make sure to clean the helicoids properly before you grease it so the fresh grease will never be contaminated with the old grease. It looks like the lens was lubricated with a type of cheap lithium grease. I use good quality silicone grease for my lenses, never go the cheap route when dealing with lubricants.

Disassembly (Objective):

Disassembling the objective is pretty straight-forward. It’s of the conventional rack-focus type so there are no tricks involved in this lens like CRC. The inner elements of this lens are prone to accumulating dust from the iris or elsewhere. Air gets sucked into the inner chamber where the iris mechanism resides each time you focus the lens and the dust can come from a variety of places such as the gaps between the barrels, aperture ring and its bayonet mount. There’s not a lot of ways to prevent this, it’s just part of using this lens.

IMG_0177The front elements cell can be easily unscrewed with your barehands.

IMG_0178The rear elements cell can be easily removed with your barehands. Dirt usually settle in the inner walls of this part and you should blow it away using a bulb blower.

I mentioned before that this lens can be prone to the oily iris problem because it is very compact so the helicoids are closer to the iris mechanism. Any excess oil coming from the helicoids will travel to the iris mechanism via the aperture coupling fork. Fortunately for me but unfortunate for you, the iris on my lens is clean despite the disgusting oily mess that it had. If you need to clean the iris mechanism then just check out my article for the Nikkor 85mm f/2 Ai-S or other similar lenses like the New-Nikkor 105mm f/2.5 lens. Their construction is similar so there aren’t any surprises here.


That’s all for the Nikkor 105mm f/2.5 Ai-S and all you need to do now is to adjust this lens’ infinity focus. Reassemble the lens but don’t reinstall the rubber grip and do not tape the distance scale. Calibrate the infinity focusing properly and then tape the distance scale to the focusing ring once your lens can properly focus to infinity. Make sure that the symbol for infinity is dead-center to the big black dot on the focusing scale before you tape it. It’s now OK to put-back the rubber grip. You may want to apply a bit of contact cement just to make sure that it sticks. Remember, you only need to apply just a little bit or else it will create a mess. If you are new to repairing lenses, read my old article on how to calibrate your lens’ infinity focusing. It’s essential that you do this properly or your lens will never focus properly and the distances on the scale will never match.

IMG_0179This lens deserves to be taken-cared of. It’s one of Nikon’s best lenses of all time for me so I’m heavily biased towards this lens. It’s great knowing that the grease in there will last a long time before breaking-down again. You only have to do it once if you did it properly.

We have finally finished this series on one of Nikon’s most iconic family of lenses. For the people who know about this lens, this is just reaffirming what they all knew and why the lens is a keeper. For those who are new to this lens, I hope that this article will give you a better appreciation of what went before and also an appreciation of the finer things that a lens can do. It’s not always sharpness, bokeh and other measurable things that count. It is often the intangible things that makes a lens so special.

Thank you for following me on this blog. I hope that this article will be useful for you so you can fix your own lens. If you are new to this, just give the lens to a repairman. This is not a DIY project for a beginner. You may end up wasting more money if you ruined your lens as opposed to spending money for a proper repair. Remember, my blog is only here to entertain and educate you. If you really want to get into repairing lenses then start on a cheap Canon lens or anything that you can destroy without any guilt. This lens deserves to be respected and should never be ruined by a beginner. See you guy next time and if you liked my work, please share my blog to your camera group! Thanks again, Ric.

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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.

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Thank you very much for your continued support!


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.


1 Comment (+add yours?)

  1. Trackback: Repair: Auto-Nikkor-P 105mm f/2.5 | Richard Haw's Nikon Maintenance Site

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