Repair: Micro-Nikkor 105mm f/2.8 Ai-S

Hello, everybody! I am feeling very well now, thank you very much for the well-wishes and messages that I received! The weather is beginning to get warmer as Spring is just around the corner now. Spring brings plenty of seasonal things like migrating birds, hay fever, the numerous seasonal produce that I enjoy and most especially – bugs! Bugs are shy creatures and taking pictures of them can be a challenge at times. For that, you will need a lens that will give you enough subject to lens distance. For me, that is only the job of a 105mm lens!


Today, I am going to introduce you to the Micro-Nikkor 105mm f/2.8 Ai-S lens! This is a very versatile lens for portraiture, macro and just about everything. It’s an advanced lens that was way ahead of it’s time when it was introduced and it’s still available now NEW for use with the scientific community where in precise manual focusing in high magnification is important. How many lenses can boast of such longevity? Not a lot!

img_1986The Micro-Nikkor 105mm f/2.8 Ai-S lens is still being produced now in 2017. That is around 34 years of continuos production since it’s debut in Spring of 1983! Can you imagine that!?

The 105mm line of Micro-Nikkors have a very long tradition starting with the bellows lens from 1968 to the AF-S VR Micro-Nikkor 105mm f/2.8G IF-ED lens of today. This line of lenses has always been popular with bug shooter because 105mm gives you just the right distance from your subject so you won’t scare it away or get in the way of your own lighting. It also gives you just the right compression so your subjects aren’t distorted by foreshortening. If you want something that is wider for things like food or product photography wherein the perspective is important so your subject don’t look flat or small then you’ll definitely want the Micro-Nikkor 55mm f/2.8 Ai-S lens or the Micro-Nikkor -P 55mm f/3.5 lens. If you want a lens that has history the the Micro-Nikkor 5.5cm f/3.5 preset lens might excite you.

This lens is a huge leap technologically since it incorporates Nikon’s CRC floating elements technology wherein the objective changes geometry as you focus in and out and the scale in the focusing ring shows you the optimal aperture settings for best sharpness or depth of field at any given distance when used with the PN-11 that this lens is supposed to be used with in order to achieve 1:1 magnification. Like most Micro-Nikkors before the AF era, this one is only capable of reaching 0.5:1 on it’s own and it needs an extension ring to get to 1:1. This design compromise has a lot to do with handling and engineering limits of it’s time, now we take 1:1 magnification for granted! Going back to the scale, it also shows you the correct magnification when you have the PN-11 extension tube or not.

junkHere it is with one of it’s predecessors, the Micro-Nikkor 105mm f/4 Ai lens. The older lens is basically a high-performance bellows lens that was fitted into a focusing unit. It is very popular and well-regarded amongst macro shooters because of it’s magnification and the insane image quality. The problem is the f/4 maximum aperture really isn’t very useful if you are on higher magnification as it can get really dark as you get closer. Add the PK-11 or similar extension tubes and the view gets even darker, making accurate focusing a pain.

The Micro-Nikkor 105mm f/2.8 Ai-S lens’s direct predecessor is the Micro-Nikkor 105mm f/4 Ai-S lens, it is an improved version of the the lens that you see in the picture above and it also has that chrome knob for damping focus. Some people use this as a focus lock of some sort but I think that it is too weak for that especially if you have things attached to the lens like your lighting setup,etc. It may be sufficient but if your setup is heavy enough then it’s gonna affect it over time when you have the lens pointing up or down. When the padding underneath that is worn then it gets even worse. I will show you the mechanism for that in the disassembly section.

Here it is with the various lighting options that I use for shooting macro. If I want to have a more directional look, I will use my inflatable soft box but my favourite so far is the ring light setup. The Sunpak 16R Pro ring light kit is a powerful and small setup that is perfect for macro and portraiture. The tube is a contiguous toroid so there are no dark spots in the illumination unlike some other designs so the catch lights in the eyes remain circular but some people will prefer separate tubes so they can control lighting ratios. I can achieve it by wrapping waxed paper or colored plastic bags on parts of the light. Cool,huh?

Optically, it is made up of 10 elements in 9 groups which is more complicated than usual as far Macro lenses of it’s kind goes. This is because it needs to accommodate the CRC unit so the lens can deliver sharp images regardless wether you are focusing near or far. Without the use of CRC, some traditional lens designs will give you sharp images at one end of the focusing spectrum and so-so sharpness at the other end. CRC is a clever solution to fix the issue by moving one or more element groups as a unit as you focus in and out. The change in geometry compensates for the lens design’s weakness at one end of spectrum. This will make the lens more complicated to work with as you will soon see.

(Click the images to enlarge)

Here are some samples shot with this lens. The bug shots were shot last year before Fall so don’t get any ideas that we have this much bugs this early in the year. The rest were shot this morning. Wide-open, the f/2.8 maximum aperture clearly shows that this lens is good for blurring the background out. Even at f/16, you can see that my bug pictures still have a bit of separation between the subject and the background. This is one of the reasons why a 105mm lens is great for bug photography. The turtle, football and duck pics were cropped. I would like you to pay attention on the turtle picture, notice the magenta color shift? This can be a problem when you have a high-contrast object that is not in focus in your picture. This isn’t really a problem because this phenomenon only shows up in special cases. I shot the bug pictures with my Sunpak 16R Pro by the way, notice the nice light-wrap effect.

This particular lens was bought from the junk shop and you can see from the pictures how bad this thing was. The clear lacquer coat is worn and the only way to restore this back to it’s former shiny state is to strip this to metal and repainting this. I do not have the time for that so I will just leave it as-is. I was very pleased of the results of the lens so I restored this so the operation is smooth.

OK, enough of the history and babble and let the dismantling begin!

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.

Disassembly (External):

Since this lens is not made in the traditional focusing unit/objective configuration and due to the more complicated construction due to the implementation of CRC, I will be going from one end of the lens to the other very often in this blog post. To make it less confusing, I’ll be going through it in stages so don’t worry. This is certainly not a lens for beginners as it is way too much for them to handle due to the numerous interlocking parts inside. Do not try to overhaul this if you are new to this. If all you want is to clean a lens element or two then this might be OK as most of the lens elements are easily accessible but you will need special tools for this task. Lubrication and overhaul? Leave it to the experts this time.

We will begin with the external part since this is the easiest part to access and the natural step for anybody working with this lens. I got a bit confused and I didn’t follow the steps progression perfectly but I will do my best to present it to you in a logical manner so that you will not waste your time.

img_1988Remove these screws on the bayonet mount. If they won’t move then you will have to put a drop of acetone or MEK on each of the screws and let that dissolve whatever was used on them before you attempt doing it again. It can take 30min to a couple of hours so please be patient with this step. If you want to be quick about it then you will want a butane torch. I also want to stress that you should use a JIS screwdriver for this and get the one with the longest shaft since a long-shafted driver will give you more torque. Finally, use the weight from your shoulders to prevent slippage. This is an acquired skill.

img_1989The rear bayonet comes off just like that as there is nothing connected to it that will snag.

img_1990Before you get excited and start removing the aperture ring, make sure you remove these 2 screws first because the aperture ring is connected to a mechanism inside. Forcing it will result in damaging this part.

img_1991Once the screws are gone you can now safely remove the aperture ring. See all that dirt?

img_1993Now, here is a good view of how it should look like from the factory. I took this picture as a reference so I won’t get lost later during reassembly.

img_1987Now, let’s go to the front. Carefully remove the rubber sleeve and make sure you don’t rip it because just like grandma’s bones, they can become brittle with age. These are usually glued so run a toothpick underneath the rubber sleeve to unstick it first then carefully tug it until it comes off.

Go back to this step when you are almost done reassembling your lens and it’s time to do the infinity focusing calibration part.

img_1992You can remove this set screw for now so you will not have to deal with it later. It secures the front ring so it won’t get unscrewed accidentally. We will deal with this part again later so for now, place a couple of drops of acetone to soften the glue used on it’s threads. Drop it along the seams and let capillary action take the acetone into the rest of the thread.

img_1994You can now begin removing these brass shields. The scotch tape is used to hold both the brass shields and the focus scale in place. The brass shield protects the nuts underneath it.

img_1995Carefully mark the position of one of these screws. It is responsible for keeping the front barrel in sync with the CRC unit inside. You can remove these screws later.

img_1997Remove the 3 screws securing the chrome grip so you can take it off. Once that is gone, the focus scale and other things can safely be removed.

img_1998This sleeve can be removed as well. Just look at all that dirt that got accumulated in here!

img_1999This is the focus damp mechanism after dismantling it. It is being held by a C-clamp. This is part of the focus scale and you can skip this if you want to but for a thorough cleaning, it has to be dismantled. you can replace the worn felt pads on the spring if yours doesn’t grip the lens properly anymore but make sure that the adhesive you use is strong enough.

img_2001This is a good time to take notes, both visual and physical. This is the proper alignment of the front CRC floating elements on my lens, it may be different on yours.

Disassembly (Internal):

That was easy isn’t it? Things are going to get more difficult from this point so pay special attention to everything you do and take notes and pictures before you dismantle anything. Also be very strict with yourself when it comes to maintaining the focus of your lens and making sure that it is always set to infinity especially when taking notes. This will be your point of reference and if you got it wrong (like I did) then you are in for a helluva time.

img_1993Now it’s time to separate the helicoids! Remove the 3 screws to the left and the 2 screw on the right. Before you separate the helicoids, that brass thing is getting in the way so let us look at the ext step first.

img_2002Now, time to disassemble the lens further. Remove the 2 screws that’s securing the brass part. This was connected to the aperture ring before we got rid of it. Be sure to make some marks so you know that these are aligned properly when you reassemble the lens.

img_2003Carefully get that thing out of the way…

img_2004Now that nothing is in the way, we can now separate the outer helicoid. As far as helicoids go, you must never forget to mark where they separated because this is also the position that they are going to mate later on. Check the picture above and you can see that I made a mark to indicate where they separated.

img_2005Now, time to get that delicate rear elements group out of the way. Use a lens spanner for this and stick it in the slot found on the casing. You can do this earlier if you want to but it just occurred to me now so don’t worry.

img_2006Pick the rear elements group with your fingers and keep it somewhere safe.

img_2007This is the other half of the lens. At this point, you can pull those long helicoid keys from the rest of the lens. These were connected to the base of the outer helicoid and it keeps it in sync when you focus in and out.

img_2008Just to be safe, I marked where the midline should be. Better safe than sorry!

img_2009Now, the central helicoid can be separated from the rest of the lens. Again, never forget to mark where they separated. If you look at my picture, you can see where I marked mine.

img_2010You can remove the focusing ring but be careful with it because it will snag with that small tab from the CRC mechanism. A little bit of dexterity will be needed here.

img_2012From here on we are just going some parts here and there in no particular order because it is all clear for us to do so until we reach the delicate CRC assembly itself.

In order to access deeper into the inner barrel’s parts you must first remove this ring. It is being held held in place by 3 screws so you will have to remove those first.

img_2013Next, remove this cup. This cup rotates and is in charge of actuating something. If I recall it properly, it actuates the iris each time the stop-down lever operates.

img_2014Time to remove the inner helicoid from the objective’s casing. Unscrew these and look for the other ones on the other side that is hidden from view.

img_2015And the objective can now be separated from the inner helicoid. Do not forget to mark their position in relation to each other by the way.

As you can see from this picture, the lens has a tendency to develop the oily iris syndrome. Any lens which has the iris mechanism close to a helicoid is at high risk so please apply it sparingly since a little grease can go a long way but not too thin since it will dry up rapidly.

Disassembly (Objective):

Disassembling the objective isn’t really difficult if you know what you are doing. The only thing that I remembered was how it was a pain to remove some of the retention rings due to these being glued or sealed by black paint. This issue is most especially true of the front elements assembly. Just use a lot of patience and care so things will go your way.

img_2016Unscrew the rear baffles with your bare hands. Be careful because the rear element might drop to the floor since this is the one keeping it down. Remove the rear element with lens sucker and keep it safe. Do not forget to mark which side should face where with a pencil or a sharpie! This will help a lot when it’s time to reassemble this. I usually mark the wall of the lens with a thin line facing the front of the lens.

img_2017Next, carefully remove this spacer and do not forget to mark which way should be facing forward. These spacers aren’t usually symmetrical and you will risk damaging your lens if you put it back facing the wrong direction.

img_2018Next, use a lens sucker and pull this thing out of the way. For very obvious pieces like this, I wouldn’t bother marking which side should be facing where.

img_2011Now, back to the front! Do you remember the front ring that we applied acetone to after removing the set screw? Now it’s easier to remove since we gave the solvent some time to work on the glue. Nikon loves to use glue on the front rings of their lenses.

img_2019With the ring gone, you can now unscrew the front elements group away from the objective so you can keep it in a safe place. You can do this step earlier if you wish but I had to wait for the solvent to work on the glue first so I worked on the other parts of the lens first.

img_2062In order to open up the front elements group, you will need to unscrew this retention ring first. As you can see, it is glued again with lacquer. Alcohol will do a quick job on this.

img_2063After a few drop of alcohol, the ring came off without any effort. Just remember to use the correct spanner for this and be careful NOT to scratch the glass!

img_2064You can now proceed by extracting the glass with a lens sucker or your fingers.

img_2065Now, on to the front!  This ring has to be removed but it was secured with paint. Before you begin working on it with a compass, use a needle and dig into the seam where this ring and the casing meets. This is to remove the paint sealing the seam so you can drop alcohol into the seam itself. This part can be hard to remove by the way so be patient.

img_2066OK, after a couple of minutes I tried attempting it again and the ring came off easily due to the solvent seeping into the thread and working on the adhesive and paint. See that thing sticking out from the edges of the ring? That’s the dried paint that’s sealing this cell.

img_2067Next, use a lens sucker to extract the front element. Remember to do this with the front elements group facing up or you will drop everything to the floor! I warned you.

img_2068What’s this? more rings?! Use a compass and be careful not to scratch the glass element.

img_2070As evident from the picture, this ring was also sealed with black paint like the one before.

img_2071Now that the ring is gone, you can use your lens sucker to pull that 2nd element out of the way. I usually store these in a small plastic box with plenty of lens tissue as cushion.

Disassembly (CRC):

This part is really critical. You will have to make plenty of notes and take plenty of pictures before you dismantle anything. You will have to be very careful of the tolerances and count how many how many turns you need to remove something. It is also very helpful to study how a mechanism works before you dismantle it so you will know if you got it right when you reassemble it later.

img_2020Before going any further, make sure to take plenty of pictures of the iris and the 2 helicoid keys for the CRC. Note their positions,etc. That brass ring you see in the middle of the pic is a spacer for the front elements group. Remove it and keep it in a safe place.

img_2021Again, take more notes and pictures while you still can. This time, on the outside. This is a very important part so get the tolerances and measurements right!

img_2022Once you are satisfied with your note-taking, you can remove the 2 helicoid keys found in the front barrel.

img_2023You can now remove the front barrel…

img_2024And safely separate the front CRC helicoids. Again, be sure to mark where they separate!

Disassembly (Iris Mechanism):

The iris mechanism is pretty straight-forward, the only thing noteworthy is the protective plate used to cover the inner parts of this assembly. It is glued so you will need to use a lot of solvents to get that off. You will have to be careful while picking this thing and be sure that the iris is fully open when doing this so you will not accidentally snag anything. The blades are very delicate so handle these with care.

img_2026Now, remove this protective plate from the iris mechanism. It was glued on mine so I had to soak the edges with alcohol first before attempting to remove this thing. Be careful not to damage the blades when you remove this plate! Do it while the iris is wide-open.

img_2028See the iris’ shape? It’s irregular. While odd-numbered irises have a tendency to do this, this one is on the bad side. It’s caused by improper seating of the blades, a warped blade or all of the above. I fix this problem by reassembling the iris blades and hoping that the iris blades will even up now that they are randomized a bit. This trick usually works and in bad cases, the iris will still be a bit irregular but not as bad as before. An irregular iris will give you ugly egg-shaped bokeh and nobody wants that.

Before you go any further, use a sharp pair of tweezers and remove the spring. Make sure not to damage the spring or the blades!

img_2025Now, to open up the iris you will have to remove these set screws. I believe there are 3 of these overall and the others are on the other side. These screws secure iris mechanism.

img_2029The iris mechanism can now be removed as a single unit.

img_2030The blades will be cleaned thoroughly with lighter fluid and a clean lens tissue before we put them back.


Wow, that was one complicated prime lens! It’s a pretty good exercise and I sure learned a lot from this. I got confused because I made bad notes while I was dismantling the front of the lens where the CRC unit is located. When it comes to lubricating the helicoids, be sure not to lubricate them too much or you might end up with an oily iris when the excess oil migrates to the iris. The helicoid for the CRC unit doesn’t need a lot of grease anyway so it is OK to just leave a thin film of grease on it for lubrication. Also be sure not to use a heavy type of grease or else you will end up with a lens that is hard to focus. I always use a lighter type of grease for lenses with CRC like the Micro-Nikkor 55mm f/2.8 Ai-S lens. Lenses that have CRC have more helicoids than usual lenses that don’t and all the resistance coming from all those damped helicoids will all add up so will you need to take that into account.

The Iris mechanism can be tricky to put back but there is a trick that I do and I will show it to you later. First, check out the newly rebuilt iris!

img_2031See? now it’s not shaped like a lemon anymore! Well, it’s still a little bit irregular because of the odd-numbered blades but at least it looks a lot better now.

img_2032To easily restore the iris mechanism back into position, you need to place it on top of a cup or something that is a bit smaller than it’s diameter and then carefully lower the case so it is not disturbed or else everything will fall apart. Secure it with the set screws again and it is as good as new! Finally, return the spring to it’s proper place after all this is done.

img_2033Reassemble your lens up to this point and check to see if it’s focusing correctly all the way to infinity. Focus on something 4-6km away or more and using the focus confirmation dot on your modern Nikon camera to make sure that it is focusing correctly. Check the image that you took on your camera’s LCD to make sure that it is sharp. Now, the dot may light up but the focus is not spot-on so take a series of pictures to see which one gives you the sharpest result at infinity and then adjust the focus scale to reflect that. This can be a bit tricky and tedious but you have to get this to focus perfectly at infinity or else the other distances will all be incorrect according to the scale.

That’s it for this post! I want to show you something different this time so I thought that a more complicated prime lens would be good so I hope you enjoyed this. Now, I am not sure wether people actually read these things from start to end but I hope that you do because I put a lot of care and effort into writing and editing the sequence of the steps!

I will be covering CP+ for everybody next week and I will take a leave from the studio just for that so tell me what you want to see from this year’s CP+ and I will make sure to cover that for you,too! See you again next week and please share this blog with your friends or photography club! I sure need all the exposure I can get! 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.


5 Comments (+add yours?)

  1. Trackback: Internet Nikon Repair Resources – My Take on Photography and Diving (Underwater Photography Mostly)
  2. John A. Koerner II
    Feb 23, 2017 @ 03:04:10

    Nice work and great detail.


  3. John Koerner
    Feb 23, 2017 @ 03:05:13

    Nice work and great detail.


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