How (NOT) to take apart a 50mm f1.8 AI lens.

[Incongruent Phonon]

Good afternoon. I just took apart my nikkor 50mm f1.8 manual lens. I really enjoyed the experience and have a few things that I would like to share with you. Especially other aspiring amateurs who are trying to get into lens/camera repair.

 

. 

[Incongruent Phonon]

The reason i took it apart is there are dust under the rear element, and the barrel of the lens seem loose.

got the lens from online site. Could have chose to return. Didnt want to abuse the policy because im 80% sure im just being picky about an otherwise mint good condition lens. 
 

so how about i take it apart, without even the proper tools, as a complete noob to photo gear servicing and void the return policy completely, risking damage and further cost?

 

sounds like a good plan. I vouch for it. 

Armed with a disassembly video, a rubber band and a micro Phillips screw driver, I went to town on this thing. 

first step is the outer ring. Man in the video used a very professional looking rubber ball. I put the rubber band around and it came off nice and easy. 

 

 

[Incongruent Phonon]

Under the cap with the specs and ‘nikkor’, there is a ring holding the front element down. Three screws and it comes off. No headache.

The front element also comes off with three screws. There are some markings around the front element, presumably indicating which way it shall be put back in. I….. i didnt pay attention to them at all.

[Incongruent Phonon]

Under the front element is the aperture blades and the focus ‘helicoid’. 
 

The original plan is to stop right here because i have done limited research before I took the lens apart, and was aware that it is a very delicate piece that needs to be aligned precisely foe the focus to work. At this point i already had access to the other end of the rear element and already have blew the dust off. 
 

But i got too confident! Until now it was all very easy, a total of six screws got me to this point and i figured: what could be so hard. 

[Incongruent Phonon]

Following the tutorial, I removed the focus ring which is also held by three screws, onto the brass ring responsible for advancing/retracting the helicoid. As soon as I pulled the thing off thinking huh this is easy, the man in the screen said: you need to mark the position of the focus ring. 
 

here comes my downfall. I obviously did not mark the position of the threads, and i was not even sure if I turned the thing all the way to one end. So in a panic I started turning the brass ring, hoping it will reach a stop so I could figure out how the focus ring aligns. 
 

jokes on me. If I had turned it towards the infinity end, it would retract and reach the infinity end and stop. 
 

BUT I DIDNT. I TURNED IT TOWARDS THE CLOSE END AND THE F******* ENTIRE HELICOID ASSEMBLY POPPED OUT. 

 

So i was sitting here, looking at all these peculiar components, pondering how on Gods green earth should I put it back. 

Edited April 4, 2023 by Incongruent Phonon

[Incongruent Phonon]

Now I have two problems. 
 

problem A: I have no idea where the threads should start or end. 
 

problem B: I can not even take the lens mount apart and try to at least ‘correctly’ assemble it. The three screws on the mount end absolutely will not budge, and I dont wanna force them and risk stripping them, So i budged and I left the lens mount alone. 
 

At this point, i could either admit the defeat and send the lens to a repairer, pay about the cost of the lens and hope I will see it again in my lifetime. 
 

Or I could try to put it back together the way it came out.

 

upon close inspection, there are two tabs where the helicoid engages the base of the lens. One tab that goes up through a little window on the helicoid assembly, and a clamp that accepts a tab that comes down from the helicoid assembly. 
 

they are marked on the picture with red circles. 

[Incongruent Phonon]

Picture showing the little window where the tab from the base mount is supposed to poke through. 
 

The good news is since there are two tabs(that i am supposed to take off before i even screw out the helicoid) to help me locate the position of the threads, the combinations between the thread timing of the helicoid assembly, the brass ring and base mount becomes finite. With a rough idea of where the rear element of the lens should be at furthest focus, there is a small chance that I could get lucky and find that right combo, thus get an useable lens out of this mess.
 

The bad news is the entire ordeal turned out to be extremely difficult.  

[Incongruent Phonon]

On this picture, you can see a groove that interrupts the threads of the helicoid assembly. There are two of them on each side of the assembly. They are supposed to engage two metal rails on the lens mount. 
 

The relationship is as follows: 

-Helicoid assembly meshes vertically with two fixed guide rails and two moveable tabs on the base mount. 
-Helicoid assembly also threads into the brass ring that advances it. 
-The brass ring threads into the base mount. 
 

You could probably already see the pickle I got myself into. Once the helicoid assembly meshes with the rails it wont be able to turn at all, only travel vertically as you turn the brass ring, Before it engages the rails the position of the two tabs also need to be perfect. On top of that, the timing of threads on the brass ring, base mount and helicoid assembly has to be just right for me to be able to send the assembly vertically back where it came from, properly engaging all the tabs,  

[conrad_hoffman]

I can't tell from the photos, but the vertical anti-rotation rails are usually removable, though the screws will probably have Loctite or something. Do you know about JIS and JCIS screwdrivers? Without them it's easy to destroy the screws. Usually Wiha drivers will fit well enough if you keep enough pressure on them. Possible Wera and Vessel too. Apply a very hot soldering iron to the screw heads to heat them up and maybe soften the Loctite (or whatever the Japanese equivalent is). In general, Nikkor AiS lenses are assembled as a complete module that then goes into the helical focuser. If you assemble the lens portion you can probably measure where it focuses so you know how the focuser needs to go together. Nothing specific to your lens, but a good site for repair info is http://rick_oleson.tripod.com/ Again, nothing specific to this lens, but my page on the 55mm Micro Nikkor might have a hint- http://www.conradhoffman.com/MicroNikkor55.html

FWIW, a few good sized specs of dust don't bother anything and the risks don't outweigh the rewards of disassembly to remove them.

 

[Incongruent Phonon]

This have becomes a rubiks cube! Turn the brass ring, position of the helicoid changes. Turn the helicoid, position of the brass ring changes. There is little space between the helicoid assembly and the base mount. More over, the ‘receptacle’ and the upward tab on the base mount are positioned in an angle that there needs to be spring tension between the downward tab and the window on the aperture blades for the helicoid assembly to properly engage. 
 

A rubiks cube. A rubiks cube up in my face, laughing in Japanese. 
 

Fortunately i was able to use a little trick to unjam myself. The part that keeps hanging up is the downward tab from the helicoid assembly. It travels with the aperture blades one way but not the other. The aperture setting ring needs both tabs combined to function properly. I simply have no way of controlling where that piece ends up as I retract the helicoid into the lens mount. 
 

fortunately! I realized that I could turn the aperture ring to march the position of the receptacle, located on the aperture ring, instead of just hoping that the free floating downward tab would magically mesh. 
 

So I thread the helicoid assembly onto the brass ring threaded onto the base mount, turn it so it engages the guide rails, make sure the upward tab from the lens mount goes through the little window, and I turned the aperture ring just a little to match up the position of the downward tab. 
 

wallah! It went back in! 
 

Took me three tries to finally have the focus ring line up with infinity as the rear element reaches the end. But at last. It worked. I think. 
 

 

[Incongruent Phonon]

Replacing the rest of the pieces was a breeze. Although I probably didnt put the front element back the way it originally was. There are nothing mechanical there so I think i should be fine. Right?…. Right??

 

I kinda want to run the lens just like this, without the cover. Anyone care to tell me if its a bad idea? Other than dust getting in?

[Incongruent Phonon]

3 minutes ago, conrad_hoffman said:

I can't tell from the photos, but the vertical anti-rotation rails are usually removable, though the screws will probably have Loctite or something. Do you know about JIS and JCIS screwdrivers? Without them it's easy to destroy the screws. Usually Wiha drivers will fit well enough if you keep enough pressure on them. Possible Wera and Vessel too. Apply a very hot soldering iron to the screw heads to heat them up and maybe soften the Loctite (or whatever the Japanese equivalent is). In general, Nikkor AiS lenses are assembled as a complete module that then goes into the helical focuser. If you assemble the lens portion you can probably measure where it focuses so you know how the focuser needs to go together. Nothing specific to your lens, but a good site for repair info is http://rick_oleson.tripod.com/ Again, nothing specific to this lens, but my page on the 55mm Micro Nikkor might have a hint- http://www.conradhoffman.com/MicroNikkor55.html

FWIW, a few good sized specs of dust don't bother anything and the risks don't outweigh the rewards of disassembly to remove them.

 

I am aware od the JIS drivers. I am also too cheap to invest in a proper set 😞 having done this, im seriously thinking about it. 
 

i stopped at the three screws on the rear mount because they wont budge. I did not want to force it. Thats why I had to go through  all the trouble and put it back the way it came out, Lucky for me, that actually helped narrow down the range of possible positions. 

Thanks foe reading and responding! 

 

[Incongruent Phonon]

Popped the lens on a FM body and tested the functions. Seems like everything works and focuses correctly. 
 

for the most part. It gets a bit stiff at the very end towards the infinity marker. It seems to pinch the aperture ring as the latter becomes harder to turn when the focus ring is fully to the end. Which is just the minor timing between the threads. I am not fussing about it. 
 

Aperture blades move smoothly regardless of position of focus ring. Believe im in the clear here. 

[conrad_hoffman]

It sounds like you're on the road to success! As for the element, they're centered extremely well when the OD is ground. I don't think Nikon worried about rotational position on lenses like that. Maybe a $12k pro lens, but not a nifty 50. Nikon made a lot of different 50s over the decades. Some good, some not so much. IMO, that one is quite good.

[Incongruent Phonon]

43 minutes ago, conrad_hoffman said:

It sounds like you're on the road to success! As for the element, they're centered extremely well when the OD is ground. I don't think Nikon worried about rotational position on lenses like that. Maybe a $12k pro lens, but not a nifty 50. Nikon made a lot of different 50s over the decades. Some good, some not so much. IMO, that one is quite good.

Thank you for your kind words : D i did see a yellow line painted on the other side of the front element. Figured it must have been trying to tell me something. But i am way too obtuse for the vintage orient riddles! 

[JDMvW]

Hope it works out for you.

My personal saga relates to the cheap Meyer Domiplan 50/2,8 used as the default 'factory' lens for many of the VEB Pentacon basic cameras.

Failure of the automatic aperture is legion! Not so much in the Exakta mount version though.

 

Marking with a pencil where threads, etc. come together is highly advised BEFORE dis-assembly.

 

Be prepared for the 42mm mount version to stop working if it hasn't already done so.

Edited April 4, 2023 by JDMvW

[Incongruent Phonon]

1 hour ago, JDMvW said:

Hope it works out for you.

My personal saga relates to the cheap Meyer Domiplan 50/2,8 used as the default 'factory' lens for many of the VEB Pentacon basic cameras.

Failure of the automatic aperture is legion! Not so much in the Exakta mount version though.

 

Marking with a pencil where threads, etc. come together is highly advised BEFORE dis-assembly.

 

Be prepared for the 42mm mount version to stop working if it hasn't already done so.

They are honestly not super complicated, from a mechanical standpoint. It’d be great if the manufacturer could simply mark it when the lens was made, would make servicing so much easier.

[roland_vink]

Take a look at these articles on lens repair:

https://richardhaw.com/2016/02/15/repair-nikkor-50mm-f1-8-ai-s/ Nikon AI-S 50/1.8 (Japanese pancake version)

https://richardhaw.com/2018/12/04/repair-nikon-50mm-f-1-8-series-e/ Nikon Series-E 50/1.8 (new version)

The lens you have is the AI-S pancake version for international markets. It is optically identical to the two models above and the mechanics probably share a lot of commonality with these lenses. Good luck with your efforts!

[rodeo_joe1]

I think the lessons to be learned here are twofold:

1) If it ain't bust don't fix it. 

2) Don't mess with a helicoid unless absolutely necessary. 

Not even a professional repairer takes a helicoid apart for the fun of it! Even if fully marked up and the alignment goes back together correctly, there's always a loss of grease in the process, together with the risk of 'grit' getting into the threads. Even normal house dust will degrade the smoothness of focus, let alone the danger of scratching or denting the fairly soft aluminium threads. The grease used is also a specialist product that has no common substitute. 

In short - leave helicoids severely alone! 

Also: A couple of specks of internal dust make absolutely no difference to a lens's image quality. And even if removed they'll probably be replaced with a couple more in a very short space of time. 

Edited April 5, 2023 by rodeo_joe1

[Incongruent Phonon]

2 hours ago, rodeo_joe1 said:

I think the lessons to be learned here are twofold:

1) If it ain't bust don't fix it. 

2) Don't mess with a helicoid unless absolutely necessary. 

Not even a professional repairer takes a helicoid apart for the fun of it! Even if fully marked up and the alignment goes back together correctly, there's always a loss of grease in the process, together with the risk of 'grit' getting into the threads. Even normal house dust will degrade the smoothness of focus, let alone the danger of scratching or denting the fairly soft aluminium threads. The grease used is also a specialist product that has no common substitute. 

In short - leave helicoids severely alone! 

Also: A couple of specks of internal dust make absolutely no difference to a lens's image quality. And even if removed they'll probably be replaced with a couple more in a very short space of time. 

”Not even a professional repairer takes a helicoid apart for the fun of it”

 

this is pretty much why i took it apart. Was waiting for my FM2n to complete the set. And i got awfully bored. Normally I have a couple things to do when im bored. But the lens gave me a good reason to mess with it : )

[rodeo_joe1]

12 minutes ago, Incongruent Phonon said:

And i got awfully bored.

Playing Sudoku, or taking actual photographs (good grief!) is much less destructive. 

[conrad_hoffman]

Good judgement comes from experience. Experience comes from bad judgement.

🙂

[orsetto]

Leave it to Nikon to go completely contrarian with this lens' physical engineering: as a bargain optic intended as an el-cheapo kit lens back in the day, you'd assume it would be fairly simplistic to disassemble. Unfortunately no: instead its the most convoluted Nikkor to service this side of an old pre-AI tele with "screwless" bayonet.

Based on what you've posted here (and Richard Haw's repair site), theres no way into the 50mm pancake glass package without a total teardown. This runs counter to nearly every other manual focus Nikkor I've owned: most of them have access slots on the rear element block allowing it to be unscrewed and removed without any barrel disassembly (use the proper tool or modify a drafting compass). With the rear block removed, you have easy access to clean haze-dust-fungus on that rear block. You can also open the exposed aperture blades to gain access to the inside front element block.

Most fungus or filth is found here in the exposed midpoint between front and rear groups. If you need to go deeper, the rear block is already removed making it more easy to open. But if something is trapped between the front elements you'd need to do the whole tedious front disassembly you accomplished here: if you're pretty sure thats the case don't bother unscrewing the rear group. Just go straight thru the front: with many common non-pancake non-floating-element manual Nikkors, the entire optical block cylinder containing front/rear groups and diaphragm lifts out in one piece from the front, leaving the helicoid undisturbed.

I've only needed to remove the rear bayonet when I wanted to update a pre-AI lens with a factory-original AI aperture ring conversion. Aperture ring swap is a pretty easy operation on the smaller lenses but can be a huge pain with the teles: I was confronted with an unexpectedly long and tricky aperture actuation lever/spring assembly when I updated my two Nikkor QC 135mm f/2.8 lenses.

The rear bayonet screws are often the biggest hurdle to clear on manual focus Nikkors. They're usually superglued to death, extremely resistant to loosening,  and the heads will strip into uselessness within seconds if you don't have a perfectly matched JIS screwdriver. Even with the right screwdriver, that thread glue is a nightmare to break thru, esp if the screws are the older slot head instead of the newer cross head. The cross head screws will eventually give way with the right screwdriver, but you are guaranteed to ruin at least one of the slot heads because nearly no screwdriver out there is a perfect fit for the damn shallow soft proprietary Nikkor slot heads. 

After a lot of trial and error, I settled on one of the "Husky" brand mini screwdriver sets with bits stored in the handle. One of the Husky cross bits is extremely close to Nikkor JIS spec, and one of the flat bits is a remarkably good fit for the shallow Nikkor slot heads (proper JIS cross drivers are available from Vessel etc but there doesn't seem to be an official JIS match for the Nikkor slot heads short of taking a time machine back to a Nikon factory circa 1971).