Nikon 50mm f/1.4 Ai Disassembly and Cleaning

Nikon Df and the cleaned 50mm f/1.4 Ai

Return of an old friend

I have always had fond memories of the days with just the humble standards lens, a Canon FD 50mm f/1.8 SC on Canon AE-1 that I borrowed and used for a good 2 years.  The 50mm lens taught me a lot about photography, having large aperture and “normal view” I learned quite a bit of photographic techniques in my formative years.

Sometime in 1986-87, I bought a used 50mm f/1.4 Ai which then became part of a 3-lens combination of 28-50-105 that served me very well for many years.  It was later sold, to make way for the AF version of the same lens.

This lens was purchased as a set with an F2S at the local junk yard.  The F2S would require the work of my good friend Hilos Camera Repair to bring it back to full specification again.

50mm f/1.4 Ai – a lens with character

In a way the f/1.4 normal lens is the flag bearer of many marques, being in the normal lens range (43mm being the diagonal of 35mm film) it is relatively easy to design and built, and is the cheapest f/1.4 lens available for any brand.  We do usually have to stop down a stop or 2 to get really good results, but I had often found myself pushed to the f/1.4 limit during my film days.  It is often said that all photographers should own a 50/1.4 or 1.8; such is the value of the normal lens.

Optically this lens shares a common design starting with the non-Ai Nikkor K second version (slim), through to the Ai, AiS, AF and AFD versions.  Prior designs include the 5.8cm f/1.4, and the 50/1.4 Nikkor-S, SC and K versions.  Adding the AFS version there are 4 optical versions of the 50mm f/1.4.

Optical Performance

I am not a brick-wall shooter, not too interested in technical aspects of the lens.  So with the Nikon Df in hand, and the cleaned lens, I went out and did some casual shooting for the purpose of showing some day-to-day type of shots.

Fallen comrade.  At f/1.4, there is discernible light falloff (vignette), and softness to the edges, with an adequately sharp centre.  Nikon Df, 50mm f/1.4 Ai, 1/250s f/1.4 ISO 100.

Mural: samsui woman.  Samsui women, also known as hong tou jin (红头巾; Mandarin for “red headscarf”) after their trademark red headgear, were female immigrants mainly from the Sanshui (“Samsui” in Cantonese; meaning “three waters”) district of Canton (Guangdong today) province in southern China.  Samsui women started arriving in Singapore in large numbers in the mid-1930s and many found work as general labourers in the construction industry.  Reference: http://eresources.nlb.gov.sg/infopedia/articles/SIP_795_2005-01-18.html.  At f/2, I find the lens adequately sharp and exhibits little light falloff.  Nikon Df, 50mm f/1.4 Ai, 1/50 f/2 ISO 2000.

Mural depicting life in Singapore in the early immigrant days under British rule.  You can see the Chinese working as labourers (“Kuli”) and having shaved foreheads and wearing a pigtail, required under Qing Dynasty that ended in 1911-1912.  My family arrived here between 1890-1910, no way to know for sure which year.  Nikon Df, 50mm f/1.4 Ai, 1/80 f/8 ISO 100.

About me

I am an engineer by training, I enjoy photography, love listening to music, and am addicted to scuba diving; hence the nick diediemustdive.  You are here not to read about me, but about the lens I am about to describe, but then you just might be interested to know a little more About Me.  Go ahead and click on that link, if you will.

Before we begin…

Disclaimer: all information in this blog is meant for sharing of experience and not as instruction, and is no substitute for diligent learning and assessment of competence.  I have messed up my fair share of lenses, and will not be held responsible for any damage caused in the reader’s venture into this fascinating world of mechanical and optical marvel.

You should be conversant with lens repair techniques; beginners should read my earlier blog posts – the Lens Repair series, and Richard Haw’s excellent write-ups (Camera and Lens Repair Essentials, Best Practices (part 1), Best Practices (part 2), Best Practices (part 3) and Working with Helicoids).

Optical and Mechanical Design

 

Optical Design: 7 elements in 6 groups; the optical unit (OU).  Always useful to have the optical design, as it aids reassembly in case the markings get smeared!

There are mechanically several Ai and 1 AiS versions.  This is the final Ai version, with 3(+) bayonet mount screws and 2 aperture ring (AR) aperture coupling screws.  The version without the 2 AR aperture coupling screws has a ring with a protruding screw to couple with the AR.  See reference (in Japanese – look at the photos).  If your lens is without the AR aperture coupling screws, you will need to work around this and not follow this post strictly when working around the AR.  The pre-Ai versions have a spring at one of the screws at the mount – which is not a mount screw and that screw should not be removed.  I believe the clue to this is the index being a line rather than a circle.  The first K version (much “fatter” lens) also has this screw and spring, as did the Nikkor-S version.

Mechanically, the lens main components are (coming from the front, and inside out): OU retainer, OU, OU helicoid, focusing ring (FR) helicoid, barrel (with helicoid), FR cover, FR, chrome grip, aperture ring (AR), bayonet mount.

OU retainer, OU and the lens body.  Note the slot on the OU helicoid and the screw – they form the alignment between the OU and the OU helicoid.  Just within sight at the bottom is the OU aperture coupling lever – the position of which must be marked in this version of the lens in order to return the OU back to the body.

I was not able to find an exploded diagram for this lens.  Although I did find one for the 50mm f/1.4 AiS, the mechanical construction is too different to be of any use.

Disassembly – Mechanical Components

Set aperture at f/16, focus at MFD, and locate set screw.  Remove set screw and unscrew the OU retainer.

Gently tab the lens and the OU should slide out.

In the Ai version with 3 (+) bayonet mount screws and 2 AR coupling screws (as in this example), immediately mark the position of the aperture coupling on the OU.  Set the OU aside for later optical cleaning.  If you have no mechanical or aperture issues, you can skip to the optical cleaning part of this post.

Remove the 3 (or 5) screws holding the bayonet mount.  My experience has been there is at least one screw with thread-lock applied.  I fear this screw, for I have had rounded quite a few screws in my time.  The use of JIS screwdrivers is essential – make sure the screwdriver fits the screw tightly, so that when force is applied the screwdriver head will  not slip!  Proceed with firm downward force while attempting to turn the screws; and at the first sign of significant resistant desist.  Acetone treatment is then necessary.  My friend David can simply apply firm down force and provide sufficient torque to break the thread-lock; I can’t.

In this version of the lens there are 2 screws holding the aperture coupling to the AR.  In the other version, I think, the AR can be lifted up immediately.  There is then a ring that couples with the aperture lever.

The AR aperture coupling lever.  Press this with your fingers while removing the 2 screws.  Remove the AR.

Gently remove the rubber grip to access the FR cover.  This rubber is likely to be brittle and it is easy to rip it!  I ripped this one; first one thus far.

Locate the drip hole and apply a few drops of alcohol into the hole, wait a short while (maybe a min), and with friction grip gloves, remove the FR cover.

There is a shim with 3 screws holding the FR to the FR helicoid.  The broad piece of dark coloured metal is the helicoid key.

Note: photos below were taken after servicing was completed.  My initial disassembly was less organized, and I had to trial and error to find the correct alignment of the helicoids.

Important: if you have to work with the helicoid, and you see a blog post that has no description on the alignment marking, be very weary as failure to note how the helicoids separate/couple will result in endless trial and error to find the correct point of coupling!

Take several photos at this and at every stage, you may need them to figure out the alignment.  I had to use the early photographs to do just this, and the adjustment process was very painful!

To recap, with the helicoid key in place the OU helicoid moves the OU in and out on the optical axis without rotating the OU when the FR is turned.  The FR couples with the FR helicoid via 3 small screws and a shim.  The chrome grip part extended towards the front (see photo below) is the stopper in the present case – look at the focusing ring and you will see on the inside there is a small part that will stop the FR at both infinity and MFD.  There needs to be a barrel helicoid to let the FR rotate helicoid in the barrel.  This way the filter ring will not turn; a simpler design will have a pair of helicoid, with focusing ring coupling to the OU helicoid, and the OU helicoid will rotate in the barrel helicoid.  That way the filter ring will turn, as in most zoom lenses and a few prime lenses.  See my posts on 36-72/3.5 E and 80-200/4.5 C for examples.

Turn FR to infinity, remove the 3 screws and then the FR.  Mark the infinity positions of the OU helicoid (inner most tube), FR helicoid (black ring) and infinity on the barrel helicoid.  Remove the helicoid key (2 screws on the barrel).  This frees up the OU helicoid.  Ensuring that the FR is not moved, rotate the OU helicoid counter-clockwise (CCW, blue arrow in photo above)， count the number of turns, and watch for the point of separation, mark point of separation.  Rotate the FR CW (red arrow), count the number of turns and watch for the point of separation, mark point separation.  These points of separation is where you will re-couple the helicoids.

From left (photo not in the usual orientation – now front is to the right!): barrel body with helicoid (chrome grip attached), FR helicoid and OU helicoid.  The grease on the helicoids had dried up / gummed up and the FR was beyond stiff!  After separating them (and removing the chrome grip) the helicoids were cleaned using lighter fluid.

The complete disassembly (OU intact here, AU and the rear mount assembly (ball-bearings included!) not disassembled).

Optical Cleaning

 

The optical unit (OU 7/6), comprising the front OU (3/3), aperture unit (AU) and rear optical unit (4/3).

Front view: fungus is evident.  Remove the name plate (which acts as retainer to E01) with a rubber tool, then open the retainer to the front OU with a lens spanner.

Mark orientation!

Name plate, E01, front OU, AU.

Side view of the front OU; hole indicating that alcohol may be necessary to remove this retainer, which turned out to be the case for E03.

Front OU completely disassembled.  Top row: name plate, E01.  Bottom row: front OU casing, E02, and E03 and rear retainer.  I proceeded to clean E03, then E02, return E02 and E03 to the casing, then E01, and close up the front OU with the name plate.  Hydrogen peroxide to kill the fungus, the clean with alcohol, both from a local pharmacy.

E02: I was told this type of “frosty” mould would destroy the coating, and sure enough on close inspection after cleaning there were coating impacts.

Rear view of OU.  It is clear that the fungus has infected internal elements as well.  The “hairy” mould is less damaging.

Apply a few drops of alcohol into rear OU holes and at the adhesive mark area, and unscrew the rear OU from the OU casing.  Two slots on the front view of the rear casing – use lens spanner to open the retainer, set E04/E05 aside.

Internal view of E06: another pair of slots to open up the retainers using lens spanner.  E07 is within the rear OU case.  Again the same procedure, clean E07, then E06, place E06 back into case and tighten retainer, clean E04/E05, place E04/E05 back into case and tighten retainer.  Return rear OU back into casing.

There was no problem with the aperture blades, so I left the AU alone.

Re-assembly

Re-assembly essentially followed the reverse procedure.

• Return FR helicoid to the lens barrel – align at the separation point and return the FR helicoid to the barrel helicoid, to the marked infinity position
• Return OU helicoid to the lens barrel – as above align separation point, turn to marked infinity position
• Fix the helicoid key

• Return the AR to the lens barrel, fix the AR aperture coupler
• Return the bayonet mount to the lens
• Carefully set the alignment of the OU aperture coupler to the marked position and return the OU to the lens (cleaning of the optics assumed completed, see optical cleaning section). This step can be very tricky for the 2-screw AR coupler version.
• Return the OU retainer to the lens
• Adjust for infinity focus
• Remove the OU retainer, and reattach the FR, then the OU retainer

Note: I had removed without getting all the separation marks done correctly, I had to trial and error to get the helicoids aligned.

Adjust for infinity by the process below.

Adjusting for infinity focus: attach everything except the FR, and attach the lens to a camera.  Rotate the FR helicoid to get infinity focus, then re-attach the FR base on this position.  You will likely want to remove the OU retainer when re-attaching the FR (space to work the screws).  Be careful when the OU retainer is out – you can drop the entire OU and have a very expensive accident!

The lens after cleaning

Not too bad!

Conclusions

As anticipated, this lens was relatively easy to service, even though I did have some reservation about going to the helicoid, especially in this case where the almost stuck helicoid made it difficult to mark alignment.  But having played with helicoid alignments a few times with various zoom lenses, a Yashica 50mm f/2 ML and a Ricoh 50mm f/2 XR, I had some practise and was able to navigate through this lens.  The focus is now smooth, but not buttery smooth, as I did not do a very thorough helicoid clean-up.  Someday I may!

I have thoroughly enjoyed disassembling, cleaning and reassembling this lens, and am enjoying the company of an old friend.  Most of all, rescuing a lens from the junk yard and restoring it to as close to its former glory as I could, is satisfying.  What was imperfect?  Some coating damage, and helicoid smooth but not buttery smooth.

References

50mm f/1.4 Ai – focus on the helicoids with good photos to illustrate process for 3+ screws 2 AR aperture coupling screw version, with a photo to show the version without the coupling screws, in Japanese Aiニッコール50mmF1.4の分解 http://www17.plala.or.jp/rec-c/sub3.html

50mm f/1.4 Ai – complete disassembly – with good photos to illustrate process, in Japanese 修理人たぐちの徒然日記 Ai NIKKOR 50/1.4 編 http://www.kitamura.jp/photo/repairer/2013/re940.html

50mm f/1.4 Ai – optical part only, in Japanese, Ai NIKKOR 50mm F1.4 分解清掃 http://dracame.exblog.jp/20900193/

50mm f/1.4 Ai – Cleaning aperture blades レンズの分解清掃 – http://www.geocities.jp/pxm0/nikkor50mm.htm

50mm f/1.4 Ai – Nikon NIKKOR 50mm 1:1.4 Cleaningしてみたよ (Youtube) https://www.youtube.com/watch?v=1xLSVCIChLU

50mm f1.4 Ai partial disassembly to show the difference between the “usual” construction of the 50mm f/1.4 Ai and the 2 AR aperture coupling screws version), in Japanese.  Ai Nikkor 50mm F1.4の内部構造が違っていた件 http://gossan.cocolog-nifty.com/blog/2010/02/ai-nikkor-5014n.html

50mm f1.4 Ai Disassembly (erroneously labeled as AiS, version with 2 AR aperture coupling screws, same as my blog post, also omitted helicoid alignment part – dangerous to follow this blog!)  – dehk – https://dehk.wordpress.com/2011/02/01/ais-nikkor-50mm-f1-4-disassembly/