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Several months (probably closer to a year) after purchasing a secondhand Nikkor 28mm f2.8 AF for quite a reasonable price off fleabay I noticed some quite random stuff going on with the exposure, I finally tracked it down when peering through the rear element and playing with the stop down lever. Each blade, at the contact point with the next mating blade had a fine dark coating which could only be described as an oil problem! Some internet related research did not yield a huge amount of info but did lead me to believe that oil on the aperture blades was fairly common for this lens, one interesting piece of information I found was that one should store this lens face/ass down to prevent oil from flowing onto blades, at this point I thought wtf.. that 'ain't good enough.
I found that giving the stop down lever a good workout before using the lens made it quite usable and the blades fairly responsive, this finally died in the rear when the blades finally stuck in the open position (f2.
and only stopped down to f22 over a period of a few hours... So, what to do, flog it off on fleabay again? Take it to Nikon Australia? well I would not do the dodgy and pass it off to fleabay and the thought of paying more for a clean and quote fee from Nikon Australia then what I paid for the lens to start off with lead me to the only reasonable conclusion (jilted logic ya gotta understand!) - pull it apart and have a look! Whats the worst that could happen, I am left with a paperweight...I can live with that.So a bit of research on the web for info on this aperture oil problem and also the option of a self clean yielded quite a number of resources dedicated to the old skool Ai lens but very few for the AF series lens. There was even a few flickr sets on a guy who had re-greased the helicoid on a 50 f1.4 AI. A couple of worthy sites came to the forefront and are deserving of a mention (excluding flickr):
Microtools! - I did not buy anything from here, however they seem to have all the goodies for the hobby camera/watch DIY.
Lens-inc - Lots of manuals and Exploded Parts Drawings
Besides the obvious concerns of damaging something during the disassemble or not being able to re-assemble the primary concern was what to use to clean the aperture blades and re-lube them (if they needed it, graphite maybe?) I did track down a parts manual from the Lens Inc site above for the 28mm and for 6 bucks aussie it was well spent in my opinion. However it does not have any details on lubes or procedures. It does have however, a very tidy selection of section views of the lens - these are great to see how it looks when assembled. A word of warning though, if you have never looked and understood a proper section view then its just gonna look like a whole bunch of useless lines on a page to you
So onto what I did:
Tools used:
Decent set of screw drivers, none of this 2 dollar shop sh$t, you need a good sturdy Cr-V steel tip set. Stainless steel tweezer set which is very essential (keep those grubby hands off the important bits). Surgical razor blade - many uses including cutting sticky tape
Consumables: Isopropyl Alcohol, Pec Pads, cotton wool buds, double sided tape, sticky tape (probably should have some of that 3M non residue stuff and a small bottle of scotch or jager.
Words of Caution - This is purely a record of what I did and my experience, I do not any any way condone or recommend this to anyone. Also expect no warranty to these steps, do it at your own risk.
More words of caution:
- if you 'round' a screw head on these things it's good night. Most of the screws have a thread locker of sorts, not a true thread locker like Loctite but more of a tamper seal (clear red adhesive) placed on the head of the screw. Firm, perpendicular force is required to remove each screw.
- Protect the exposed lens elements where ever possible, a slip of the screw drive and thats a big scratch, a pec-pad may not prevent this but will help in any case.
Be prepared to disassemble and re-assemble more than, say twice (3 times in my case), I forgot to put the little aperture lock switch spring back in on the first go, the second go I got it horribly wrong and the internal lens was half a revolution out which resulted in the lens not focusing at infinity (good one toolie), third time lucky and it was all good.
I basically went hell-for-leather and started at the back and removed what ever screw i could get too, some thought and access to the IPC (Illustrated Parts Catalogue) would have been smart here. Prior to going hard at all the screws I attached a pec-pad to the rear element for some protection. It does get fairly self explanation once you get the rear mount off and the aperture ring, I also made sure I remembered what screws went where and how many, they are typically all different sizes and lengths, so not interchangeable. If you are planning to do it over a period time (ie days) use sticky tape to group screws to their locations - I found this very useful, probably would have worked it all out anyway but it saves time.
In hindsight, the order of disassembly and also the amount required would be different, but since this was a first crack I was not particularly fussed. The whole lens does not need to be disassembled to get the len element assembly out. Basically once you get the 'L' brackets (2 off) out the lens element will rotate out.
1) Remove the electrical connector/plug screws (qty 2), rotate the aperture ring around to get easier access to these tiny screws. These are the smallest screws used in this lens, make sure your screwdriver is appropriately sized. Remove the 3 screws holding the black plastic (matte finish) shroud that surrounds the rear lens element.
2) Remove the 3 screws holding the metal adapter that interfaces with the camera.
3) Now one can remove the black shroud (leaving the electrical connector in place) and the mounting adapter, things should be looking like this...
4) Remove Aperture ring and spacer plate, this plate is quite important since it engages the aperture ring with the aperture lever, if it is not correctly placed your aperture ring rotates without moving the aperture!
Spacer plate, aperture ring and mount;
5) Remove screw drive sprocket now cause it will fall out otherwise, also during this the aperture ring lock switch falls out, remove that too. There is also a little bent piece of spring steel which sits behind the switch, do not lose this bit - I almost did.
6) Release the two 'L' shaped brackets which basically keep the lens aligned when moving forward and aft in the lens body, after these are removed the front/aft lens assembly will be able to be unscrewed out of the lens, but wait until the next step is complete before trying this. Remember the position of the lens before taking these brackets out, it is possible (i did it) to not screw the lens all the way back in and hence the whole lens is out by half a revolution.
Righto, so things should be looking like this, arrange things as the come out, especially if you have a memory like a fish...
7) Remove the lens (front and rear assembly) from the body of the lens.
8) Remove the lens cap and apply double sided tape (small 1/4" bits) to the bezel (with the AF Nikkor logo), apply them all the way around the bezel. Using the rear lens cap reversed, place this on the bezel (and tape) and ensure its adhered. This will then permit one to rotate the bezel (anti-clockwise) off. This is essential since it then gives one access to the three screws that hold the front element in. Only a exploded parts view and section view will tell you this since that bezel hides all
9) Remove the three screws that hold the front element in and take that baby out. protect suitably with pec pads etc. This leaves the aperture assembly visible, woohoo.
10) The gold coloured retaining ring is held in with 3 screws, remove those and then the ring. The ring is also bonded in place (on the outer two tabs).
Note: This is where it becomes evident where the oil is coming from, the retaining ring sits in two slots (where the outer tabs mate) in the body of the lens assembly case, these slots pass right through to where the helicoid is. The oil, or rather grease has wicked down through this slot. In hindsight one should use adhesive to fill this slot (its only 0.005" wide) to prevent this problem from occuring again (possibly this is the Nikon permanent fix I have heard about). Really the design should have not permitted that slot to pass all the way through the plastic body, rather just a small recess, just enough for the tabs, thus, making the lens element area completely closed from the aperture blade area. But, its always easy in hindsight
and manufacturing limitations may have dictated this.Grease on the Helicoid and location of oil entry into the aperture blade location
11) Remove the Aperture assembly, there is a little spring that holds the aperture closed, this needs to be released, there is then a plate on the aft side of the assembly that links all the blades together, this will probably fall off and copious cursing will follow - it did for me.
Little spring:
12) Clean all blades gently in isopropyl, also the body as well and the retaining ring and the inside of the body. Also the area where the grease was seeping in! I used multiple cotton wool buds.
13) Reassemble aperture assembly, this is tricky, Make sure the blades are placed one on top of each other, with the final one the placed back over the first - a bit like when you fold the 4 flaps of a box lid up! This is important, the blades will not operate correctly and will probably crash and fall out when you try turn the whole upside down if the blades are not arranged correctly. Also do not operate the aperture until its back in the body, opening it up may mean it all falls apart...again.. It took me a few goes to get it right and learn the process.
14) Reassemble the whole thing
Cleaning and removing dust as you go!Clean aperture blade..oh sooo snappy!
Reassembled:
OK some images - before the clean:
After the clean and partial re-assemble:
oh yeah, by the way, it works like a bloody charm now...
