Disclaimer: I assume no liability for any loss or damage, direct or indirect, financial or otherwise, as a result of using these instructions. Use these instructions at your own risk and recognize that they are not factory authorized and may contain errors. Your lens may differ from the one described. Results will depend on your tools, skill level and judgement. Do not proceed if you do not have the experience to do this kind of work, and the ability to handle solvents and hazardous materials safely. Wear eye protection and comply with all local, state and federal regulations that may apply.
The 55 mm f/2.8 Micro Nikkor has been made in several versions. This write up is for the AiS version that began production in 1979. Other versions may or may not be similar. These otherwise excellent lenses are well known for becoming stiff and hard to focus, along with developing oily diaphragms.
The lens achieves its excellent performance through the use of a floating element. This element is moved with a second helical mechanism. When you focus a Micro Nikkor you're essentially focusing two lenses at the same time, and any drag caused by old thickened grease will be twice as noticeable. The finer half of the helical thread pair for the floating element is a close fit and has a lot of engagement area. Problems with old grease tend to show up there first.
Given the right tools and materials, the lens is actually quite easy to service. The only significant issue is correctly reassembling the second helical thread pair such that the element spacing is correct. I'll give you some measurements to insure this, but check your lens during disassembly to be sure it's similar to the ones I've serviced. If your lens has been incorrectly assembled at some point, there's a good chance that following these instructions will return it to satisfactory operation.
You will need a Phillips style screw driver that accurately fits the screws. Some will have been secured with thread locking compound and will be quite tight. The screwdriver must fit well so it can't slip and damage the screw heads or the lens itself. I've had good luck with the commonly available German Wiha screwdrivers, 261 series, PH00x40 and PH0x50, though there are special Japanese screwdrivers available from the specialty tool distributors that may be an even better fit to the Japanese screws.
You'll need a suitable grease. This can be a large and confusing topic, far beyond the scope of this write-up. The ideal grease will not harden or thicken with age. It will stay where you put it. The oil won't separate and contaminate the aperture blades. It will maintain a constant viscosity over a wide temperature range. The oil won't evaporate out and leave a film on the lens elements. Of course it would be nice if this unobtainable substance were easily available and inexpensive.
Almost anything that comes from an auto or home store will not be suitable. The finer helical thread is a close fit and most greases are too thick and viscous for it. Common greases are NLGI #2 and you really need a lighter #1. At the same time, the need for a light grease is probably the cause of oily aperture blades. The lighter greases tend to separate into oil and carrier, especially at higher temperatures. High temperatures also make outgassing and evaporation onto the lens elements more likely.
One of the main suppliers of precision lubricants is Nye Corporation. They don't sell direct in small quantities, but do list a small quantity supplier on their web site. Micro-tools sells camera repair supplies and also carries a limited number of Nye products. Their Nye 728J Rheolube grease looks like a good candidate for the Micro Nikkor fine helical, though I haven't tried it. I use Dow Corning Molycote PG-30L. This is a very light lithium grease with a synthetic PAO base oil. I don't know how easy it is to find, and you might have to buy it by the pound. Most other helicals can probably use Micro-tools 744 "helical grease".
If you can't get any of the above, people have had success with more common products. I would look for a Teflon grease, ideally with a synthetic base oil. Avoid silicones as they tend to creep. Avoid anything with a strong odor as that suggests volatiles that could contaminate lens elements. Though petroleum based, Slick 50 "One Grease" is a possibility. Kluber makes a wide variety of greases and is another source to investigate. Their high speed bearing grease NCA-15 has reasonable characteristics and is available from machine tool spindle rebuilders, but like most speciality lubricants, it's quite expensive.
If you have a small lab oven (don't use the kitchen!) you can do a couple of useful tests. First, put some of the candidate grease on a clean piece of glass, say a microscope slide, and set it vertically in the oven at 140F or so. After 24 hours use a magnifier to look for any trace of oil separation or creeping of an oil film away from the grease proper. Next, put a pea-sized glob of grease in a perfectly clean glass test tube or small bottle and cork or cap it. After 24 hours in the oven you can make a single swipe on the inside with a Q-tip and clean solvent. Inspect with a bright light and magnifier. If the Q-tip leaves a clean trail on the glass, with a surrounding haze, the grease is probably outgassing. This test is somewhat difficult and sensitive, so run a control tube with no grease as a comparison. These tests aren't quantitative, but should let you pick the better of two greases, and might weed out the really bad ones. Seriously, all this should suggest that a sane person would just order a suitable grease!
Be sure to have a clean work area and lay things out neatly. You'll want some lens cleaner and lens tissue, a large ear syringe to blow off dust and maybe some small containers for screws and parts. You'll also need some cleaning solvent that's effective on the old grease. You want to begin with the least aggressive and hazardous solvent that will get the job done. That's probably lighter fluid or mineral spirits. If the grease is very stubborn, Toluene (toluol) is effective but rather hazardous. I use this outdoors or in the garage only. It will damage plastics and painted surfaces, both of which are found in lenses, so extreme care is necessary!
Let's begin!
We'll start with some specific settings on the lens. This will insure that the internal parts are in specific positions. There is nothing special about these settings; they are just the arbitrary settings where it was convenient to measure certain dimensions you'll need later. Set the aperture to f/8 and the focus to 3 feet as shown above.
Remove the three screws holding the mount to the back of the lens and lift it straight out.
The automatic aperture arm is very long on this one, as it has to accommodate the long focus travel.
The entire lens module is held in by the three screws shown. Note that during reassembly the slotted screw head to the left of the upper mounting screw must fit in a close fitting notch for everything to seat correctly. Remove the three screws and maneuver the module out the front.
You'll have to tilt it slightly to unhook the aperture tab from the big slot shown at about 2 o'clock above.
Now is the time to check your lens module to confirm that the dimensions are very close to those given here. For the 3' focus setting asked for above, the anti-rotation tab should be about 1/3 of the way across the slot. The gap shown in the middle should be about 0.025" wide. The surface of the brass ring with the tab should be just about even with the edge of the housing as shown by the arrow. This is our reference position and errors during re-assembly will be very obvious on comparison. If your lens is different, be sure to record and use the original values for reassambly! As far as I know, and as long as the brass ring hasn't been removed or come loose, there are no subtle or non-obvious errors to worry about. If, on reassembly, your lens module is close to the conditions given (or the ones you recorded), you're good to go.
The aperture assembly is held by the three screws shown above. Remove the three screws and lift off the aperture assembly and its associated lens.
We're nearly there! Remove the two screws holding the anti-rotation tab shown above. Be sure the screwdriver fits well as they will be tight and thread locking compound was used. Lift out the anti-rotation tab with tweezers.
Unscrew the three components. The finer thread is left handed. Do not remove the brass ring! Disassembly is complete, so it's time to talk about cleaning and re-lubrication.
The two threaded barrels on the right can be immersed in solvent. I like to use an ultrasonic cleaner, but a small brush or piece of rag will work. Avoid contact with the solvent. When clean and dry, apply a thin film of grease and screw the two pieces back together. Wipe away any excess grease and be sure they move freely. This is the location where a thick or viscous grease will create a lot of drag.
Obviously you can't immerse the lens element on the left so use the edge of a folded piece of paper towel to clean the threads. Be sparing. Do not get any solvent on the lens elements or let it seep into where the parts are screwed together. Don't get any on the painted front portion of the barrel.
Now comes the only tricky part of this whole procedure, and it's not really very tricky. The coarser thread is a two start thread. That means it can go together two ways, and only one of those ways is correct. Apply a thin film of grease and screw in the remaining barrel. Adjust the assembly so the brass ring is even with the housing and the gap described earlier is about 0.025" wide. Now, look at the location of the mounting holes for the anti-rotation tab. If they are close to lining up with the slot, you're good to go; reinstall the anti-rotation tab. Be sure it has the countersinks for the screws facing up.
If the mounting holes are about 180 degrees away from the slot, you need to restart the inner barrel that carries the lens element. Unscrew it and rotate it 180 degrees from where it just comes apart. It may take a few tries to get it together, as multi-start helicals are often hard to get started at all. Keep at it and don't force anything. This is no place to be heavy handed. You only need to get it started correctly once. When you have the anti-rotation tab installed, rotate the brass ring back and forth to check for reasonably easy motion and that the gap is correct when the ring lines up with the housing.
Reassembly is now just a matter of reversing the steps above. If the aperture blades are oily, the lens assembly must be removed and everything else cleaned and dried. Even if the blades are clean, inspect the frame and clean off any oil that might have migrated to the surface. That oil is trying to get to those blades! Do any necessary cleaning of lens elements at this point as well.
I haven't addressed disassembly and cleaning of the main focusing helical. It's usually far less of a problem and I've yet to take one apart. If it seems to be getting stiff (and even if it isn't) I'd suggest applying a drop or two of a good synthetic oil to the threads. That will mix with the grease and restore normal operation. I use Break-Free, a high grade oil with some Teflon additives, often found in the sporting goods section of your local discount store. Extend the focus and be sure to lube both sides of the helical. Cycle it a few times. This trick is reasonably safe, as the path to the aperture blades from the main focusing helical is reasonably long. Still, inspect the main focusing helical before reinstalling the lens module and be sure there is no excess lubricant, especially oil, that can run down near the back end of the lens and find its way to the aperture mechanism.
If the focus is set to 3' and the lens module is as described above, everything will be very close to sliding together. The tab on the brass ring must engage with a slot, so it might be necessary to rotate the focus ring slightly. The assembly will normally drop in quite easily. I don't re-lacquer the screws, as it's more of a tamper indicator than protection against loosening. Reinstall the mount, check that the auto-aperture works freely and the lens should be good for another couple decades.
For reference, the front section of the focus barrel unscrews just underneath the front of the rubber grip. This gives access to the slots and locking screws to adjust the infinity focus point. The front of the barrel may be quite tight and it is strongly recommended not to make this adjustment unless absolutely necessary. The factory will have set it correctly, and unless the lens is extremely worn or previously disassembled, it should be correct when the lens is reassembled.
Conrad R. Hoffman
4/16/2010
Additional- The lens illustrated above is s/n 537xxx and I've also serviced an identical s/n 572xxx. I recently serviced an earlier s/n 195xxx Micro Nikkor. The earlier lens used a slightly different auto-aperture mechanism on the lens mount, but was otherwise identical. All dimensions and procedures matched the above write-up. The older auto-aperture mechanism doesn't include a return spring and is prone to rattle, which is of little consequence. The grease in the focusing helicals was OK, but the lens had the well known oily diaphragm problem. It appears the source of oil may not be either helical, as I originally speculated, but migration of factory applied oil from various aperture parts. The easiest way to clean the aperture mechanism is to remove the lens elements from one side, making careful note of the curvatures and the direction they face, then soaking the rest of the mechanism in Xylene or a similar solvent. Gently cycle the aperture when completely wet with solvent, then allow it to dry. Never try to move an aperture that isn't completely wet (submerged) or that shows any resistance, lest the blades be damaged. It's hard to get shutters and apertures dry- be patient. Only use an air blast from a foot or so away, as the blades are fragile. Apply a the tinyist film of grease to the actuation cam and reassemble.
Aperture and shutter blades are never lubricated, but the surrounding actuating mechanism, especially on shutters, usually is. I don't know if the Micro Nikkor aperture mechanism should be oiled or not. Speculating, if the lens were used at high frame rates for a long period of time, lubrication might be critical. You'd want to fully disassemble the mechanism and evaluate what points needed lubrication. For normal applications it's probably not an issue. The downside of oil is that it migrates and may eventually contaminate the aperture blades. It's also a temporary measure and a lens seeing high frame rate use should probably be serviced every couple years. Cameras and lenses used in that manner will wear out and fail; fortunately almost no amateur equipment sees that level of use.