Serv(ic)ing A Micro legacy: Micro Nikkor-P Auto 55mm f/3.5

The Micro Nikkor 55mm f/3.5 series of lens has had a long history with the first iteration arriving in 1961 and lasted nearly 20 years with the same optical formula, cumulating in the Micro Nikkor 55mm f/3.5 AI. Of course, the 55mms prior to the AI version were all pre-AI although Nikon provided factory AI aperture ring conversions and its reasonable rare for still find a pre-AI factory converted 55mm. I found a late edition (1969-73) factory converted P-Auto and give it a service and here's what I found.


^{Micro-Nikkor P Auto 55mm f/3.5, with factory AI conversion and non original rubber grip}

Servicing

As a pre-AI lens you will unpleasantly find that the screws are all of the slotted variety, and lacking any form of uniformity. The lareger screws are different: the 5x rear mount screws are one size, as are the 3x helicoid keys and this goes on to the 3x distance sleave compared to the 3x focus ring screws and of course varying levels of glue are applied: patience and heat are your friend here.

Whilst this is a P-Auto version - based on nameplate and the 713xxx serial number my copy shared the same mechanical internal structure as the PC Auto as opposed to the P-Auto - this was evident with the 3x helicoid screws.

A grub screw'd front retaining colar needs to be removed before revealling the optical block which can be picked out first - this houses the frist element and the glued doublet.

The rear mount should be removed next with nothing to trip you up. The aperture ring is secured by a single (long-ish) screw which slots into aperture fork ring.

Reset the focus to infinity to give yourself a known working point. Remove the rubber focus ring and examine the 3x screws underneath - mine were covered in glue and a couple were stuck. Ensure that you use the right driver with a suitable length to make removal much easier; apply heat if needed. With the focus ring out the way, mark the infinity position.

Next, find another (smaller) driver for the the 3x distance sleave screws - mark on the rear helicoid the infinity position for reference so you know how to reseat this distance sleave later. Remove the screws and slide to the front of the lens to remove. After this is removed (and along with the aperture ring) you now have access to the 3x helicoid screws.


^{3x helicoid screws - notice the aperture fork ring and the slot for the aperture ring screw. ignore that the focus ring / distance sleave are still in place at this point}

The helicoid screws are glued and they are an utter pain - those screws want to be stripped and its imperative that you apply heat to soften whatever glue was applied - I used a hobby heat gun that was pointed directly (milimeters away) at the screws and left the heat gun running. With gloves, work on one screw at a time to break the bond and get some movement. I had to do this multiple times on each screw - a soldering iron didn't work for me. Without removing the helicoid key, note how far the helicoids run down the key - almost at the end.



Remove the helicoid key and do the usual - hold the rear helicoid still and slowly turn the central helicoid to remove, and mark the seperation point on the central helicoid relative to the infinity mark on the rear helicoid. Similary, do the same for the inner helicoid, holding the central helicoid with the infinity reference mark visible and mark the speration point on the inner helicoid relative to the infinity mark. Go and clean with the usual lighter fluid and IPA - I found the grease to be incredibly bad here, very viscous and sticky.

Once clean and ready, a light application of JHT#10 was applied to the shiney surfaces of the aluminium innner and the central helicoid when they were ready for re-mating. I always remate the inner-to-central first and then inner-to-rear last.

Reassemble and test the feel of the focus throw, ensure that it is not too heavy. The reseating of the helicoid key needs to be exact as there is tight tolerance and snaps into place - ensure that you grease the helicoid key. I used a heavy NLGI #2 rated lithium grease for this.


^{fully assembled sans lens objective - it is sometimes easier to insert the lens objective first (catching the aperture fork) and then the rear mount (catching the aperture activation fork from the rear)}

Optics

Its relatively simple 5/4 optics aren't too painful to service.





The optical block has 2x logical blocks. The front requires rubber cones to separte. To get to the first element you will need IPA/accetone to remove the nameplate and then thin lens spanner to open (its very tight). At the rear this can be twisted off with cones after more IPA.

Performance

The usual exposure factor applies so care is needed for exposures



Given that the Auto-P and the AI share the same optical formula, sans differences in lens coating, they perform near identical. Wide open and at MFD giving a 1:2 reproduction ratio the lens is, like its younger sibling, sharp and already has great detail.


<sup>centre crop at MFD @ f/3.5


@ f/3.5</sup>

Final Thoughts

If we copmare the Auto-P and AI lenses, they are almost identical: same optics, same focus throw (300degrees) and comparable size (66.5mm vs 66mm diameter) and weight (235g vs 245g). There isn't anythign to choose between them - given that Z-series/FTZ adapters do not have an AI-coupling tab, this means either is good for your Nikon mirrorless. With Nikor F-mount bodies you will have to choose the AI version unless you are lucky with an AI aperture ring (factory or otherwise). But both are equally nice to use but I do find the Auto-P to be a handsome lens and that might be enough for some to choose between them.