The Micro 105mm f/4 AI is larger than the Micro 55mm f/3.5 AI and the 105mm f/2.5 AI-S even if its feels lesss dense than the latter, with handling on modern bodies is comfortable. When the lens is fully extended its in the ballbark of a 24-70mm f/2.8G or 180mm f/2.8 ED AI-S.
Micro-Nikkors 55mm vs 105mm | 105mm f/2.5 AI-S vs Micro-Nikkor 105mm f/4 AI
Whilst the 105mm micro focuses down to 4.7cm for a native 1:2 reproduction ratio, it requires 1.6 stops of exposure compensation whilst distances no closer than ~1.3m (providing 1:10 reproduction ratio) does not. The following table summarises various focus distances and reproduction ratios.
| Lens | Minimum Focus Distance | Reproduction Ratio (at MFD) | Minimum Focus Distance (no exposure compensation) | Reproduction Ratio (no exposure compensation) |
|---|---|---|---|---|
| Micro-Nikkor 55mm f/3.5 AI | 2.41 cm | 1:2 | ≈ 0.7 m | 1:10 |
| Micro-Nikkor 105mm f/4 AI | 4.7 cm | 1:2 | ≈ 1.3 m | 1:10 |
| Nikkor 35mm f/2 AI | 30 cm | ≈ 1:5.7 (0.175×) | ||
| Nikkor 50mm f/1.8 AI / AI-S | 45 cm | ≈ 1:6.7 (0.15×) | ||
| Nikkor 200mm f/4 AI | 2.0 m | ≈ 1:7.4 (0.135×) | ||
| Nikkor 80–200mm f/4.5 AI | ≈ 1.8 m | ≈ 1:7.4 (0.135× at 200 mm) | ||
| Nikkor 180mm f/2.8 ED AI-S | 1.8 m | ≈ 1:7.5 (0.133×) | ||
| Nikkor 105mm f/2.5 AI-S | 1.0 m | ≈ 1:7.7 (0.129×) |
(c) Nikon - from 105mm user manual, TTL Compensation values
Using the micro 105mm in non macro applications (ie portrait) is fine - when compared to the 105mm f/2.5 AI-S at f/4 (which is incredibly sharp at f/4) the macro lens does a reasonable job with more micro-contrast and feels clinical and I think I'd prefer the f/2.5 AI-S. At macro or near distances, even wide open, resolution and sharpness is already very good with perhaps some CA/fringing.
centre crop, near MFD, f/4
centre crop, near MFD, f/5.6
centre crop, near MFD, f/4
centre crop, f/4
For fine detail, such as surface scratches on coins, wide open does lack some contrast but its not bad. Stopping down one stop improves this.
f/4 - coins, 10cent HKG coin is 17.5mm in diameter
f/5.6
Coin Imaging's tests of the 105mm f/4 AI-S (same optics) conclude that f/5.6 is the aperture with highest resolving power although f/8 is the sharpest. I find that at non-macro distances contrast wide open is low and much better from f/8. I find the 55mm f/3.5 AI to be sharper and Coin Imaging's data backs this up.
(c) Coin Imaging
At general/non-macro distances, we its a moderate performer. Objects are infinity are a little soft wide open but have definition and sharpens gets better as you stop down.
f/4
centre crop at infinity focus, subject at ~130m L: f/4 | R: f/5.6
As with most lenses of this period, backlit scenes reduce contrast although I don't see too many ghosts.
f/4
Servicing
The optical design is relatively simple and common for AI lenses of the period, the lens objective is in a single unit that can be removed from the lens barrel before further disassembly. The decendant f/2.8 AI-S was a lot more complicated with internal CRC mechanism but designed to keep the shorter barrel size.
(c) Nikon - Micro-Nikkor 105mm f/4 AI optical cross section
To access the lens objective, you will need to locate the grub screw hidden under the lens hood - note its note at the full extended hood position so you will need to patient. Once located, loosen the grub screw and unscrew the hood.
The rear block is accessed by removing the rear baffle but this is secured via lacqure so you will need to run a line of acetone into the hole and wait. The rear baffle also secures a mechanism to move the iris - a pin exists in the block so you must be careful to align when reassembling. The rear element can be freed with a lens spanner once the baffle is removed. The front block requires unscrewing the front via a rubber cone tool to have access - once the front block is removed you will have access to the aperture blades so need to be careful.
Re-installing the objective needs care and better with the bayonet removed so you can clearly see the alignment of various peices: the iris actuation "foot" and the stop down lever. With the optical block inserted, you can align the bayonet mount stop down lever/fork with the "pin" of the iris actuation foot.
L: long rod is the iris actuation lever | R: note the outward position of the "foot" that actuation lever sits
Top: pin required to align with the bayonet's stop down lever/fork - the pin MUST be positioned perpendicular to accept the stop down lever/fork
Optics
The lens has a 5 element / 3 group design and the lens objective lifts out in one peice. You will discover that there is a notch out of the objective (its not sealed!!) that will allow dirt/dust/moisture inside the optics either side of the aperture blades.
The objective can be pulled from the front of the barel once the hood/retaining collar are removed.
Notice the notch/slot that gives free roam for extra dirt to get onto the lens elements - this is notched out to allow the aperture activation level to pull the foot (sitting just outside the notch) into that space.
Acetone the seal and twist off the rear baffle and then lift the aperture lever.
At this point you can use lens spanner to free the rear element - it was really tight on mine and I didn't need to get full access to the rear element so left it untouched. You can use qtips/cotton swabs much more easily to clean the rear element here.
Notice that the aperture lever that was removed has a fork that has to sit on this pin in the objective's groove when reassmebling. You know you got this correct as moving the aperture lever will fully open or close the iris.
From the front unscrew the block that contains the front 3x elements - you can do this the first time as the front baffle is laquer sealed.
observe the notch in the lens objective for the aperture activation foot
Apply acetone to the front baffle and rear (gold) collars and twist off to get accses to the elements.
Helicoids
Accessing the helicoids requires you to fully dismantle the rest of the lens - as Richard Haw notes in his article the screws securing the helicoid key are increbidly difficult to remove: I was unable to free those screws even with soldering iron/IPA/acetone/lighter fluid.- Lift name plate after removing the 3x screws - this will expose screws securing the focus ring
- Remove the 3x screws from focus ring and lift
- This silver key limits rotation (note the notch on the exposed helicoid. You will need to remove this key to seperate the helicoids.
- Remove the 3x screws on the chrome grab ring - mark the focus position to have a reference point before removing the sleave to reveal the helicoid screws.
- This is where I get stuck - these screws would not budge no matter what I tried. If you get here and you can remove the helicoid key you will be able to seperate the helicoids for cleaning.
Given this copy was suffering from gritty/sticky focus - and the inability to remove the helicoid keys - I took a less than optimal approach; from the rear of the extended lens it is possible to somewhat get access to some parts of the helcoids and similarly when the focus ring is removed. With this limited access I was able to flood/clean the exposed parts of the helicoids with lighter fluid and then 99% IPA using a small headed toothbrush - with constant extend/collapse of the focusing helicoid I was able to flush a lot of old grease and more importantly gritty/dried lumps of grease. When it felt that there were very limited grease left - the extend/collapse feeling very light and dry - I applied a very thin layer of new (Japan Hobby Tool #10) grease using the same exposed helicoids and this seemed to help. Not perfect but effective (so far) with no apparent binding/clumping with the old grease.
view of helicoids from rear
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