AF Micro Nikkor 105 mm f/2.8
Since 1974, Nikon produced several versions of a 105 mm macro lens in Nikon F mount. The first version was a 105 mm f/4 with manual focus up to 0.5x in black metal barrel. Its mechanics were upgraded a few times, then replaced by a 105 mm f/2.8 in metal barrel, also with manual focus up to 0.5x. The latest version of this lens appears to be still available from Nikon.
The subject of this page is the AF Micro Nikkor 105 mm f/2.8, introduced in 1983, and replaced in 2007 by a redesigned version with internal focus and image stabilization (called VR by Nikon). This lens is designed for film SLRs, and therefore covers full-frame as well as APS-C sensors.
The AF Micro Nikkor 105 mm f/2.8 seems to be the first Nikon macro lens of this focal length to reach 1x without extension tubes. It is mounted in a mixed plastic and metal barrel, and the front of this barrel extends (without rotating) by up to 28 mm when focusing. The main optical assembly is located deep within this front barrel when focused at infinity, and slides all the way forward by another 22 mm when focused at 1x. A second optical group behind the first one slides forward and back when focusing, and a third group is fixed near the rear lens mount. The optical scheme uses in total 9 elements in 8 groups, which is within the normal range for a modern macro lens. The effective focal length reduces to about 78 mm when the lens is focused at 1x. The working distance at 1x is 133 mm.
Autofocus is driven by a mechanical connection to a motor in the camera body. Only cameras with this mechanical coupling can autofocus with this lens.
This lens has a few mechanical controls only present on Nikon lenses of roughly the same period, which must be understood if the lens is used on a third-party camera (e.g., a mirrorless camera via a lens adapter).
A plastic ring immediately at the rear of the focus ring switches between autofocus (A) and manual focus (M).
A small round metal button on this ring must be kept pressed when rotating the ring. The button acts as a safe to prevent accidental switching between manual focus and autofocus. This plastic ring has a known tendency to crack around its metal button. If the lens is dropped, the plastic ring may also crack at other points along its circumference. It is a good idea to check the integrity of the ring when inspecting a second-hand lens. Only manual focus is possible when this lens is used on a third-party camera, or a Nikon camera without AF motor. Therefore, the ring should be left in the M position in this case. Setting it to A disengages the focus ring and makes manual focusing impossible.
A focus limiter switch mechanically restricts the focus distance between infinity and 47 cm (about 0.33x), or between 43 cm (0.4x) and 31.4 cm (1x). The focus limiter has no practical usefulness when manually focusing, so it should be left in the FULL position.
A small plastic switch at the fore of the aperture ring is used to lock the latter at f/32, enabling automatic aperture control and stopping down by the camera via a mechanical lever. When the lens is used on a third-party camera, this switch must be kept disengaged (i.e. pushed forward) to allow manual aperture control. The f/32 setting on the aperture ring is printed in orange, to remind the user that this aperture must be set before the aperture lock switch can be engaged.
The aperture ring has a double aperture scale. The rearmost of these scales was visible through a periscope in the pentaprism viewfinder of certain Nikon SLRs. It has no use on Nikon DSLRs or third-party cameras.
A 52 mm filter mount is present at the front end of the lens barrel that extends while focusing. This barrel is surrounded by a 62 mm thread at the front of the fixed portion of the lens barrel. Naturally, neither filters nor lens caps can be mounted on this thread. I believe the 62 mm thread is meant for attaching a lens shade. Once attached here, the lens shade does not extend when the lens is focused into the close-up and macro range, and therefore does not reduce the working distance, and does not significantly block light sources (e.g. electronic flash) placed around the lens barrel. Alternatively, the 62 mm thread could be used for attaching a macro flash to the lens without placing a mechanical stress on the extending barrel and the focusing helicoid.
The next question is which lens shade can be used for this purpose. The legacy Nikon HN-24 lens shade is recommended for a few zooms of focal lengths that start at 70 to 100 mm, so it would seem reasonable for use on the AF Micro Nikkor 105 mm. This lens shade does look a little too short and too wide on the AF Micro Nikkor 105 mm, but one must consider that the front element is deeply recessed when the lens is focused at infinity. The HN-24 may block light sources placed closely around the barrel, but this is not likely to be a significant problem at magnifications up to about 0.5x. It does not reduce the working distance of the lens at 1x, but between 0.5x and 1x it is better to remove the lens shade unless sunlight directly hits the front element of the lens.
It is also worth pointing out that the front lens barrel and recessed front element, in themselves, effectively combine to work as a lens shade at magnifications up to about 0.5x, making an added lens shade not required in most cases. Nonetheless, it is good to know that the HN-24 can be used on full frame in extreme cases. A narrower lens shade can be used with this lens on APS-C or Micro 4/3.
The Nikon HB-38 lens shade is recommended for the internal-focus version of the Micro-Nikkor 105 mm, mounts on the front bayonet of this lens, and does reduce its working distance, as well as does block light sources placed around the barrel in the close-up and macro ranges.
Figure 8 also shows the lens mounted on a Metabones Nikon F to Micro 4/3 adapter. This adapter has a small but solid Arca-compatible plate that is useful to attach the lens (as opposed to the camera body) to a tripod head. Doing this prevents a mechanical loading of the camera body and lens mount.
The above figure is a close-up subject (top) and two 1:1 center crops of the same a 42 Mpixel image shot with this lens at 0.45x and f/8. The aperture was chosen as a compromise between relatively high DOF and low diffraction. There is virtually no blurring, and plenty of detail in a size range of a couple of pixels. Focus was relatively difficult to nail down with precision, even using the highest live view magnification available on this camera. Note that the subject is highly convex, and therefore only parts of the center crops are in perfect focus.
One additional problem is that rotation of the focus ring is not very smooth and has a plastic-on-plastic feel in my specimen of the lens. Focusing with a micrometric linear stage would be far easier.
The AF Micro Nikkor 105 mm f/2.8 is a good legacy macro lens reaching 1x without extension tubes. Focusing with floating optical groups provides a reasonable compromise among lens size and weight, image quality, ease of operation and reasonable price. In spite of the optics having been designed in the 1980s, this lens remains a reliable choice today.