Nikon AF 20 mm f/2.8

When I started to purchase lenses for my Olympus micro 4/3 cameras several years ago, I decided to preferably select lenses from the Olympus Pro series. For the first decade or so, this meant mostly f/2.8 zoom lenses when available, and a few primes like the 12 mm f/2 and 300 mm f/4 Pro when no corresponding zooms were yet available.

My choice for a super-wideangle zoom fell on the Olympus 7-14 mm f/2.8 Pro, which is an excellent lens but bulky, equipped with a bulbous front element and a built-in lens shade that requires a special front lens cap and prevents the use of filters. Largely because of its size and weight, I did not use this lens as often as I could have. On multiple intercontinental trips, instead of this lens I took a cheap, minuscule Samyang 7.5 mm f/3.5 fisheye wth manual focus and manual aperture. For this reason, I decided not to make the same mistake when choosing the first lenses to purchase for the Z8.

The main difference between the Olympus Micro 4/3 system when I chose it several years ago, and the Nikon Z system I am building now, is that legacy Olympus 4/3 lenses did not work acceptably (especially in AF) with adapters on the Olympus Micro 4/3 cameras of the time, while many legacy Nikon lenses in F mount do work well on Z cameras with a suitable Nikon adapter. Several of these legacy lenses, in fact, work almost as well as native Z lenses.

My choice for the first lens for my Z8 was a Nikon Z 24-120 mm f/4 S. To complement it at the "wide end" of focal lengths, I need an ultra-wideangle lens with a focal length sufficiently shorter than 24 mm to provide a significantly wider field of view (above figure). Nikon did make a few iterations of a 20 mm wideangle with different speeds (f/4, f/3.5, f/2.8), sufficiently small for my requirements. The legacy AF 20 mm f/2.8 is more than fast enough, quite small for a lens of these specifications, and capable of good image quality thanks to a relatively sophisticated optical scheme of 12 elements in 9 groups and a front floating optical group. A reasonable price and good availability on the second-hand market complete my requirements.

The legacy Nikkor AF 18 mm f/2.8 is also of good quality, but less so than the 20 mm, and is more likely to produce large and oddly shaped flare spots. The difference in focal length from the 20 mm, although visible in images, is not as great as the difference between 24 and 20 mm. In addition, the 18 mm is significantly larger and heavier than the 20 mm, uses larger filters, costs roughly twice as much as the 20 mm on the second-hand market, and is far more difficult to find. For these reasons, I did not consider it as an alternative to the 20 mm.

The above figure shows the AF Nikkor 20 mm f/2.8 (left) compared with an AI Nikkor 24 mm f/2.8 (center), and an FTZ II adapter (right). I already owned the 24 mm, I did not purchase it specifically for the Z8. The three items are roughly the same volume.

The 20 mm mounted on FTZ II cannot be called small in total size, but a single adapter can be used with multiple legacy lenses, most likely in my case macro lenses in F mount. Some space could be saved by doing away with the lens shade of the 20 mm, which according to some users of this lens is not necessary. In fact, the deep and wide filter mount already provides some protection from direct sunlight, and the angle of view of this lens is so wide that, even with a lens shade, it does include a large part of the sky.

As always with an ultra-wideangle, watch out for your fingers, your feet and your shadow becoming part of the landscape. Another thing to watch out for is the temptation to use a polarizer with this lens. The angle of view is so wide that blue sky areas become very dark in some parts of the frame and washed-out white in others.

Note that the AF Nikkor 20 mm f/2.8 and AI 24 mm f/2.8 do not provide AF when mounted on an FTZ or FTZ II adapter. Only manual focus is possible. It is not a problem for me, since this type of lens is rarely used in a hurry, or to follow unpredictably moving subjects.

Depth of field of the 20 mm is so large that for landscape, architecture and street photography it is practical to stop down, set a parfocal distance on the lens (also known as zone focusing), and shoot without checking the focus with the LCD screen or viewfinder. However, note that the depth-of-field marks on the barrel of the 20 mm are correct only for film. With the Z8, because of its high megapixel count, you must stop down the lens one more stop than indicated on this scale.

The AF 20 mm does communicate electronically with Z cameras via these adapters, and functions other than AF do work without manually reconfiguring the camera, including sensor-based VR. Using VR with the the AI 24 mm, instead, requires manually selecting a lens profile whenever alternating between this lens and other lenses that do not contain a CPU.

The above figure shows a 1:1 pixel crop of Figure 1 (rightmost part), near the center of the frame. Both detail and contrast look quite good to me for a 159 € lens, considering that this is a small portion (just over half a Mpixel) of the 45.7 Mpixel image. There were a few even cheaper specimens of the 20 mm available at the time, but I decided to splurge a little and get one in very good cosmetic condition (which is less likely to have been banged around or carelessly "serviced" than ones with visible wear, scratches and damaged screw heads).

Manual focusing is easy and precise on the Z8 with focus peaking, which I keep enabled by default with MF lenses. Although it would be possible to magnify the live view image to obtain a more selective focus, I did not find it necessary in practice.

The Z8 stops down this lens to the actual selected aperture (albeit not past f/5.6) during live view, metering and manual focusing (not with aperture fully open as typical of Nikon SLRs and DSLRs). If you are used to a DSLR and its view through the optical viewfinder with fully-open aperture, you may notice that the depth of field displayed in live view on the Z8 is often higher than what you might expect with a 20 mm f/2.8 lens.

Conclusions

The AF Nikkor 20 mm f/2.8 performs well as an extreme wideangle on the Nikon Z8.

This lens is commonly available on the second-hand market, and reasonably priced.

This lens cannot autofocus on the FTZ and FTZ II F-to-Z adapters. On the other hand, it is not the type of lens that I would use in a hurry or to follow an unpredictably moving subject. Parfocal focusing, a.k.a. zone focusing, without checking for focus on the LCD screen or in the viewfinder, is entirely practical with this lens because of its very high depth of field.

The depth-of-field marks on the lens barrel are not adequate for using this lens on a high-megapixel camera like the Z8. Stop down one more stop than it says on the depth-of-field marks of the distance scale (e.g., if you want parfocality between the focus ticks for f/5.6, stop down the lens to f/8 instead).

Manual focus is easy with this lens on the Z8 with focus peaking enabled.