Introduction

Nikon AF Nikkor 20mm f/2.8D is one of the older, AF wide angle lenses in Nikon's modern lens lineup. Released in 1994, the lens has not gone through any revisions so far. Up until mid 2000, the lens remained the widest, AF-type, rectlinear prime in Nikon's lineup (that title belongs to AF Nikkor 14mm f/2.8D ED these days). At ~US$500 (as of May 2008) for new copies and half that price for good quality used samples, the lens remains more or less affordable to non-pro photographers considering adding a wide angle to their setups.

The lens carries AF-D designation, which means that it does not have an internal AF motor. In order to auto-focus the lens, your camera has to be equipped with a drive screw, which locks into a dedicated slot on the base of the mount and rotates the lens to move into focus. This makes the lens incompatible with Nikon's entry level digital SLRs like D40/D40x (incompatible is probably an incorrect word here, since you can still mount the lens on D40/D40x, but you will loose AF and will need to focus manually). The lens still allows focus fine-tining after the camera's AF system finished focusing the lens - rotate the dedicated focusing ring a little bit to achieve the desired accuracy. The lens extends a little bit during focusing towards closeup, but the front element does not rotate, which allows using circular polarizers. The front filter thread has the diameter of 62mm. The minimum focusing distance is 25cm (0.85ft) where the lens gives the maximum magnification ratio of 1:8.3.

Image

The optical construction of the lens consists of 12 elements in 8 groups. Considering the relatively compact and lightweight format of the lens, it's surprising to see that Nikon managed to cram that many elements and groups into the lens. Of course, this is not the most compact 20mm lens ever made, but still, a 20mm prime with dimensions of 69 x 42.5mm (2.7 x 1.67in) and wight of 270g (9.5oz) is not going to burden you much. The build quality of the lens is pretty decent but not spectacular - barrel is made of hardened plastic. The aperture ring is also plastic, while the narrow focus ring is rubberized. The focus ring is pretty smooth. The aperture ring requires a little bit of force to move from one setting to another - not a problem for me personally, since I like when rings lock firmly into positions. However, some might dislike the feeling. The minimum supported aperture is f/22 and the aperture ring moves in one full f-stop increments. There's a knob next to the aperture ring, which allows locking the ring when it is set at f/22.

The aperture ring moves from f/2.8 to f/22 in one full f-stop increments. f/22 is marked on the barrel in different color - once the aperture ring is moved to this position, it can be locked by a small switch above the ring on the right hand side of it. This will enable camera to control the aperture settings directly, instead of requiring to manually turn the aperture ring.

The DOF scale is almost useless on this lens - there are only two marks, for f/5.6 and f/11, and the focusing distance scale does not have any markings between 2m (5ft) and infinity.

The groove in the base of the mount (right hand side) is designed to notify the camera that the aperture stop down is linear, which allows the camera to control the aperture settings electronically.

The automatic diaphragm pin on the left side of the mount allows the camera to open the diaphragm to required f-stop when the lens is switched to the automatic aperture control.

The slotted screw right above the pin is turned by the AF pin of the camera to focus the lens mechanically.

The ROM contacts on the base of the mount transfer distance information from the focal plane to the object being photographed to allow for advanced 3D Matrix Metering.


The factory box includes Nikon Nikkor AF 20mm f/2.8D lens, front and rear caps, registration card and manual. The lens accepts HB-4 dome shaped lens hood and is compatible with CL-305 lens case. Nikon AF Nikkor 20mm f/2.8D is a full frame lens, so on APS-C cameras like Nikon D200 its field of view will be similar to that of a 32mm lens on a full frame body. Like all AF-D type Nikon F mount lenses, Nikkor 20mm f/2.8D is easily adaptable to a few other camera mounts, including Canon's FF and APS-C bodies like Canon 5D and Canon Digital Rebel XTi. Within the scope of this review, I relied on generic non AF-chipped Nikon F to Canon EOS adapter when testing the lens on Canon bodies.

 

Summary
Lens Composition 12 elements in 8 groups
Angular Field ~70 degrees
Minimum Focus 25cm/0.85ft
Focusing Action AF/MF
f-stop Scale f/2.8-f/22, camera/manual
Filter Size 62mm
Lens Hood HB-4 (optional)
Weight 270g/9.5oz
Dimensions 69x42.5mm/2.7x1.67"
Lens Case CL-305 (optional)

 

Field Tests

Nikon AF Nikkor 2 0mm f/2.8D is quite an interesting lens - like all of Nikon's AF-D type lenses, it supports both auto-focusing and program mode along with fully manual operation through dedicated aperture and focus rings. This makes the lens a good candidate for adaptation - the 20mm camp is pretty scarce, so a lens that can be (relatively) easily adapted to most modern cameras, is quite welcome. Naturally, one should be comfortable handling a manual lens in the first place, since any adapted lens will loose its auto-focusing capabilities. An adapted Nikkor AF-D lens will also loose some of its more interesting advanced functionality, such as 3D Matrix Metering. All AF-D lenses have a chip embedded in the lens body, which transfers information about the distance to subject to the camera to enable more accurate matrix metering.

Compared to the modern ultra-sonic motors, the AF system of the lens is pretty noisy. This is partly obviously due to the mechanical prong coupling between the camera body and the lens itself - focusing starts with a loud click, then then equally loud 'wroom' and another click, which means the AF locked on the target. The speed of the AF was reasonably fast, but that's primarily due to the relatively short distance the ring has to travel - the ring rotates about 90 degrees when going from the infinity to the minimum focusing distance. Not much 'room' for precise focusing, but again, this is a wide angle, so precise focusing might not be as necessary - the depth of field is pretty vast and is likely going to mask minor errors in focusing.

The lens showcased rather mixed results in the field. Center image quality was pretty decent, even excellent once the lens is stopped down a little bit (f/4-f/5.6). However, border image quality suffered quite noticeably on both APS-C as well as full frame cameras. Border performance at f/2.8 was quite dismal, with corners 'remaining' quite smudged. f/4 did not seem to be any different and only around f/5.6 the lens started to deliver more or less acceptable results across the entire frame.

 

Vignetting @ f/2.8 - full frame vs 1.6x crop (20mm)
Vignetting @ f/2.8 - full frame vs 1.6x crop (20mm)

 

Like most ultra wide angles, Nikon AF Nikkor 20mm f/2.8D produced vignetting on both FF as well as APS-C cameras. The amount of vignetting is moderate, even with wide open aperture on a full frame body, which is a little bit surprising. The amount is further reduced with stopped down aperture and by f/5.6 it becomes practically non-existent on both FF and APS-C bodies. If you are using a Nikon D3 or any other camera with built-in vignetting control, the light falloff is going to be even less of a problem - just select one of the available vignetting control modes like 'moderate' when shooting with wide apertures and the camera will take care of the rest.

The lens fell prone to pretty nasty flare and aperture ghosting, both of which can be seen in the image below. In this particular case, the sun was hitting the lens under ~80 degrees from the left, top side, and produced large amounts of flare throughout the aperture range. Aperture ghosting, which can also be seen in the frame, persisted pretty much from f/4 through f/22. Beware of both, and try using lens shade to reduce the amount of stray light hitting the lens elements.

 

ISO 400, 1/60, f/11, 20mm (Nikon D3)
ISO 400, 1/60, f/11, 20mm (Nikon D3)

 

Color reproduction was quite decent, with images showing good amount of contrast, especially with smaller apertures. However, the lens fell prone to some color fringing, which was particularly noticeable around borders. The lens also showed minor degree of axial CA (halation) predominantly at wider apertures. Like most wide angles, AF Nikkor 20mm f/2.8D also exhibited pronounced distortion, which is not that surprising (for a 20mm that is).

 

 

Lab Tests

Please note that MTF50 results for APS-C and Full-Frame cameras as well as cameras from different manufacturers are not cross-comparable despite the same normalized [0:1] range used to report results for all types of cameras.

 

Nikon APS-C: Coming soon...

 

Nikon FF: Nikon AF Nikkor 20mm f/2.8D showed mixed performance in the lab when used on a native F mount full frame Nikon D3. Center performance was quite good in general, with already solid image quality at f/2.8 and even slightly improving with stopped down aperture. Unfortunately, border qualitysuffered quite noticeably, especially with wider apertures. At f/2.8 and f/4 border quality was mediocre at best. Even f/5.6 did not bring much improvement - borders here were kind of average. Quality finally reaches good levels around f/8, but this is a little bit too little and a little bit too late. Conclusion? Not what I'd normally call a good performing lens - based on the MTF results, AF Nikkor 20mm f/2.8 would fall somewhere in the second tier group. Still, it is worth keeping in mind the fact that the wider the lens, the harder it is to get good border performance out of it.

 

Normalized raw MTF50 @ 20mm
Normalized raw MTF50 @ 20mm

 

Chromatic aberration on a full frame type Nikon D3 was more or less under control. CA in the center was quite low, never exceeding ~0.3px across the tested range, while CA around borders averaged ~0.9px in the f/2.8-f/5.6 range, and dropped to ~0.7px by f/11. Not that bad for a 20mm prime.

 

Chromatic Aberration (FF) @ 20mm
Chromatic Aberration (FF) @ 20mm

 

Here are 100% crops taken with a full frame Nikon D3, comparing images at f/2.8 and f/8.

 

Image borders @ 20mm (100% crop): f/2.8 vs f/8
Image borders @ 20mm (100% crop): f/2.8 vs f/8

 

Canon APS-C: The lens showed rather average performance on a cropped sensor Canon Digital Rebel XTi. Center performance was very good throughout the aperture range, peaking around f/5.6. Unfortunately, border image quality was pretty uninspiring. Quality at f/2.8 as well as at f/4 was pretty miserable, I would even say unacceptable. By f/5.6 borders improve somewhat and reach OK levels. Still not very impressive though. f/8 and f/11 is where the lens finally shows results worth mentioning. Here the lens shows the most balanced performance across the entire frame, and is capable of producing good quality 16in prints. The lens is still capable of producing decent 19in prints in the f/5.6-f/11 range and 24in prints at f/8. Conclusion? Nothing special here. While performance in the f/8-f/11 range is quite good, its the wider range that worries - unless you're going for a softy/mushy border look or unless you're willing to crop the resulting frame to get rid of the smothered corners, quality around corners is going to disappoint you.

 

MTF50 (Line Width/Inch on the Print) @ 20mm
MTF50 (Line Width/Inch on the Print) @ 20mm

 

Normalized raw MTF50 @ 20mm
Normalized raw MTF50 @ 20mm

 

Chromatic aberration on an APS-C type Canon Digital Rebel XTi was somewhat high around borders - it reached ~1.6px at f/2.8, slowly dropping to a more manageable ~0.85px by f/11. CA in the center still remained quite low, averaging ~0.2px throughout the tested aperture range.

 

Chromatic Aberration (APS-C) @ 20mm
Chromatic Aberration (APS-C) @ 20mm

 

Here are 100% crops taken with an APS-C type Canon Digital Rebel XTi, comparing images at f/2.8 and f/8.

 

Image borders @ 20mm (100% crop): f/2.8 vs f/8
Image borders @ 20mm (100% crop): f/2.8 vs f/8

 

Canon FF: The lens did not produce miracles on full frame Caon 5D, which was already expected. Still, performance-wise, the lens shows good consistency - center image quality remained pretty good throughout the tested aperture range. And the border image quality continued to suffer at wider apertures - f/2.8 and f/4 remained as weak as ever. f/5.6 was kind of a transitioning point, where the lens finally showed acceptable quality around borders, while f/8 and f/11 were the peak in border performance. Conclusion? The verdict still remains the same - if you're expecting good border performance throughout the aperture from this lens, you will be sorely disappointed. f/2.8-f/5.6 seems to be the weak point for this prime (for borders that is).

 

Normalized raw MTF50 @ 20mm
Normalized raw MTF50 @ 20mm

 

Nikon AF Nikkor 20mm f/2.8D showed pretty pronounced degree of barrel distortion. At 1.57%, distortion will be visible in general photography and can cause some problems with architectural type sceneries (or anything with straight lines around borders).

 

Distortion (FF) @ 20mm
Distortion (FF) @ 20mm

 

Chromatic aberration on a FF type Canon 5D was pretty low in the center, averaging ~0.2px throughout the aperture range. CA around borders was slightly higher, reaching ~1px at f/2 and dropping to ~0.8px by f/11. Not the best results, but quite acceptable for such a wide angle lens.

 

Chromatic Aberration (FF) @ 20mm
Chromatic Aberration (FF) @ 20mm

 

Here are 100% crops taken with a full frame Canon 5D, comparing images at f/2.8 and f/8.

 

Image borders @ 20mm (100% crop): f/2.8 vs f/8
Image borders @ 20mm (100% crop): f/2.8 vs f/8

 

Alternatives

Nikon currently offers a number of wide angle lenses in its lineup, but there are no other 20mm lenses in it. If you are looking for a 20mm prime, you will need to look at third party manufacturers. Sigma currently offers a 20mm f/1.8 EX DG ASPH IF for several mounts, including Nikon F. The only other alternative for Nikon F mount is older, now discontinued Nikkor 20mm f/2.8 Ai-S version of the lens, which is obviously a fully manual lens. That's pretty much it. You can always go for a slightly longer focal length and here Nikon offers AF Nikkor 24mm f/2.8D, AF Nikkor 28mm f/2.8D and AF Nikkor 35mm f/2D. And there's the usual choice of discontinued Ai-S versions of these lenses, the best of which are Nikkor 35mm f/1.4 AiS and Nikkor 35mm f/1.4 AiS (the close focus version of the lens). However, if you are willing to consider manual focus lenses, then you should certainly take a look at the latest addition to Carl Zeiss SLR lense lineup - Carl Zeiss Distagon T* 25mm f/2 ZF, Carl Zeiss Distagon T* 28mm f/2 ZF and Carl Zeiss Distagon T* 35mm f/2 ZF. All three lenses are available in Nikon F, as well as Pentax K (the 25mm and 35mm ones are also available in M42 universal screw) mounts. And if you are willing to adapt a non-native lens to your camera, then Olympus OM Zuiko 21mm f/2 and Olympus OM Zuiko 21mm f/3.5 are also excellent choices (albeit both are getting harder to find these days).

Those of you using a Canon EF or EF-S cameras and considering AF Nikkor 20mm f/2.8D as an alternative lens for your camera, in addition to the above-mentioned lenses can also expand the search to include lenses from the now discontinued Contax lineup (these lenses are not adaptable to Nikon cameras due to a shorter register distance between the lens and the camera sensor). Among the Contax lenses you should certainly consider Carl Zeiss Distagon T* 21mm f/2.8 which has superb characteristics but sells at astronomical prices. Another interesting choice is Contax Carl Zeiss Distagon T* 15mm f/3.5, which is becoming a rarity these days. Finally, for a slightly longer focal length, consider Carl Zeiss Distagon T* 28mm f/2.8 prime, which probably offers the best bang for the buck. For a side by side comparison of several 19mm to 21mm lenses, take a look at the 19-21mm Challenge.

 

Recommendation

When compared to all other ultra to moderately wide angle lenses (18mm to 28mm) based on the overall performance, Nikon's AF Nikkor 20mm f/2.8 does not quite stack up. The lens shows weak border performance at wide apertures on both full frame as well as APS-C type cameras and falls prone to pretty much all possible artifacts - vignetting, distortion, flare, aperture ghosting, you name it. One positive factor going for this lens though is its good handling of color (which by itself should not be marginalized). However, if you narrow down the control group to only 20mm primes, then the lens would actually stack up reasonably well against some of its main competitors like Canon and Sigma. Still, if you're not willing to accept any compromises, then you'd better look elsewhere.