Nikon Nikkor UD 20mm f/3.5

Nikon Nikkor UD 20mm f/3.5

Introduction

Nikon Nikkor UD 20mm f/3.5 was the first retrofocus type 20mm prime for Nikon's now ubiquitous F mount series of cameras. The lens replaced the original Nikkor-O 21mm f/4 rangefinder prime (which users could still use on SLR cameras with mirror lockup - somewhat of a hassle in its own right). The lens was produced from 1967 throug 1974 and was eventually succeeded by a slightly slower, but more compact 20mm prime. The Nikkor UD 20mm f/3.5 is a non Ai lens and does not offer automatic indexing. This also means that the lens cannot be mounted on many of newer bodies without modification - the metal metering prong has to either be removed or shimmed sufficiently so it does not hit the body prism during mounting. The Nikkor UD 20mm is commonly available on used markets and typically sells for ~US$200 (as of March 2009).

The optical construction of the lens consists of 11 elements in 9 groups. The lens carries an UD designation, but this does not really mean that the lens incorporates a UD element. Nikon used  letter codes in 60s to designate the number of elements in the lens design, and UD actually means  Unis +Deci, or 11 elements (thanks Roland for clarification). The build quality of the lens is superb, as is the case for majority of older Nikon lenses - the barrel is metal as are the aperture and focusing rings. The focusing ring is pretty smooth and the aperture ring is snappy, moving in one full f-stop increments. The minimum aperture setting is f/22.  The lens is slightly larger then the new versions of Nikkor 20mm, measuring 75 x 70mm (2.9 x 2.7in) and weighing 390g (13.8oz). The minimum focusing distance is 30cm (1ft) and the lens accepts 72mm screw-in filters.

The lens can in theory be adapted to alternative mount cameras. There are some caveats through. The lens can be used (with an appropriate adapter obviously) on any Four Thirds camera, as well as APS-C type Canon bodies. However, you should be extra careful when trying to use this lens on any full frame Canon bodies since the protruding fin on the back of the lens can hit the mirror box of the camera. You should really consider cutting or shaving it off if you plan to use the lens on a Canon FF body - the operation of the lens will not be affected and you would still be able to use the lens on Nikon bodies (assumiing of course you also converted it to Ai).

 

Summary
Lens Composition 11 elements in 9 groups
Angular Field 94 degrees
Minimum Focus 30cm/1ft
Focusing Action MF
f-stop Scale f/3.5-f/22, manual
Filter Size 72mm
Lens Hood Metal screw-in (included)
Weight 390g/13.8oz
Dimensions 75x70mm/2.9x2.7"
Lens Case No. 5 (included)

 


 

Field Tests

If you are into landscape photography, then you are probably like  me - always in search for a better wide angle. Well, for different people the definition of 'better' will be different of course, but the usual rule(s) of thumb apply here - sharp, contrasty, good color rendition. What else? For me, it's also reasonable price. There are quite a few really excellent ultra-wide angle lenses out there that cost an arm and a leg and then some more., but quite few at reasonable price. And Nikkor UD 20mm f/3.5 certainly falls into this category. For ~US$200 you can buy a sample in a pretty decent condition. That, plus often gang-ho comments about this lens from online users made me curious to give it a try.

As mentioned earlier, Nikkor UD 20mm f/3.5 was designed for the Nikon F series and is a non Ai lens, meaning that it requires conversion and remachining of the aperture ring if you want to use this lens on modern Nikons. Once converted to Ai, the lens will still retain automatic diaphragm control, and if your camera supports non CPU lens data input as well as  metering with manual lenses, then you will also be able to retain full EXIF information when shooting the UD Nikkor. Other then the need to  convert the lens to Ai, the lens will work like any other fully manual lens.

If you are using a manual lens on a modern digital body, it is likely that you are using a stock focusing  screen, which regretfully is not well suited for accurate manual focusing. With long lenses you can rely on your eyesight when trying to focus, but with ultra wide angles manual focusing without visual aids like split circle screen is going to be pretty tough, simply because of the enormous DOF delivered by wide angles Some cameras like D3 have digital rangefinder, which can certainly be quite helpful but is still not going to be as accurate as a split circle. Now, I have to disclose that I personally don't use a split screen on my Nikons, but when I shoot landscapes, my typical aperture settings are f/8 and f/11. At f/11, the Nikkor UD 20mm f/3.5 will give you a focusing range from about 1.5m to the infinity if you use hyperfocal focusing (note that the UD Nikkor does not have a real DOF scale on the barrel, but there are marks on the chrome ring that can help you simulate the DOF scale). Plenty of focusing coverage for me and probably fo most users. Also, considering that the maximum aperture of the lens if pretty slow to begin with, you are not going to be able to achieve shallow DOF even with wide open aperture and at the minimum focusing distance. Take a look at the shot below, where the central portion of the chain link was placed into focus at ~35cm. You get some separation with out of focus background and foreground blurred slightly due to the slightly shallower DOF, but nothing particularly special.

 

ISO 200, 1/2000, f/3.5, 20mm (Nikon D3)

 

Image resolution with Nikkor UD 20mm f/3.5 was not particularly impressive, as the lens showed quite noticeable amount of softness on both full frame as well as APS-C bodies around borders.  Now, soft corners and wide angle lenses go hand-in-hand  with each other (pardon the pun), in many cases simply because the wide angle lens designs can't achieve a truly flat field curvature, and there is a minor difference in distance across the frame between the focusing plane and the subject. In other cases, distortion, which is quite typical to wide angles, creates an impression of softer corners. Either way, you will notice that if you want to achieve some uniformity across the frame, you'd need to shoot at f/8 and beyond. Even then, border image quality would remain slightly softer when compared to image center, which by the  way is excellent throughout the aperture range.

And speaking of the distortion. The UD Nikkor is surprisingly well corrected for distortion, which is a no small feat for such a wide lens. If you take a look at the images in the sample gallery, you will notice that streight lines even around extreme edges show pretty minimal curving! Kudos to Nikon here...

Like with most ultra wide angle lenses, you should be careful about composing your pictures with UD Nikkor 20mm f/3.5 when a strong light source, like the sun, is positioned within or close to the picture frame. In the shots below, with the sun rays hitting the front element of the lens at ~60 degrees, you can see that the lens falls prone to pretty pronounced flare pretty much throughout the entire aperture range. Aperture ghosting, reduced contrast, glare, de-saturation, color streaks, you name it and  it's going to be present. The lens is a giant light sink, so be careful there.

 

ISO 200, 1/500, f/3.5, 20mm (Nikon D3)
ISO 200, 1/125, f/8, 20mm (Nikon D3)

 

And like with most wide angles, Nikkor UD 20mm f/3.5 showed pretty noticeable vignetting, particularly on a full frmae camera. Even with such a slow maximum aperture, the light falloff noticeably darkens the corners of the picture frame, so if your camera has a built-in vignetting control, you might want to set it to medium to get rid of this artifact. Vignetting actually remains visible until f/5.6. On an APS-C body, light falloff is noticeable as well, but not to the same extent as on a FF body. You still need to stop down to f/5.6 to completely get rid of it though.

 

Vignetting @ 20mm - full frame vs APS-C

 

The biggest surprise for me personally though was the color rendition of this lens. Now, many lenses can produce corner to corner sharp images, and in my book, resolution is one of the few most important factors when choosing a lens (it might not be for you though). But resolution alone is often not sufficient: you would also want a lens that is capable of reproducing colors as accurately as possible and preserving infinitely small tonal transitions. For portrait type lenses, quality of bokeh is another potential factor to be considered. Since we are dealing with an ultra wide angle lens here, bokeh is the least thing one would care about, and considering that most landscape photography will be shot at smaller apertures, the issue of soft borders is going to be mitigated as well. So what is left? Yep, color and contrast. And this is where the lens delivered a pleasant surprise. The lens seems to be capable of accentuating warmer tones, giving colors a boost in saturation and adding a touch of yellowish glow. All while still preserving pretty decent contrast in midtones. Other, typically older, lenses are also known to create yellowish casts - many speculate that this is because manufacturers used to add some radioactive materials to the lens caoting material. I can't really confirm whether this is the case  with Nikkor UD 20mm f/3.5, but the look and feel of the color palette was quite pleasant. It is also worth mentioning that unlike some of Canon's lenses, which often also generate warmer palette, Nikkor did not seem to overblow reds, but obviously with the slight boost in yellow color, your pure reds will no longer be pure. Obviously, not everyone will find this desirable in a lens, but can you think of situations where this characteristic can be of use? I can - sandy beaches, sunsets, you know that magical moments when everything around you starts glowing and turns golden. Ok, the final note on color reproduction is color fringing. You can actually notice some lateral color aberration in images once you blow them to 100%. Particularly around high-contrast transitions - take a look at a couple of the street shots in the image galler and notice pinkish edges around leaves and restaurant/shop signs.

 

ISO 200, 1/3200, f/3.5, 20mm (Nikon D3)

 

 


Lab Tests

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

 

Resolution: Nikon FF

As noted in other reviews, it is really hard to design an ultra wide angle lens with consistent resolution across the entire frame. This was tru backin 60s and 70s when the first 20mm Nikkors were born and this remains true even today, when more advanced manufacturing technologies have become available. Hence the expectations for Nikkor UD 20mm f/3.5 have always been rather muted. So when the lens turned mixed performance in the lab, there was no big disappointment to begin with. Still, for a 30 year old. Nikkor managed to squeeze very good center image performance throughout the tested aperture range. Very consistent results here. Borders  did suffer though, particularly with wider apertures. You really need to stop down the lens to f/8 to see more consistent across the frame results. Conclusion? It is hard to expect a miracle from a 30 year old lens, so I guess there is no disappointment. But there is no excitement about it either. Stop down to f/8-f/11 if you care about sharpness.

Normalized raw MTF50 @ 20mm

Resolution: Canon APS-C

With smaller sensor and therefore smaller circle coverage, one usually homes that APS-C cameras would be a little bit more forgiving towards the wide angle lenses and their almost inherent weakness in border performance. In the case of Nikkor UD 20mm f/3.5, the smaller imaging circle coverage helped only so much - border image quality still suffers quite noticeably at f/3.5 and f/4. Even at f/5.6 performance is only average and you do need to stop the lens to f/8 or f/11 to achieve best results. Well, at least center image performance is consistent. The peak is in the f/8-f/11 range,  where the lens  can give you excellent 11in and decent 19in prints. Conclusion? Consistent results both FF and APS-C bodies, albeit consistently mediocre border performance at f/3.5 through f/5.6 is not that welcome.

 

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

 

 

Normalized raw MTF50 @ 20mm

Normalized raw MTF50 @ 20mm

 

Chromatic Aberration: Nikon FF

Chromatic aberration on a ful frame Nikon was quite modest, for a wide angle that is. CA in the center  was minimal throughout the tested aperture range, never exceeding ~0.3px, while CA around borders hovered at ~1px throughout the most of the aperture. Not that bad.

Chromatic Aberration (Nikon FF) @ 20mm

Chromatic Aberration: Canon APS-C

CA on an APS-C body was ever slightly higher then on a FF camera. Center CA still remained quite under control, going from ~0.4px at f/3.5 to ~0.2px by f/11. Border CA did go up slightly - at f/3.5 CA reached ~1.1px, but slowly dropped to ~0.9px by f/11. Still not the worst  possible results  for an ultra wide angle lens.

Chromatic Aberration (Canon APS-C) @ 20mm

 

Vignetting

The lens showed pretty noticeable amount of vignetting on a full frame body - at ~1.8EV, the picture frame corners will be noticeably darker at f/3.5, so you might want to turn on your in-camera vignetting control. On an APS-C body the light faloff is significantly less, thanks to the smaller coverage the APS-C sensor provides, but even then, at ~1EV youwould notice a little bit of vignetting here as well. Stopping down to f/5.6 and beyond would minimize the amount of vignetting on both FF as well as APS-C bodies.

Vignetting on APS-C and FF cameras

 

Distortion

Barrel distortion is a common domain of ultra wide angle lenses, and this is where Nikkor UD 20mm f/3.5 delivers the biggest surprise! At ~0.95%, barrel distortion is minimal for such a wide angle!. Such low distortion in a 20mm is practically 'unheard of'.

 

Distortion @ 20mm

 

Chart Crops: Nikon FF

Here are 100% crops, taken with a FF Nikon D3, comparing image borders at f/3.5 and f/8.

Image borders @ 20mm - f/3.5 vs f/8

Chart Crops: Canon APS-C

Here are 100% crops, taken with an APS-C type Canon Digital Rebel XTi, comparing image borders at f/3.5 and f/8.

Image borders (Canon APS-C) @ 20mm - f/3.5 vs f/8

 

 


 

Alternatives

Nikon has been continuously manufacturing 20mm wide angle lenses since the introduction of the rangefinder Nikkor-O 21mm f/4, so it would probably make sense for you to start your search for alternatives among the various 20mm Nikon primes, including Nikon Nikkor 20mm f/4 Ai, Nikon Nikkor 20mm f/2.8 AiS and Nikon AF Nikkor 20mm f/2.8D. Nikon users (as well as those willing to adapt alternative lenses) might want to consider the recently released Voigtlander Color Skopar 20mm f/3.5 SL II (also available in Pentax K mount). If you are exclusively looking for an alternative wide angle prime, you should consider the duo of Zuiko OM 21mm lenses Olympus OM 21mm f/2 and Olympus OM 21mm f/3.5. Leica affectianados should consider Leica Elmarit-R 19mm f/2.8, while Carl Zeiss fans would swear that Contax branded Carl Zeiss Distagon T* 21mm f/2.8 is the best wide angle prime ever manufactured. Speaking of the Distagon T* 21mm f/2.8 - Carl Zeiss recently re-released its SLR series of lenses, which also includes the new version of Distagon T* 21mm f/2.8 in Nikon F (ZF), Pentax K (ZK) and even Canon EF (ZE) mounts.

 

Recommendation

Nikon Nikkor UD 20mm f/3.5 can be quite an interesting lens to explore, if you're into manual focus lenses of course. The lens is by far not without drawbacks, so you should not expect miracles from it. But if you are willing to adjust your expectations, Nikkor UD 20mm f/3.5 can become an enjoyable lens to use. Among the most interesting characteristics are the fenominally low (for an ultra wide angle lens) distortion and rich, super-saturated colors and good contrast reproduction (at smaller apertures at least). Among things to consider is the rather low resolving capabilities around borders and obviously vignetting and flare. But the most enticing factor to many would be the price - a 20mm prime for less then US$200? Considering that the demand for these old lenses remains quite steady, trying it poses very little risk - you will always be able to sell it back at any time.