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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