Nikon AF-S Nikkor 20mm f/1.8G ED review – Image quality
For landscape images, the 20mm f/1.8 lens delivers on its promise. There is very little curvilinear distortion, which is evidenced when selecting the automatic profile correction in Adobe Camera Raw or Lightroom. A press of the button makes a slight adjustment to the image, but it isn’t severe at all. Those wishing to shoot architecture or interiors should also find the minimum distortion a real benefit.
Vignetting is present, as you would expect from a lens of this focal length, and can be noticeable even at f/8. Vignetting bothers some people, but I’m not one of them – it helps draw the eye to the centre of the frame, and it can be easily removed when editing.
In terms of sharpness, the corners do suffer when shooting wide open. However, by f/5.6 they are much sharper, and at f/8 it is only the very corners that have a noticeable drop in resolution from the centre of the frame.
Shooting right into the sun, some green/magenta chromatic aberration was noticeable. However, this was a very extreme test that I would have expected almost all lenses to fail. Even with the slight aberration, the 20mm coped admirably with the ordeal, and again, the benefit of modern technology meant the raw file was corrected with the press of a button, leaving no trace of it at all.
When using the 20mm lens on a DSLR with an APS-C-sized sensor it becomes the equivalent of a 30mm f/1.8, and it uses the very sharpest part of the imaging circle. Used in this way it will give you virtually edge-to-edge sharpness that is every bit as good as the very centre of the frame. Again, this is something that will appeal greatly to landscape photographers.
However, the aspect I most enjoyed was the f/1.8 aperture. Focusing on subjects that are very close to the lens – even as close as the 20cm minimum focus distance will allow – meant that I could be very creative when framing images. It offers something different for all types of photography, but it is perhaps those shooting video who will benefit the most, creatively, from this lens.
Nikon AF-S Nikkor 20mm f/1.8G ED review – Resolution
Our MTF tests reveal fairly typical behaviour for a fast prime lens. At f/1.8 the centre of the frame is quite sharp, but the edges are noticeably soft. Stop down to the lens’s optimum aperture of around f/5.6 to f/8, though, and the lens performs very well. Smaller apertures will result in diffraction blurring.
Nikon AF-S Nikkor 20mm f/1.8G ED review – Shading
As usual for a fast prime lens, shading is quite pronounced at maximum aperture, but our graph reveals a gradual fall-off profile across the frame that’s unlikely to be visually objectionable in most circumstances. Stopping down reduces the effect considerably, with only very low levels of vignetting at apertures of f/4 or smaller.
Nikon AF-S Nikkor 20mm f/1.8G ED review – Curvilinear distortion
One big advantage of prime lenses over zooms tends to be better control over distortion, and that’s evident with the 20mm Nikkor. A figure of -1.2% is indicative of mild barrel distortion. In many situations this won’t be noticeable, but it can be easily corrected in post-processing for more critical subjects such as architecture.