5) Lens Sharpness, Contrast and Color Rendition
When I initially saw the manufacturer-provided MTF curve of the Nikkor 20mm f/1.8G ED lens, I got very excited to see how good it looked when compared to the 28mm f/1.8G lens. Both sharpness and contrast of the lens looked very promising at maximum aperture, so I imagined how good the lens would get when stopped down. When I finally measured the lens in my Imatest lab, my early estimates proved to be correct – the lens does indeed perform extremely well for a wide angle lens. Not only did it outperform the 28mm f/1.8G lens, but it also yielded better sharpness figures in the center than the legendary 24mm f/1.4G lens! Take a look at the below chart:
The Nikkor 20mm f/1.8G ED starts out very strong at large apertures. Center performance is excellent wide open, with performance characteristics being very similar to those of the Nikkor 35mm f/1.8G ED lens. At f/2.8, the lens yields very impressive sharpness in the center, which only slightly improves when stopped down. Peak center performance is reached at f/4, with excellent overall performance at f/5.6, where both mid-frames and corners look very good. Unlike the 28mm f/1.8G lens, the 20mm f/1.8G practically had no focus shift and field curvature was far better controlled too. To see how good the above lens compares to other Nikkor primes like 24mm f/1.4G and 28mm f/1.8G, please see the comparisons section further down below.
Thanks to the excellent optical design of the lens, microcontrast is also superb, very similar to what you see on very expensive and high-end Nikkor lenses. Thanks to Nano-coating, Super Integrated Coating and high quality glass used in the lens, the Nikkor 20mm f/1.8G ED yields very natural and pleasing colors.
Wide angle lenses are not suited for yielding pleasing bokeh and the Nikkor 20mm f/1.8G ED is not an exception. As I have previously demonstrated in a number of reviews, use of aspherical elements usually results in onion-shaped bokeh, so if you look really close at how the lens renders bright out of focus highlights, you will definitely see those onion rings. At the same time, out of focus transitions look rather pleasing and not as distracting as they typically do on zoom and lower-end prime lenses, even when stopped down, as shown in the below image samples:
It is important to understand that with such a wide angle lens that reaches infinity at just a little over a meter, one would have to stand very close to a subject to be able to effectively isolate them from the background. And as you might already know, getting too close to your subject will distort their features, so it is best to avoid photographing people at very close distances with this lens. Although I have provided a number of examples of people photography with the Nikkor 20mm f/1.8G, the ones that show subjects close-up are cropped and others clearly show distorted facial and body features. Unless your purpose is to specifically distort the subject, make sure to keep a safe distance and avoid placing the subject in the corner of the frame.
Ultra wide angle lenses like the 20mm f/1.8G are particularly attractive to architecture and landscape photographers, who genuinely care about how such lenses handle vignetting, especially when coupled with filters. To give a good understanding of vignetting performance, I measured the lens with and without filters, at both close distance and infinity (since vignetting performance can vary greatly at different distances) and I came to conclusion that the Nikon 20mm f/1.8G performs very well with either slim or standard-size filters. Below are the vignetting levels measured by Imatest:
As you can see, at close / minimum focus distance, vignetting levels are quite normal for a fast prime. However, at infinity, the corners of the lens can get pretty dark, surpassing 3 EV on average, which is rather high.
If you are wondering what images will look like when stacking filters, here is what happens when you mount a polarizer and the LEE Filter Holder on top of it:
So keep this in mind when shooting in the field. If you really need to use a CPL together with a filter holder, my recommendation would be to get slim versions of both. Preferably, use a more versatile filter holder that allows mounting a larger polarizer, which will not add additional vignetting to your shots.
Here is the worst case scenario of vignetting performance at f/1.8 (at infinity mark, without filters), as illustrated by Imatest:
8) Ghosting and Flare
Like other pro-level lenses, the Nikkor 20mm f/1.8G comes with high-end Nano coating (Nikon calls it Nano Crystal Coat), which means that the lens is built to handle ghosting and flare very well. Indeed, shooting against bright sources of light has very little effect on the overall image, as demonstrated below:
At the same time, if you put a bright source of light in a wrong spot, you might end up with some surprises:
The above example is perfectly normal – even the most expensive Nikkor lenses will show ghosting and flare in such situations. So be careful when framing your shot and watch out for those undesirable effects.
Please note that using UV and other filters can potentially introduce more flares and ghosting to your images.
When it comes to distortion, the Nikkor 20mm f/1.8G ED measured about the same amount of barrel distortion as both 24mm f/1.4G ED and 28mm f/1.8G ED lenses, at roughly 1.06%. If distortion bothers you, it is really easy to fix in post-processing. The latest version of Lightroom already has a built-in lens profile for the Nikkor 20mm f/1.8G ED, so you can take care of it with a single click of your mouse.
10) Chromatic Aberration
Lateral chromatic aberration levels are pretty light, particularly at wider apertures, as seen below:
I would not worry about lateral chromatic aberrations though, since those can be easily fixed in Lightroom and Photoshop. As expected on fast aperture Nikkor prime lenses, there is a visible amount of longitudinal chromatic aberration present.
Although the Nikkor 20mm f/1.8G is a great performer for astrophotography compared to other wide angle lenses, don’t be surprised to see stars render into odd shapes at the extreme corners of the frame when shooting at f/1.8, as shown below:
The good news is, stopping down the lens will improve the situation dramatically. As shown above, by f/2.8, points of light are rendered similarly as in the center, so stopping the lens down will certainly improve the situation.
12) Infrared Performance
The Nikkor 20mm f/1.8G is a solid performer for infrared-converted cameras at large apertures. When stopped down to f/5.6 and smaller though, there is a visible hot spot in the center of the frame, as illustrated below (move the slider to see both):
Please keep in mind that the above images have been exaggerated to reveal the hot spot (I dialed -85 in Blacks in Lightroom). The effect is not extreme, but will be visible if you make contrast and black level adjustments.