Nikon 20mm f/1.8G Lens Review

bythom 20mm-G-series.jpg

From left to right: 20mm, 24mm, 28mm, 35mm, 50mm, 85mm f/1.8G


What is It?

The 20mm f/1.8G is one in a continuing series of Nikon’s redesigned primes. We now have 20mm, 24mm, 28mm, 35mm, 50mm, and 85mm f/1.8 lenses, with very similar feature sets and all designed using Nikon’s newer approach to lenses.

Aside. One thing is clear from this series, someone at Nikon didn’t get the message about video in DSLRs. We don’t have an aperture ring or E-type electronic aperture functions, nor do we have focusing that is well suited to video. Sad. 

bythom nikon 20mm.jpg

Primes don’t tend to be complicated lenses. The pertinent things you’ll want to know about the lens being reviewed are:

  • Maximum f/1.8 aperture, minimum f/16, with a 7-blade aperture diaphragm
  • Minimum focus of about 8” (0.20m) with a 1:4.3 maximum magnification
  • 12.5 ounches (355g) and only about 3.2” long (81.3mm)
  • 13 elements in 11 groups, with 2 aspherical elements, 2 ED elements,  and Nano coating
  • AF-S focus (works with all Nikon DSLRs, even those without in-camera focus motors)
  • No VR, no tripod mount, simple MA/M switch
  • 77mm filter ring
  • The HB-72 lens hood and CL-0915 soft pouch come with the lens

There’s a wide focus ring and a minimal depth of field scale (markings for f/16 only). 

Nikon’s page for the lens is here. The lens is made in China and retails for US$800. 

Source of the review sample: personal purchase. Results compared to one other sample lens available to me.


How’s it Handle?

This lens is probably a bit bigger than you’d expect for a 20mm f/1.8, but since you’re almost certainly using it on an FX body (not a terribly useful focal length for DX, though it can sub in as a 30mm wide angle prime for DX), that’s not going to probably be an issue. The lens feels a bit more dense than the 28mm (similar size, heavier weight), but it’s not exactly a burden to carry at 12.5 ounces. 

The focus ring on the lens rotates one-quarter turn from minimum to infinity focus. On my sample the ring feels somewhat tight and reasonably precise. Even so, there’s not enough discretion or directness for extremely fine tune focus precision. Note my comment about video, above. Also focusing isn’t exactly silent, either, though my 20mm sample is far quieter than my 28mm, and less rough than my 24mm. 

One peeve with all the f/1.8 lenses I have that relates to handling is the differing filter size: 77, 72, 67, 58, 58, and 67 for the 20mm, 24mm, 28mm, 35mm, 50mm, and 85mm respectively. This means you need probably at least three sets of filters, maybe four (I’d probably handle the 72 and 77 requirements with a 77mm filter and 72-77mm step-up ring.)


How’s it Perform?

Focus: As with all the f/1.8G primes, focus performance isn’t what anyone would call snappy. The 20mm, however, is one of the faster of the f/1.8 lenses in autofocus acquisition, probably because it’s not moving much mass during focusing. 

Sharpness: Nikon’s new lens design system seems to produce lenses that are consistently very good to excellent in terms of acuity. While we don’t get the exceptional results you see with, say, the Zeiss Otus lenses, recent Nikkor primes have been well-behaved and well balanced. 

The sharpness measurements here bear that out with a bit of an exception: there’s literally nothing exceptional to write about (but also nothing problematic to write about). For FX, the best aperture is probably f/5.6, though f/4 is also very close. Center performance is excellent across the board, but at f/1.8 in the corners you’re going to find a large degree of blur, some of which seems to be due to field curvature. By f/2.8 the corners are very good, maybe even excellent, though they’ll improve at smaller apertures. Still, watch out for field curvature on flat fields.

On a D8xx model, diffraction starts robbing back a bit of that excellence at each aperture above f/5.6, but that still leaves the lens doing quite well at f/11. I wouldn’t avoid the smaller apertures. 

Curiously, on DX things are a little different. Enough so that you wonder if Nikon was designing with DX in mind on this lens. I mentioned the corners being problematic wide open on FX. Not really so on DX, even though my sample was slightly miscentered. Wide open on DX is as good as f/2.8 on FX with this lens (in other words, very good corner to corner, probably excellent in the middle). When you stop down to f/2.8 in DX, the corners don’t get better (still very good) but the center does. You absolutely need to get to f/5.6 to see optimal edge to edge performance in DX, and at that point it’s not just excellent, it’s nearing exceptional.

Chromatic Aberration: lateral CA is certainly present, but it’s very consistent just above the one pixel mark (on a D810) at every aperture. Easily corrected, and is corrected by most recent Nikon bodies shooting JPEG. Longitudinal CA is present, with green shift beyond the focus point and magenta forward. By f/4 this is minimized, but it’s present to a small degree at every aperture. This is fairly typical for fast prime lenses, actually, but it can be problematic in some photographic situations and is difficult to remove.

Vignetting: Probably the worst characteristic of the lens. It vignettes in FX substantially at f/1.8 (more than 1 stop). By f/2.8 the vignetting is mostly ignorable, and certainly by f/4 it is ignorable. Again, many modern Nikon’s have the ability to correct for this in JPEGs. 

Linear Distortion: Very good, actually. Under one percent barrel distortion, and it appears that this is free of complexity, so again, easily corrected should it prove something you feel you need to fix.

Bokeh: I’d characterize the bokeh, even wide open, as slightly busy. The Latitudinal CA is part of the culprit. Unlike my other f/1.8 Nikkors, my 20mm sample was nearly perfect symmetrically in the aperture blades, which makes the stopped down bokeh pretty decent. Nothing to write home about, but nothing unpleasurable, either.


Final Words

The 20mm is indeed finding a place in my bag much of the time. It turns out to be a fairly decent landscape lens, with no flaws that bother me and plenty of acuity for the D810. It’s also somewhat useful as a 30mm equivalent on my DX bodies, and there it makes a very nice companion to the 35mm f/1.8G DX lens, though probably in a bigger package than you’d like for DX.

Of the f/1.8 prime series so far, this 20mm, the 24mm, and the 85mm are my favorites, by far. Very well behaved, good acuity even wide open, and just fast enough over the f/2.8 zooms that they find uses. 

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