Nikon 20mm f/1.8G ED AF-S Nikkor
Lab Test Results
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October 29, 2014
by Andrew Alexander
Nikon released an updated version of its 20mm prime lens in September 2014, offering a very fast ƒ/1.8 aperture -- the Nikon 20mm ƒ/1.8G ED AF-S. The new lens isn't a replacement for the 20mm ƒ/2.8D AF, which (at the time of writing) has not been discontinued. The manual focus 20mm ƒ/2.8 AIS also continues to be available.
The lens was designed to fill the FX sensor (or 35mm film) frame. When mounted on a DX body, the 20mm ƒ/1.8 provides an equivalent field of view of 30mm.
The lens takes 77mm filters, ships with the petal-shaped HB-72 hood, and is currently available for approximately $800.
The Nikon 20mm ƒ/1.8G ED AF-S is an impressively sharp prime lens, however, for maximum sharpness you'll need to stop the lens down to at least ƒ/4.
Mounted on the full-frame Nikon D800E, we're not surprised to see some significantly soft corners when shot wide open at ƒ/1.8, while the center of the image is very sharp. Stopping the lens down to ƒ/2.8 greatly improves the corners, and stopping down again to ƒ/4 provides almost tack-sharp performance across the entire frame. There aren't the same noticeable gains stopping down past ƒ/4, and diffraction limiting starts to set in at ƒ/8. Generalized softness is slightly noticeable at ƒ/11; at ƒ/16, it's quite obvious.
Mounted on the DX Nikon D7000, the lens performs exceptionally well, essentially cropping out the poor corners that we find on the D800E. We get almost tack-sharp performance out of the gate at ƒ/1.8, and by ƒ/2.8 it's exceptionally sharp, all the way through to ƒ/8.
Chromatic aberration is exceptionally well-controlled on the 20mm ƒ/1.8G. There is some evidence of longitudinal chromatic aberration, where fringes of purple are found near the plane of focus when the lens is used at wider apertures.
Mounted on the D7000, corner shading isn't really noticeable - at its worst (the ƒ/1.8 aperture setting), the extreme corners are around 1/3EV darker than the center of the frame. At any other setting, it's not noticeable.
Corner shading is a bit more prominent on the full-frame D800E. At the ƒ/1.8 aperture setting, we note corners that are a full stop darker than the center of the image. It's less prominent as you stop down -- a half-stop differential at ƒ/2.8, and a third of a stop at ƒ/4 and smaller.
The Nikon 20mm ƒ/1.8G ED AF-S is a wide-angle lens, so it's no surprise to see barrel distortion in its test results. It shows no more or less distortion than you might expect -- about +0.5% in the corners on the full-frame D800E.
The Nikon 20mm ƒ/1.8G ED AF-S uses an AF-S focusing motor, making it compatible with all modern Nikon camera bodies. Autofocus is fast, about one second to slew through infinity to closest focus, and is near silent. Autofocus results can be overridden at any time by just turning the focus ring.
The 20mm ƒ/1.8 isn't designed as a macro lens, but provides 0.23x magnification when used at its minimum close-focusing distance of just under 8 inches.
Build Quality and Handling
The Nikon 20mm ƒ/1.8G ED AF-S is just the right size for a prime lens, weighing in at 355 grams (just over 12oz). The balance feels good on both large and small camera bodies. The lens mount is metal and the 77mm filter threads are plastic.
The only switch on the lens is an autofocus / manual focus selector; other features include a windowed distance scale, with a depth-of-field marking for ƒ/16. There is no infrared index, but the lens will focus past infinity. As you would expect, attached 77mm filters will not rotate on the front element.
The inch-wide focus ring is rubber, a series of ribs running parallel to the body of the lens. A slight increase in resistance lets you know you've reached the end of the focusing distance, but the ring will continue to turn. There is no lens extension during autofocusing. The lens uses seven rounded diaphragm blades to make up the aperture, which should produce pleasing out-of-focus elements.
The HB-72 lens hood around 1 1/2 inches in depth. The hood is a bayonet-mount that reverses onto the lens for easy storage, but denies access to the focus ring in this configuration. The lens is nicely resistant to obvious flare from bright light sources such as the sun, but the hood works well to reduce generalized veiling flare.
There are some alternatives to consider in this category, unfortunately, we haven't yet tested any of them.
Nikon 20mm ƒ/2.8D AF Nikkor ~$570
The original 20mm ƒ/2.8 autofocus lens was first released in 1989 and then again in 1994 as a D-series lens, so it's been a long 20-year wait for an overhaul.
Sigma 20mm ƒ/1.8 EX DG Aspherical RF ~$550
Sigma has had its 20mm ƒ/1.8 available for several years.
Carl Zeiss 21mm ƒ/2.8 Distagon T* 2.8/21 ~$1850
If you don't need autofocus and like the bespoke design and high price tag of German lens designers, the Carl Zeiss 21mm Distagon might be for you.
The Nikon 20mm ƒ/2.8 AF-D has been waiting 20 years for a refresh; it's nice to see Nikon completing its prime lineup in the ƒ/1.8 configuration. The lens isn't exorbitantly expensive, and performs extremely well.
The VFA target should give you a good idea of sharpness in the center and corners, as well as some idea of the extent of barrel or pincushion distortion and chromatic aberration, while the Still Life subject may help in judging contrast and color. We shoot both images using the default JPEG settings and manual white balance of our test bodies, so the images should be quite consistent from lens to lens.
As appropriate, we shoot these with both full-frame and sub-frame bodies, at a range of focal lengths, and at both maximum aperture and ƒ/8. For the ''VFA'' target (the viewfinder accuracy target from Imaging Resource), we also provide sample crops from the center and upper-left corner of each shot, so you can quickly get a sense of relative sharpness, without having to download and inspect the full-res images. To avoid space limitations with the layout of our review pages, indexes to the test shots launch in separate windows.
Nikon 20mm f/1.8G ED AF-S Nikkor
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