The following chart presents a comparison between basic parameters of different lenses designed for full frame mirrorless cameras with a focal length of 20 mm and aperture of f/2.0 or faster.
It's clear that reduced weight and portability are supposed to be the Sony's selling points - only the Sigma weighs less and it is slower aperture-wise. Mind you, the Sony is also much smaller than the Nikkor and the Viltrox.
In the photo below the Sony FE 20 mm f/1.8 G is positioned between the Voigtlander Apo Lanthar 2/65 and the Sigma A 105 mm f/2.8 DG DN Makro.
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The tested lens starts with a metal mount that surrounds a black 28×21 mm plastic frame with embedded contacts. A rear element, 29 mm in diameter, is partially limited by the dimensions of that frame as it is positioned right below it. The element is put very shallowly inside the mount, and it doesn't move.
The proper body of the lens starts with a black, plastic ring which diameter increases as you move further from the mount. On the ring you can find a white dot, making an alignment with a camera easier, the mount type (E-mount), the lens's logotype, its serial number along with information that it was produced in Thailand.
Then you see an aperture ring as wide as 19 mm and partially ribbed. The ring can move up the scale every 1/3 EV step in a classic way or work in a clickless mode, a feature that will make video recording users very happy.
Another immobile ring features a silver inscription 'FE 1.8/20 G'. On its right there is the Sony logotype and a CLICK ON/OFF toggle that allows you to control the aperture ring. On the left you see a G series mark, an aperture lock button and the focusing mechanism toggle (AF/MF).
Further on you find a manual focus ring, as wide as 20 mm. It is covered by ribbing that is very pleasing to the touch. The ring is a focus-by-wire construction; running through its whole distance range needs a turn by an angle of about 130-140 degrees, a value that is enough for comfortable settings.
Behind the ring there is also an immobile part of the lens made of metal with a red mark to make alignment with the hood easier and a hood mount.
The front element doesn't move, is convex in shape and 45 mm in diameter. It is surrounded by a part of the barrel with inscriptions stating the name of the lens, its minimum focusing distance, and a non-rotating filter thread, 67 mm in diameter. Taking into account the angle of view, offered by the lens, the filter seems to be of very sensible size.
When it comes to optical construction you deal here with 14 elements positioned in 12 groups. Inside you can find as many as two aspherical elements and three elements made of low dispersion ED glass. There is also a round aperture with nine diaphragm blades that can be closed down to a value of f/22 at the maximum.
Buyers get in the box with the lens: both caps, a petal-type hood, and a stylish, hard case of very good quality. Here I would like to praise Sony – they, unlike many other producers of optics, provide solid, proper cases for their lenses. Some of the rivals equip even quite expensive instruments with just canvas pouches so flimsy you can mistake them for cleaning cloths.
