Sigma 20mm F/1.4 DG DN | A

Sigma released this 20mm f/1.4 prime in 2022 for full-frame mirrorless cameras, and it remains in production. It comes in Leica L and Sony E mounts, and the A in the name stands for Art.

A 20mm lens with an f/1.4 aperture is a rare combination. It points at specific work: Milky Way and star-trail landscapes, night streets, and interiors lit by window light or lamps. The wide view also suits tight architectural spaces where you cannot step back.

The main trade-off is one fixed focal length and a solid weight on the camera.

The Leica L version weighs 1 lb 6.4 oz (635 g). The barrel measures 3.46 in (87.8 mm) across and 4.38 in (111.2 mm) long, so it sits large on a mirrorless body. The front takes 82mm screw-in filters, and internal focusing keeps the length constant. The physical specification scores 93/100.

The f/1.4 maximum aperture is the reason to buy this lens. It lets in far more light than the f/2.8 or f/4 maximums common on wide zooms. Night and interior work can then run at lower ISO settings or faster shutter speeds. For star fields, a faster shutter keeps stars as points before trails form.

Depth of field behaves differently at 20mm than at long focal lengths. The wide view keeps generous depth even near f/1.4, which helps night landscapes stay sharp from foreground rocks to sky. Focus close, at 0.8 ft (23 cm), and the same aperture can isolate a foreground detail against a soft background.

Eleven aperture blades keep the opening nearly round when you stop down. Out-of-focus highlights then stay smooth rather than angular, which shows up in city lights at night.

The fixed 20mm framing rewards planning. You compose by moving, and distant subjects stay small. This lens favours scenes with a strong foreground or a wide sweep of sky rather than distant detail. The optics specification scores 89/100.

Weather sealing protects the barrel joints against dust and moisture, and a fluorine coating on the front element helps water and oil bead off. Night-sky sessions often run through dew and cold, and that protection suits them. The coating makes the large front glass easier to wipe clean.

There is no built-in image stabilization. At 20mm, hand-held shutter speeds can be fairly slow before shake shows, and the f/1.4 aperture buys speed in low light. The features specification scores 52/100. If you need steadier video or longer exposures, any correction must come from the camera body.

Seventeen elements in fifteen groups include low-dispersion glass, which helps reduce chromatic aberration. That is the coloured fringing that can appear along high-contrast edges, such as bare branches against a bright sky at dusk.

The Leica L version uses three aspherical elements. Their shaped surfaces help correct distortion, the curvature of straight lines that a wide design can produce in architecture. The construction specification scores 69/100.