Canon EF 20mm f/2.8 USM

There is a version of this lens that lived in real estate agents' trunks for two decades, getting interiors of cramped kitchens to look bigger than they were, and another version that came out only at night to point at the Milky Way. Same glass. The Canon EF 20mm f/2.8 USM was the affordable ultra-wide in Canon's lineup for a very long stretch, 1992 to 2020, and it earned both reputations honestly.

Wide open at f/2.8 the corners are soft and the field is not flat. You see it immediately on a star field: points in the center stay tight while the edges smear into little commas. This is a retrofocus design, which any wide for an SLR has to be so the rear element clears the mirror, and the trade is that perfect edge correction was never on the table at this price. Stop down to f/5.6 and the frame snaps into shape across most of it; by f/8 it is genuinely sharp corner to corner and that is where landscape shooters live. Contrast is moderate and a touch lower than Canon's modern L glass, which some people actually prefer for the gentler highlight rolloff on film.

The 20mm focal length is a specific taste. It is wider than the 24mm that most people reach for first, wide enough that you have to fill the foreground or the frame goes empty and the perspective stretches faces and edges in ways that read as distortion even though the geometric distortion here is mild. Architecture and interior shooters loved it for exactly that reach. Astrophotographers tolerated the soft corners because f/2.8 at 20mm gathers a lot of sky and the price was a fraction of the f/2.8L zooms.

The honest weakness, besides the open corners, is flare. Put the sun near the edge of the frame and you get veiling haze and visible ghosts; the coatings are 1990s coatings and the deep front element catches light. Canon never put a hood in the box, and the EW-75II you buy separately helps less than you want. Shooters who care about backlit work either stop down and accept it or reach for the later L primes.

Today it sits in the used bargain bin in the best way. People cross-shop it against the Canon 24mm f/2.8 (sharper edges, less dramatic) and the older Sigma 20mm f/1.8, and they still buy the Canon because the USM focus is fast and quiet and the whole thing is small and light for an ultra-wide. The 72mm filter thread is worth noting if you shoot landscapes; it is a common size, so a grad ND or a screw-in polarizer is cheap to find, just remember a polarizer across a 20mm angle of view will darken the sky unevenly. One metering habit pays off on a lens this wide: the frame routinely holds bright sky and shadowed ground at once, so meter the zone you care about rather than trusting an average, and let Zone Light Meter place that reading where you want it on the scale before you commit the exposure.