Canon’s EF 20mm f2.8 lens was released in 1992 and is now an almost forgotten needle in the haystack of ultra-wide zoom lenses. Reviews for the lens are mixed, yet it remained in production for over 20 years. Is there a place today for an ultra-wide prime, and for this prime lens in particular?
Not too long ago, 24mm was considered ultra-wide and anything shorter (20mm, 18mm) were exotic. On 35mm SLR cameras, the first ultra-wide lenses required locking the mirror up and using an external viewfinder. Nikon and Canon started releasing short and shorter focal length lenses, first 20mm then 18mm and 16mm, then Nikon went to 13mm. Zoom lenses followed with 20-35mm, then 17-40 and 16-35 and even 11-24mm.
Zoom lenses present a compelling value proposition, one that Canon capitalised on when it released the EOS system in 1987. At launch the widest rectilinear lens was 28mm (a couple of zooms and one prime). Within two years Canon released the amazing-for-its-day EF 20-35mm f2.8 L lens and followed it in subsequent years with 17-35mm then 16-35mm lenses.
Which brings us to the EF 20mm f2.8 prime lens released in 1992. It remained on sale until 2014 so there are many on the used market. It is now an almost forgotten needle in the haystack of ultra-wide zoom lenses.
Intelligent Field Curvature
Many reviews of the EF 20mm lens criticise its off-centre image sharpness (or lack there-of). This often appears in images of flat buildings, test charts and the like. Real images don’t seem to display the problem as much as could be expected from the tests. The reason for this is field curvature.
Field curvature is where the plane of focus of the subject (the field) is not flat. Lenses need to be designed to have a flat field. It’s important when photographing flat objects like maps, so macro lenses are designed for flatness specifically. Most general purpose lenses have a reasonably flat field because for normal subjects at normal subject distances it’s never a problem or not noticeable.
Field curvature is not distortion. Distortion is where straight lines in the subject are bent. Field curvature is where the plane of focus of the lens becomes curved, so areas become blurry.
Wide lenses are often used for landscapes that include the near foreground, with depth of field extending all the way to infinity. With ultra-wide lenses the closest distance can be less than half a meter away in the foreground. For the EF 20mm f2.8 lens Canon developed “Intelligent Field Curvature” where the field of focus is deliberately curved to be closer to the lens away from the centre. This produces better real-world landscape photographs but looks worse when photographing perfectly flat objects, like lens test charts. It appears that the EF 20mm is the only leans to feature this: my guess is that it was misunderstood and the poor results with flat test charts worked against its reputation.
Handling
The EF 20mm f2.8 USM is constructed from plastic with a metal mount and has a solid, quality feel. It has a distance window with IR focus correction mark and depth of field scale for hyperfocal focusing. It uses internal focusing so the lens doesn’t change size during use. Focus is through a ultrasonic motor with full-time manual, and is fast and accurate even on an EOS 620 from 1987.
The lens works equally well on analog film and digital cameras. On digital, Canon provides lens data for the EF 20mm f2.8 so raw files can be processed in Canon Digital Photo Professional software to correct for chromatic aberration, distortion and peripheral illumination, which will improve image quality even further.
Compositionally, ultra-wide lenses require getting close to the subject to fill the frame, otherwise everything looks pretty empty at best. The angle of view is roughly 90 degrees, I’ve found that in street photography you can get close enough to people that they assume you must be photographing something else.
Results
Most of these images in the gallery are analog, made using Ilford HP5 Plus film at 400 ISO in a Canon EOS 620 camera. Most were shot around f8 or f11, and the images taken at Coogee beach used a Hoya R25A red filter. They negatives were camera-scanned using a Canon EOS M6 with EF-S 60mm macro lens, which is why these details are displayed in the gallery. The colour images in the gallery were taken with a Canon EOS 5D.
As the gallery shows, the lens has excellent sharpness and tonality. It is easy to use and focus is fast and accurate.
Conclusion
If you are looking for an ultra-wide lens but don’t want to spend the money that typical 16-35 lenses are going for, the EF 20mm f2.8 USM is an excellent choice. It is plentiful, relatively overlooked, so the used prices are a third of that for a zoom lens.
The zooms offer great value, but the quality and compactness of the prime lens is very attractive, and there is a discipline to using prime lenses that is worth learning.