Introduction

Canon EF 20mm f/2.8 USM is one of the oldest lenses in Canon's EF lineup, originally released in early 1992. And up until recently, this was the widest, non-fish-eye lens in Canon's arsenal (the company recently released an even wider lens - EF 14mm f/2.8L USM). Priced at about US$400 (as of June 2007), the lens is certainly affordable to the masses and is often considered by landscape and architecture photographers. The lens is manufactured in EF mount, making is suitable for both full-frame and APS-C type cameras. On a typical APS-C dSLR with 1.6x crop ratio, the field of view of the lens resembles that of a 32mm lens on a full-frame body.

The optical construction of the lens consists of 11 elements in 9 groups, including a single floating glass element. The lens is not the lightest or most compact UWA lens available on the market, weighing 405g (14.3oz) and measuring 77.5x70.6mm (3.1x2.8"). The build quality is similar to that of other consumer grade lenses in Canon's lineup (read average build quality) - the barrel is made of durable plastic, which, while not flimsy at all, might still leave you with a 'cheapo' impression. Focus ring is fully rubberized and is very smooth, but the lens does not have an aperture ring and all aperture settings are controlled directly from the camera. The lens features a true inner-focus design (the lens cams do not extend during focusing) and sports a fast and silent USM-type AF as well as a full-time manual focusing system (both controlled by an AF/MF switch on the side of the lens barrel). Note that the front glass element of the lens is quite bulging, so you should definitely consider using a protective filter or at least a lens hood to minimize the chance of scratching it accidentally. The filter size is 72mm, and since the front element does not rotate during focusing, you will be able to attach a polarizing filter to the front of the lens.

 

Image

Manufacturer's box contains Canon EF 20mm f/2.8 USM lens, front and rear caps and warranty/registration card. The lens is compatible with Canon's EF 12 II and EF 25 II Extension Tubes and also accepts gelatin filters with an optional Gelatin Holder Adapter.

 

Summary
Lens Composition 11 elements in 9 groups
Angular Field 94 degrees
Minimum Focus 25cm/0.8ft
Focusing Action AF/MF, USM
f-stop Scale f/2.8-f/22, camera-controlled
Filter Size 72mm
Lens Hood EW-75II (optional)
Weight 405g/14.3oz
Dimensions 77.5x70.6mm/3.1x2.8"
Lens Case LP1214 (optional)

 

Field Tests

This is one lens that is rather hard to characterize in a few sentences because of a somewhat uneven overall performance. Image quality was reasonably good under some circumstances. Note here the word 'some'. On APS-C type camera images were visibly soft at f/2.8 around borders (and on a full-frame body they were even softer). Quality did improve somewhat with stopped down aperture but there's no magic here - most lenses are sharper when stopped down and Canon EF 20mm f/2.8 USM is not really an exception here. Color rendition was more or less accurate, but images lacked contrast.

 

Vignetting @ f/2.8 - full frame vs 1.6x crop
Vignetting @ f/2.8 - full frame vs 1.6x crop

 

Vignetting was somewhat on a higher end at f/2.8 with a full-frame camera and less so with an APS-C one, but gradually got better and was pretty minimal at f/4 and beyond. The lens also showed visible barrel distortion, which while expected from such a wide angle lens, is still disappointing. The lens was also prone to flare at the widest aperture setting. AF was pretty accurate and fast throughout the tested aperture settings.

 

Canon EF 20mm f/2.8 USM image gallery

 

Lab Tests

Please note that MTF50 results for APS-C and Full-Frame cameras are not cross-comparable despite the same normalized [0:1] range used to report results for both types of cameras.

 

Canon APS-C: Canon EF 20mm f/2.8 USM showed somewhat mixed results in the lab. Center performance was outstanding from f/2.8 throughout the tested aperture range (peaking at f/5.6). Unfortunately, border performance is rather disappointing - it's not the worst I have seen but certainly is not inspiring either (for a fixed focal lens that is). At its best, the lens would give you outstanding 11in and decent 16in and 19in prints, which is a decent performance, except that we expect more from a prime lens these days. Conclusion? Combination of excellent center and average border performance makes it hard to render a definitive decision. The lens should probably remain on your 'maybe' list until you find an alternative that clearly outperforms Canon EF 20mm f/2.8 USM.

 

MTF50 (Line Width/Inch on the Print) @ 20mm
MTF50 (Line Width/Inch on the Print) @ 20mm

 

Normalized raw MTF50 @ 20mm
Normalized raw MTF50 @ 20mm

 

Chromatic aberration was well under control in the center (less then 0.5px throughout the tested aperture range), but was more pronounced around borders, where it varied from ~1.7px to ~1px. For a prime lens this might seem a bit on a higher end until we recall that we're dealing with am ultra wide angle lens here.

 

Image borders @ 20mm (100% crop): f/2.8 vs f/8
Image borders @ 20mm (100% crop): f/2.8 vs f/8

 

Canon FF: The lens performance around borders on a full frame 5D was outright miserable - wide open or stopped down, borders were basically iffy throughout the entire tested aperture range. Image quality in the center was the only bright spot here - at f/2.8 center was reasonably sharp and quality improves once you stop down, reaching a respectable level by f/5.6. Conclusion? Performance of the lens on a full-frame body only complicates things - should you ever go after a lens with a decent center and lackluster border quality?

 

Normalized raw MTF50 @ 20mm
Normalized raw MTF50 @ 20mm

 

Chromatic aberration around corners on a FF body was also slightly higher then on an APS-C camera - at f/2.8 CA averaged ~2px, but dropped to ~1px once stopped down to f/5.6 and beyond. Chromatic aberration in the center was pretty nominal, ranging from ~1.2px at f/2.8 to ~0.5px at f/8.

 

Image borders @ 20mm (100% crop): f/2.8 vs f/8
Image borders @ 20mm (100% crop): f/2.8 vs f/8

 

Alternatives

A good high quality ultra wide lens is a rarity (in Canon's EF mount at least) and this is one of the reason for the resurgence of interest for using alternative mount lenses (such as Zeiss and Leica) on Canon's EOS bodies. That is also the reason why it would be hard to find a (native mount) lens that would significantly outperform Canon EF 20mm f/2.8 USM. Within the Canon's camp, you might want to take a look at Canon EF 24mm f/1.4L USM (assuming you're OK with a slightly narrower angle) and at Canon EF 14mm f/2.8L USM, which is the widest prime lens currently manufactured by Canon. Outside of the Canon lineup, you are limited to a couple of UWA lenses manufactured by Sigma, all of which will be playing a catch up to Canon EF 20mm f/2.8 USM. (I'm not considering fish-eye lenses in this section).

 

Recommendation

There are not that many (better) alternatives to Canon's EF 20mm f/2.8 USM that fall within the same price range and at the same time deliver superior performance. That might be the reason to seriously consider this lens for your ultra wide photographic needs, despite somewhat lackluster performance that the lens showed around borders and level of various artifacts at the widest aperture setting. Those of you not willing to accept the trade-offs, prepare to either spend 3x more for one of the above-mentioned Canon L lenses (EF 14mm f/2.8L USM or EF 24mm f/1.4L USM) or expand your search to UWA zooms.