Canon EF 20mm f/2.8 USM

The focal length of this prime lens from Canon is on the edge of ultra wide angle when used on a full frame sensor or the 35mm film it was originally designed for. Even on a cropped sensor, it provides a good angle of coverage. We take a look at how it performs.

Specification

• Focal Length 20mm
• Max aperture f/2.8
• Min aperture f/22
• Construction 11/9 elements/groups
• Angle of view (FF) 84º, 62º, 94º (horiz, vert, diag,)
• Filter size 72mm
• Closest focus 0.25m
• Size 77.5x70.6mm
• Weight 0.405kg
• Mount Canon EF
• Price (SRP) £399.99

Build and handling
As with all of Canon’s prime lenses, the build quality is commendable. The construction ( from the users point of view) is simple with the only control being the AF/MF switch situated to the left of the distance window just forward of the mount. This window is marked in both metres and feet and includes a very usable depth-of-field scale. Forward of this is the manual focus ring, and at 18mm wide there is plenty of room for most fingers. Autofocus is carried out by Canon’s USM motor, which is silent and quick in operation. However, the manual override that the system allows did, on this example, feel a little stiff and not quite as smooth as we are used to. It is one of those qualities that employs ‘feel’ more than others and may well be satisfactory to many although my personal reaction was, ‘This is a stiff one’!

The finish is the usual, hard wearing semi-gloss black and the lens has provision for a bayonet style hood, number EW-75II but this is again an optional extra.

The lens is a compact design that belies the internal workings that operate the focussing without either extending the lens, or rotating any part of it during use. This bodes well for anyone using filters, something that is highly likely given the uses this lens could be put to.

Optical Quality
Wide-angle lenses are known for distorting things and this lens produced a barrel effect of –2.13%. Although we have seen much better figures from more recently designed optics, with modern software this is easily corrected and is not too disastrous. That is the bad news, because all of the other parameters came up to scratch. We have seen often, that lenses designed for full frame cameras can achieve performances at the edge, when tested on cropped sensors, that better the results given for the centre and this is the case with this lens. It is a plus point that augers well for use on FF cameras. It is also relatively consistent throughout the aperture range, another plus point that makes for a useable piece of kit.

Chromatic aberration, although not a concern as it managed to stay below the threshold where it may become noticeable, did show a little anomaly, in that the figures were worse in the vertical plane when the lens was set to wider apertures. This is on measured test results and cannot be seen with the naked eye!

Contrast, along with colour rendition are up to Canon’s usual standards producing an excellent, slightly warm image.

Even on a cropped sensor, the 20mm field of view can capture some dramatic angles. Here at f/8 and ISO 100 on a Canon 300D	Although it is still not quite wide enough for some subjects! The exposure was f/8 and ISO100 on a Canon 300D
The warm rendition of colour from the lens can only aid landscape photographers. Exposure at f/5.6 and ISO 200 on a Canon 300D	Even on a cropped sensor, the barrel distortion is just starting to show in this harbour scene at f/8 and ISO100 on a Canon 300D

Click on each comparision photo below to view full size versions

20mm set at f/8

20mm set at f/2.8

Below is our lens test data. To find out how to use these graphs look at this article: How we test lenses

Verdict
As a wide-angle lens for cropped sensors, this lens falls a little short, with virtually all of the standard zooms giving a wider angle of view. However, on the full frame sensors that Canon are now producing, this lens still warrants its place in their line-up. Nice results combined with ease of use will ensure it will stay there for some time to come.

In summary, the positive points of the EF 20mm f/2.8 USM are:
Good build and finish
Nice focal length on Full Frame cameras
Silent and fast autofocus.
Good image quality

The negative points are:
Not that useful on cropped sensors.
Stiff manual focus ring (on example tested)
Distortion worse than on modern designs (minor point)
Hood not included with lens

Check the latest price of the Canon EF 20mm f/2.8 USM lens here

Test by Ian Andrews www.wildaboutkent.co.uk

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