Canon EF 20mm f/2.8 USM
Lab Test Results
(From Canon lens literature) Ultra-wide-angle lens for serious applications. Easy to hold and carry at 14.3 oz. (405g). Floating rear focusing system. Sharp images are obtained at all subject distances.
July 30, 2008
by Andrew Alexander
The Canon 20mm ƒ/2.8 is a small wide-angle lens, first introduced by Canon in 1992. It uses a design of 11 lens elements in 9 groups, and the use of a floating rear focusing system improves AF performance by not requiring the movement of many elements.
The 20mm ƒ/2.8 was released long before the advent of digital SLR camera bodies, designed to fit a full-size 36 x 24mm film frame. Thus, it will have no problems mounting on either Canon full- or sub-frame camera bodies. On a Canon digital body, it will have an effective field of view of either 32mm (1.6x) or 26mm (1.3x).
The 20mm ƒ/2.8 is still actively manufactured by Canon, takes 72mm filters, and it available from dealers for around $450.
Image sharpness provided by the Canon 20mm ƒ/2.8 when used at its widest aperture (ƒ/2.8) is somewhat soft, a fairly ''lumpy'' profile between 3 and 5 blur units. However, stopped down to just ƒ/4, overall sharpness improves dramatically. At ƒ/4, we note excellent central sharpness (just over 1 blur unit) and very slightly soft corners (around 2 blur units). Stopped down further, there's only marginal improvement at ƒ/5.6, the optimal aperture. At ƒ/8 and smaller, diffraction limiting is already setting in, but it isn't until ƒ/16 that we note any real reduction in image sharpness. Even at ƒ/22, we're back to a generalized softness across the image, between 3 and 4 blur units.
Mounting the 20mm ƒ/2.8 on the full-frame 5D shows off the wide-angle nature of this lens, warts and all. Wide-angle lenses shot wide open typically struggle with image sharpness in the corners, perhaps due to field curvature, and the 20mm certainly isn't an exception. At ƒ/2.8, central sharpness is good at between 2 and 3 blur units, but corner softness is extremely noticeable - 8 blur units, and even going off the chart in the bottom-left of the image. Corner softness is a factor at almost every aperture setting when shooting full-frame, with the possible exception of ƒ/11, where it is (only) 3 blur units in the corners. At ƒ/4, central sharpness is very good, even excellent, but the corners are still extremely soft - between 5 and 7 blur units.
Overall, sharpness performance is best on sub-frame cameras between ƒ/4 and ƒ/8; on full-frame cameras, corner softness is always an issue (more or less), with the most even results coming only at ƒ/11.
The 20mm ƒ/2.8 copes fairly well with chromatic aberration. On the sub-frame 20D, the lens exhibits more CA at smaller apertures than when it it shot wide-open. At ƒ/2.8, CA is rising in a fairly linear manner from 3/100ths of a percent of frame height generally and 6/100ths in the corners, to 5/100ths generally and 9/100ths in the corners at ƒ/22.
On the full-frame 5D, light comes in at a greater angle in the corners (sub-frame sensors focus on the ''sweet spot'' of the lens) and consequently, CA is more prominent in the corners of the image. At ƒ/2.8, the 20mm shows significant CA in the corners - 9/100ths of a percent of frame height - but this reduces significantly as the lens is stopped down. Outside the corners, CA is well-controlled, showing up at only 3/100ths of a percent regardless of the aperture selected.
Corner shading isn't a real problem with the 20mm mounted on the sub-frame 20D. At ƒ/2.8 the corners are 2/3EV darker than the center of the image, and stopping down to ƒ/4 removes the shading almost completely.
It's a different story with the 20mm mounted on the full-frame 5D, however. Corner darkening is some of the most significant we've seen: at ƒ/2.8, the corners are 2 1/4 stops darker than the center. This shading remains an issue at every aperture: 1.5 stops darker at ƒ/4, one stop darker at ƒ/5.6, and levelling out at about 2/3EV darker at all other apertures. If you're looking for this kind of built-in soft vignetting, this may be the lens for you, but otherwise, brush up on your anti-vignetting controls in your favorite post-processing software.
As the 20mm is a fixed wide-angle lens, we aren't surprised to see some barrel distortion, and the 20mm shows a fairly conservative 0.5% barrel distortion in the corners, and 0.3% generally.
The 20mm ƒ/2.8 is a USM lens, so it focuses very quickly and almost silently. Full-time manual focus override is available by simply turning the focus ring at any time.
The 20mm ƒ/2.8 isn't a very good macro lens, with a magnification ratio of 0.19x and a comparatively long minimum close-focusing distance of 25 cm.
Build Quality and Handling
The Canon 20mm ƒ/2.8 USM is a solid lens, coated with a black semi-gloss finish that resists wear and tear. It's built with a metal lens mount and plastic filter thread. It's small but stout, about as wide in diameter as it is long (2.8 in. x 3.1 in.).
The lens only has a few features to talk about, the most noteable being the windowed distance scale measuring distance in feet and meters. A depth-of-field scale is marked for ƒ/11, ƒ/16 and ƒ/22 apertures, and there's also an infrared index marker.
Apart from the focus ring, the only control structure is the manual focus / autofocus activation switch, a simple toggle on the left side of the lens. The focus ring is a ridged rubber, 1/2 inch wide. Manual focus operation on this lens is not as smooth as we have noted with other USM lenses, travelling 90 degrees to cover the entire focus range. The lens accepts 72mm filters, which do not rotate during autofocusing operations.
The 20mm accepts the optional EW-75 or EW-75II lens hood, a plastic petal-shaped hood which adds 1 1/2'' to the overall length and helps the lens to resist flare. It's worth it to use the lens hood, as flare is a noted problem with this lens, showing up as a string of hexagons due to the lens' 6-bladed diaphragm. Note that Canon's literature indicates the lens has 5 blades, but we've confirmed it has six.
Canon EF 24mm ƒ/2.8 ~$300
If you don't need to go as wide as 20mm, the 24mm is slightly less expensive, but lacks the USM focusing. Sharpness is slightly better at ƒ/2.8, but CA, corner shading and distortion are all about the same. Equally questionable on full-frame bodies.
Sigma 20mm ƒ/1.8 EX DG Aspherical RF ~$400
We haven't tested the Sigma 20mm, but it is a full stop-and-a-third faster than the Canon 20mm. The lens doesn't incorporate Sigma's hypersonic motor equivalent (HSM) and takes massive 82mm filters. Better macro, 35mm compatible, and sells for slightly cheaper.
Canon EF 16-35mm ƒ/2.8L II USM ~$1,500
This lens is in quite the different category than the 24mm prime, but it is indeed an option if price is no object. Sharpness, CA performance and corner shading are all much better, and distortion is about the same. Also a USM lens, as a zoom lens it adds the benefit of a wide range of focal lengths.
Canon EF 14mm ƒ/2.8L II USM ~$2,200
If you're a subframe Canon digital SLR camera user and you're desperate for a field coverage similar to the 20mm, the 14mm is the way to go, giving an equivalent view of 22mm. It doesn't come without a significant price tag - almost five times the cost of the 20mm - but the 14mm outclasses the 20mm in almost every way (sharpness, corner shading, distortion), with the exception of some CA issues when shot wide open.
Canon EF-S 18-55mm ƒ/3.5-5.6 IS ~$150
If you don't need the ƒ/2.8 aperture, and are working on a subframe digital SLR, this lens makes a viable alternative. The 18-55mm will provide ƒ/4 at 20mm, and the optical performance at this focal length setting is superb. CA is a little worse, but sharpness is very good, and distortion and corner shading are about the same. Add the benefits of image stabilization, and that you're also spending less for this lens.
The conclusion for this review comes down to recommendations, and we have to segregate the audience into a couple of camps.
For full-frame digital SLR or film users, the 20mm ƒ/2.8 shows off its poorer performance issues, especially for sharpness and light falloff. Whether this performance is poor however, depends on your point of view; if you're looking for a lens which isolates a centrally-located subject by means of sharpness and light falloff, the lens does it spectacularly. If you need even light distribution and even sharpness, the 20mm prime will disappoint, especially at ƒ/2.8. At other apertures, you have a better chance of getting what you need.
For subframe digital SLR users, the lens performs a bit better, but at ƒ/2.8 image sharpness is still poorer than we'd like. At ƒ/4 and smaller, the lens performs wonderfully, so if you don't mind using it at this setting, you really can't go wrong.
The VFA target should give you a good idea of sharpness in the center and corners, as well as some idea of the extent of barrel or pincushion distortion and chromatic aberration, while the Still Life subject may help in judging contrast and color. We shoot both images using the default JPEG settings and manual white balance of our test bodies, so the images should be quite consistent from lens to lens.
As appropriate, we shoot these with both full-frame and sub-frame bodies, at a range of focal lengths, and at both maximum aperture and ƒ/8. For the ''VFA'' target (the viewfinder accuracy target from Imaging Resource), we also provide sample crops from the center and upper-left corner of each shot, so you can quickly get a sense of relative sharpness, without having to download and inspect the full-res images. To avoid space limitations with the layout of our review pages, indexes to the test shots launch in separate windows.
Canon EF 20mm f/2.8 USM
Canon EF 20mm f/2.8 USM User Reviews
6 out of 10 points and not recommended by MichaelShea (8 reviews)Fast and accurate focus; sharp frame centre; attractive colour renderingSoft corners; field curvature; colour fringing
If you were actively seeking a review of this lens, the chances are that you've already seen another one written by Mr Ken Rockwell, who I believe it's fair to say divides opinion on many photography matters. It was he who claimed this lens possesses so-called 'Intelligent Field Curvature' and that its most obvious limitations can be overcome with good composition, careful selection of focal points and then the application of modern lens profiles when post processing. Unfortunately most of this is nonsense.reviewed March 4th, 2015 (purchased for $345)
It is right to draw attention to field curvature, as photozone.de have also done, because it compromises the sharpness qualities and general usefulness of any given lens. There is nothing intelligent about having a focal plane that isn't straight and it's particularly inconvenient if you are predominantly a landscape photographer like me. In short, it's impossible to obtain pictures that are sharp from corner to corner with this lens.
Being pre-warned about this issue is helpful however, as it forces you to take action to mitigate the potential damage. The best thing you can do in my opinion, whether you're producing a landscape, or anything else for that matter, is not to choose a focal point that is too far into the distance, or else your foreground is going to be noticeably out of focus. But be warned that even if you follow this advice, the edge of the frame will not be sharp in the far distance anyway. Go to f11 to achieve an improvement in the corners, but the results still won't be great or even very good.
I have made a conscious decision to work within the limitations of the lens and to some degree follow Mr Rockwell's advice, by ensuring that nothing of great interest is left in the far distance especially at the corners of the frame. To some extent this will improve my photography technique, because in order to make my pictures more appealing I'll get even closer to my main subject, which is never a bad idea with a wide-angled lens anyway.
Post processing software removes vignetting at large apertures and any of the chromatic aberrations that you will surely notice at all apertures when your light contrast is high. It does absolutely nothing for the curvature issue though and you might have thought it strange that Canon would have brought a lens out in 1992 before the onset of the digital age in anticipation of such software. And of course they didn't. To be honest, the lens should be superseded by something on a quality par with the image stabilised EF 24mm f2.8 model and then everyone would be satisfied, including me.
I don't want to appear totally negative about the lens because I fully appreciate that there are other uses for it besides capturing scenery. Colours are typically Canon, focus is fast and completely reliable and it's reassuringly solidly built. The lens balances well on my 5D3, which means it's very easy to keep still. My main reason for buying it used at roughly half the recommended retail price of a new one is that I wish to keep my kit fairly light and small and it's suitable for that purpose. I don't own any Canon zoom lenses, but I'm fairly sure that optically it offers no advantages over many average to high-end zooms out there by various manufacturers.
So it's not all bad news, but this is not a lens with a perception that is going to improve with age. With Canon about to launch a 50 megapixel camera I feel its failings will be laid bare once and for all and it won't survive in general circulation for very much longer.
8 out of 10 points and recommended by Creyr Glas Lightworks (10 reviews)fast focusing even in low light, wide, great colorsI occasionally really miss shots because of focus being off.
I shoot with it on a Canon 40D. I bought this lens for shooting nightclubs and bands, in locations I did not want to risk taking my 24-105L lens. I intended this to be a cheap purchase that I could use at F4 to F5.6 combined with a bracket mounted flash to shoot clubs and events. So far, it has delivered excellent results, even moreso than I expected. I knew I was perhaps taking a risk on this lens, but I have not been let down, and I feel the lens is a perfect choice in the end for this kind of photography. Images are vibrant and crisp, with none of the flatness my competition gets with their zoom kits. I can just fire away, and the speed (at 2.8) allows me to get a bit more out of shots in low light without using the flash. The sharpness is quite acceptable for these candid photos. The IQ is hard to judge given the conditions I shoot in. I would like to give this lens a solid 8.5, but I will settle for lowering it to an 8.reviewed March 22nd, 2010 (purchased for $450)
Feel free to check out the images here:
4 out of 10 points and not recommended by MalteR (4 reviews)good case, fast AFvery poor corner sharpness, generally unsharp when not stopped down
Those who believe primes tend to outperform zoom lenses in general, should take a closer look on that one to find out they are wrong. Sorry, folks, this is one of the worst lenses i ever had.reviewed January 4th, 2010 (purchased for $350)
I must admit i tried to use it mainly for architecture and landscape photography on a full format Canon 5D/Mk II and the first thing i demand from such a lens is sharpness. Not a good idea, you may use it wide open or stopped down, you won´t get the corners sharp while only a small area around the center looks like one expect it from such a lens, tack-sharp. It also suffers from chromatic abberations.
Okay, this might not be a problem if you use it on a body with smaller sensor and only publish your photos on a 15" screen. On the other hand, the lens is fast both in terms of AF and using it at 2.8 - but that´s not what i demand from a prime lens in this category.
I found the 17-40mm Canon Zoom outperforms this one in nearly every respect. And if you are looking mainly for a sharp superwide lens, not an extremely fast one, a Zeiss 21mm or 20mm, even an old, used one from GDR production, will demonstrate how bad this Canon is.
8 out of 10 points and recommended by Isaacarus (2 reviews)nice size on a 30D, decently fast aperture, nice fast AF, the only "reasonably" wide prime for cropnot as fast as im used too(1.4) not REALLY sharp till at least f/9.0, ok from about f/4.5, vignetting is very bad at 2.8 even on crop!
i brought this lens as i definitely prefer primes over zooms and i needed something "wide" for my 30D and going by the reviews and the size of the sigma 20mm i was a tad put off.reviewed April 16th, 2008 (purchased for $340)
now compared to my other two primes(50 1.4 and 30 1.4) this lens is comparably on the slow side(2.8) which is something ill need to get used too :( at least its about the same size as the 30mm, just a little bit longer and about the same width, though im happy its a bit lighter :)
AF is really nice! its very fast, very accurate and of course silent ;) its definitely faster than the HSM of the sigma and the micro-USM of the 50mm. it also helps that it has a fairly short focus travel to help out the speed.
of course now to the all important image quality...
at 2.8 the image isnt the sharpest obviously, but i wouldnt hesitate to print a4's from it, maybe even bigger? of course the corners are semi soft, but the center is actually quite reasonable for a lens wide open.
as you stop down to between 3.5 and 5 the image gets a lot better, and the corners come into the same league as the center at around 5.6 but they are definitely acceptable from 4.5 onwards.
Of course the further you stop down the better it gets.
between f 9 and 11 is its "sweet" spot, with both the corners and centre about the same very good res making it ideal as a landscape or architecture lens.
i tried a few shots today of my g/f and i would definitely say; do NOT use it as a portrait ;) what they say about making things bigger is true, it is not flattering for people, especially girls ;D
so if you can handle having to stop down a little bit, which is required for DOF anyway, and not using it indoors without a tripod or for where very high res is required i would reccomend it.
if you need something to use wide open all the time and still require high levels of detail, i honestly couldnt reccomend this lens.
the main reason i got it was personally i prefer primes(even this one ;) ) and also, i got it at a GREAT price 2nd hand so i couldnt resist (430NZD/340USD 2nd hand compared to over 800NZD new! :O )
if your looking for a good wide angle with good res, id suggest the tamron 17-50 as it goes wider, is the same aperture, roughly same size/weight and has probably a higher detail res from wide open... of course its not FF compatible if thats your niche.
oh well, i guess thats the price you pay for what is essentially a super wide for the 35mm it was designed for all the way back in 92 so until someone releases a sharper wide angle prime at a similar price point, guess i wont be getting rid of this one, especially not considering it may be used FF within a year and i lok forward to the super wide FOV! :D
on a side note, it makes a great compliment as a prime kit to the aforemention 30 and 50 and soon to be 85... :D