Equivalent to a 16-35mm zoom on a 1.6x FOVCF (Field of View Crop Factor) camera,
the Canon EF-S 10-22mm f/3.5-4.5 USM Lens fills a gap in Canon's ultra wide angle lens lineup.
EF-S is Canon's moniker for Short Back Focus.
The distance between the film (sensor) plane and the rear of the lens is shorter than it is in an EF lens.
Many question the longevity of this standard.
My expectation is that it will be around for a long time - easily long enough for most people to get their desired value from a lens.
Knowing Canon's excellent-at-that-time 16-35 L
and 17-40 L
lenses had some shortcomings at their wide end (namely some barrel distortion and soft corners), I was apprehensive about a non-L Canon 10-22mm Lens.
Softening my apprehension was knowledge that Canon was including three Aspherical lens elements and a
Canon L Lens Series-like Super-UD element.
To cut the chase, I must say that I am very impressed by the
lack of barrel and pincushion distortion in the Canon EF-S 10-22mm f/3.5-4.5 USM Lens.
It is not perfect, but very good for this extreme wide angle focal length range.
There is a slight barrel distortion at 10mm moving slowly to a slight pincushion at 22m.
Slight enough distortion for me to be happy with the results.
On the sharpness issue, I found the Canon EF-S 10-22mm f/3.5-4.5 USM Lens to be a very good performer.
Keep in mind that when shooting at these focal lengths, details tend to get extremely small.
Our DSLR sensors struggle to produce sharp results when details get down to the pixel or couple-of-pixel size.
The Canon EF-S 10-22mm f/3.5-4.5 USM Lens is a little soft at 10mm with some softness in the corners.
Sharpness at 10mm improves slightly when stopped down, but the corners retain some of their softness.
At 16mm, the Canon 10-22 has decent sharpness wide open and improves little when stopped down.
Corners retain some softness until stopped down beyond f/4 or so.
Sharpness at 22mm was good and again, improved little stopped down.
Corner sharpness was best at 22mm.
Resulting images take post-process sharpening well.
Wide open (especially at 10mm), the 10-22 shows strong vignetting.
Stopping down or increasing the focal length reduces vignetting.
Flare is another common enemy of an ultra wide angle lens.
An wide front element combined with an ultra wide focal length can spell flare problems when the sun is out.
The good news is that the Canon EF-S 10-22mm f/3.5-4.5 USM Lens controls flare very well.
Usually, if the sun was not in the frame, flare did not exist.
CA (Chromatic Aberration) is a common lens quality differentiatior.
Although some CA is present in the 10-22 (most notable at 10mm in very high contrast situations), it is very well-controlled.
Bokeh? Well, Canon claims the Canon EF-S 10-22mm f/3.5-4.5 USM Lens has a circular aperture design for great stopped-down out of focus highlights.
Actually getting stopped down out of focus highlights in normal shooting applications is not easy with a lens of this focal length range with not-wide open aperture settings.
So, a good feature with relatively low importance for most uses for this lens.
A very deep depth of field can be a welcome feature itself.

Pictured above from left to right are the Canon EF 15mm f/2.8 Fisheye Lens, Canon EF 14mm f/2.8 L USM Lens, Canon EF 14mm f/2.8 L II USM Lens, Canon EF 16-35mm f/2.8 L II USM Lens and Canon EF-S 10-22mm f/3.5-4.5 USM Lens. Below are the same lenses (sans the 14mm L I) with their lenses hoods in place.

Build quality of the Canon EF-S 10-22mm f/3.5-4.5 USM Lens is very nice.
It feels reasonably solid and well made, but is not heavy or large.
The size and weight make the 10-22 a nice match for the current EF-S mount DSLRs.
A metal lens mount rounds out the quality build.
The Canon EF-S 10-22mm f/3.5-4.5 USM Lens is not weather-sealed, but neither are the currently available EF-S mount DSLRs.
Although the 10-22 does not extend with focusing or zooming, the inner elements move in/out slightly.
The 77mm filter size allows filter sharing with many of the other L-zooms.
I should also note that a Circular Polarizer Filter may produce an uneven result at these wide focal lengths.
Expect to see a small amount of additional vignetting at 10mm with a wide open aperture when using a standard sized (non-slim) filter.
Many people don't mind this, but a slim filter avoids the problem.
The Canon EF-S 10-22mm f/3.5-4.5 USM Lens's focus speed is fast and the focus sound is very quiet.
We can thank Ring USM (and a short infinity focus distance) for these features.
Minimum focus distance is about 9.5" (241mm) for the 10-22.
With a maximum aperture that ranges from f/3.5 to f/4.5, the 10-22 is a medium-fast lens.
The wide focal lengths make handholding easier.
Flash coverage of the Canon EF-S 10-22mm f/3.5-4.5 USM Lens' complete focal length range requires an
external flash unit.
Even with an external flash, a
Sto-Fen Omni-bounce
may be required for close work.

Pictured above from left to right are the Canon EF-S 18-55mm f/3.5-5.6 Lens, Canon EF-S 60mm f/2.8 USM Lens, Canon EF-S 10-22mm f/3.5-4.5 USM Lens, Canon EF-S 17-85mm f/4-5.6 IS USM Lens and Canon EF-S 17-55mm f/2.8 IS USM Lens. The same lenses are pictured fully extended below.

The Canon EF-S 10-22mm f/3.5-4.5 USM Lens' focal length range fits nicely below Canon's popular 24/28-XXmm general purpose lenses such as the
Canon EF 24-70 f/2.8 L Lens.
These two lenses (or other similar combinations) could satisfy all focal length needs below 70mm for many people.
Even if your main lens is 16/17-XXmm, the 10-22mm is much wider and would make a useful addition.
In my opinion, shooting at 10mm requires more skill on the part of the photographer than shooting with longer lenses.
The Canon EF-S 10-22mm f/3.5-4.5 USM Lens is even wider than the Canon EF 15mm Fisheye Lens on the same camera.
Composition at this focal length becomes more difficult.
As this angle of view takes in a lot of background,
care must be taken to make it look good - and it probably will not be blurred out of focus.
Watch out for your shoes and shadow - they are easy to include in the 5% of the picture missing from the current EF-S DSLR's 95% viewfinders.
Close-up perspective at 10mm can result in wild and dramatic photos.
This angle of view opens up a great opportunity for creativity.
But if you want parallel lines to remain that way, you must shoot them from an exactly perpendicular angle (or fix them later during post-processing).
This perspective distortion is up to photographer to control or dramatize as desired.
Architectural photography is one 10-22mm use with many parallel lines.
Interior photography is another similar good use for this lens.

While there is no law against taking pictures of people with the Canon EF-S 10-22mm f/3.5-4.5 USM Lens,
they better be self-secure, fun-loving and smaller than you if they are going to see the results from close shots!
You can make monsters out of your angels.
Everything that sticks out will be greatly enlarged - especially noses.
Fortunately, Brittany fits my 10-22mm people subject criteria.
On a more serious note, wide environmental portraits and other people pictures taken from a longer distance can yield fine results.
In summary, I think the Canon EF-S 10-22mm f/3.5-4.5 USM Lens is a very nice addition to the Canon lens lineup.
(I just wish I could use it on my non-EF-S mount DSLR.)
Canon EF-S 10-22mm f/3.5-4.5 USM Lens Sample Pictures ...

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Canon EF-S 10-22mm f/3.5-4.5 USM Lens at Adorama
Canon EF-S 10-22mm f/3.5-4.5 USM Lens at 17th Street Photo
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