Canon EF-S 10-22/3.5-4.5 USM Lens Review
Focusing is virtually silent due to the ring USM motor. I measured the time to focus from infinity to 0.24m (closest focus) at 300ms (0.3s). The manual focus ring is typical of Canon full time manual focus, smooth and well damped. There is a focus scale with makings for 0.24, 0.4 and 1m (also 0.8ft, 1ft, 1.5ft and 3ft) as well as infinity. There is no depth of field scale or infrared focus mark. The lens can be focused "past infinity" to allow for compensation of any thermal effects.
Maximum and minimum apertures at marked focal lengths are given in the table below:
Values enclosed in [square parentheses] are the full frame equivalent focal lengths
There is very little noticeable vignetting at any focal length or aperture, which for a superwide lens is excellent performance. Below is an example shot at 10mm both wide open at f3.5 and stopped down to f16. While you can probably just detect some vignetting at f3.5, it's really very slight.
With a normal filter, even at 10mm I saw no vignetting due to the filter. However when I mounted a Tiffen 77mm circular polarizer (PL-C) on the lens, I did see slight corner vignetting at the 10mm setting as shown below. At 11mm I saw no probelms. Note that for vignetting caused by a filter, stopping down makes the extent of the vignetting less.
If you're a big fan of polarizers and superwideangle shots you might want to get a "thin" polarizer for this lens. The only caution I'd have here is the general one that if you have any blue sky in the shot and adjust the polarizer for maximum effect, this will usually result in uneven sky brightness with any wide and superwide lens. The shots above were with the polarizer set to minimum effect. If you avoid using at polarizer at 10mm, you should be safe from vignetting even with a normal polarizer from 11-22mm.
It's interesting to note that the vignetting I saw appeared mostly at the top corners of the frame but not so much the bottom. Really, for a perfectly alligned optical system it should the the same at each corner.
Distortion is low for such a superwide zoom. There's a touch of barrel distortion at 10mm but by the standards of similar lenses, it's at a pretty low level.
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