Quote Originally Posted by wickerprints


I'm not sure if you're understanding what some people mean by "distortion."


Usually when photographers speak of lens distortions, they mean geometric distortions of a nature that deviates from a rectilinear projection--that is to say, certain features that form straight lines in the subject are imaged as curved lines. The two most common terms to refer to this type of distortion is "barrel" and "pincushion," the former describing a curvature outward, and the latter describing a curvature inward.


However, based on the images you have posted, what you appear to be describing as "distortion" is actually the natural consequence of a rectilinear projection. It is called "perspective distortion" but it is the inescapable result of trying to project a curved field of view onto a flat plane. The shapes of the buildings taper upward not because the lens has high distortion, but because it is a geometric necessity to keep the straight lines of the subject straight on in the image. The same effect is observed if you stand next to a tall building and look up the side--your eyes will perceive the sides of the building as two lines converging near the top, even though in reality they are parallel.


Distant objects appear smaller than closer objects. This is a critical property that the human brain uses to infer the distance of an object.


The wideness of the 17-40/4L lens is such that this rectilinear perspective is very pronounced. Our eyes do not have such a short focal length and therefore we are unaccustomed to this extreme wide-angle perspective. The tapering of the buildings is because you have tilted the camera slightly upward--just like the skyscraper example I mentioned.


The barrel distortion @ 17mm is there and it is noticeable, but it is very subtle in the images you posted. It is easily corrected in Canon's DPP software. It is not a lens defect--it is part of the compromise of designing a wide-angle zoom lens. Many lenses, including the 24-70/2.8L, 24-105/4L IS, 16-35/2.8L II, and yes, even the EF-S 10-22, exhibit barrel distortion at the wide end and pincushion at the long end. Primes show less distortion but it too is present. But I again emphasize that the barrel/pincushion distortion we're talking about here is NOT what you are seeing in the attached images.


If you purchased the 10-22, you would find your "distortion" (which is really a property of projecting a curved field of view onto a flat plane) to be even more dramatic, as the 10mm focal length is dramatically wider than 17mm.
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Wickerprints, thanks for this explanation, it is absolutely fantastic[Y] I actually purchased 10-22mm recently and being a new in photography had a bit of an adjustment issue with it, I was shooting duds for a while until I figured the whole tilt problems, or in other words "operator error" [:$] It took me a while to figure it out what you put so eloquently and easy in your explanation. Thanks again. You guys are the best!