I bought it to replace tokina 16-50 / 2.8, because everything was fine on 400D, but on 50D it no longer pulled on resolution, it started to lather. 17-55 / 2,8 solved the issue of sharpness, incl. on open apertures. It seems that from the non-L series this is the only zoom that pulls 15 megapixels. The stub helps a lot. With another 50mm lens, shutter speeds of 1/80 and longer give blur (alas, the pixel density affects). And with a stub - 1/15 -1/10 is not a problem. At a wide angle, you can shoot at longer ones, up to 1/4. They say it's a vacuum cleaner. No, I haven't vacuumed anything in six months. The design is solid, but I would like better. In general, the best staffer for crop :) Who needs aperture ratio, resolution of a multi-megapixel matrix, speed and focusing accuracy - you will not regret it.