I appreciate this is a question that comes up regularly with new DSLR users, so my apologies for bringing it around again, but I'm struggling to get my head around it... I've been snapping away for the past year on a 500d with an EF-S 18-55mm lens. This week, I purchased a Sigma 24-70mm F2.8 lens (pre-HSM). The Sigma, I'm told, is not designed for APS-C sensors. With this in mind, I expected to look through the viewfinder (with the Sigma attatched) at 24mm and see the field of view I would normaly get from the 35/36mm area of my EF-S lens. However, all through the focal lengths (upto 50mm) they are like-for-like. In fact, 24mm on the sigma actually gives me a slightly wider FOV. Is my new lens in fact designed for APS-C or am I one of the many thousand newcomers confused by Crop Factors. Thanks in advance.