主题：【原创】Canon的失落（增补版） -- 晨枫

……However this excellent full-frame performance does come at some cost to APS-C users; perceived sharpness is reduced (due simply to the extra magnification imposed by the smaller sensor), and this amplifies the impression of softness wide open. Of course on APS-C the lens still benefits from the 'sweet spot' effects of extremely low distortion and negligible vignetting, so in the grand scheme of things this is something of a case of swings and roundabouts, with different benefits enjoyed by users of each format.

A comparison to Nikon's AF-S VR 70-200mm F2.8G is particularly interesting. The two lenses are near-identical in specification and price, but their characteristics are substantially different. The Nikon lens clearly outperforms the Canon for sharpness on the smaller DX/APS-C format, however this comes at the cost of rather compromised performance on full frame, with significantly higher distortion, vignetting and chromatic aberration, plus extremely soft corners. This leads us to conclude that the two lenses were optimized differently, the Canon for full frame and the Nikon for DX, and illustrates how the different demands of the two formats appear difficult to reconcile in a single lens design.

外链出处