This lens is not to be confused with the 24 -105 f/4 'L' lens, which costs about twice as much. The STM lens has a smaller aperture at the longer focal length (f/5.6 compared with f/4 for the 'L' lens) which makes it not so good for action photography where a fast shutter speed is required. For static shots, the image stabilisation works well, and can deliver sharp hand-held results at shutter speeds of less than 1/100 second even at the telephoto end of the zoom range. The lens works best on a full-frame DSLR (e.g. Canon 5D) because the geometric mean of the zoom range is exactly centred on 50mm, corresponding to the classic standard prime lens full-frame focal length. It is less useful on a crop-sensor DSLR, where the crop effect means that the wide-angle end is not really wide enough. Sharpness is excellent at this price, and is far better than the older 28 -135 IS lens, which until now was the nearest equivalent lens in the Canon mid-quality (non 'L') offerings. Manual focussing with STM takes a little time getting used to, requiring the focus to be active before anything happens when you turn the focus ring, but it seems to be as good or better than USM in speed and quietness. Value for money is excellent, especially with the current Canon £75 cash-back deal. In short, a very impressive lens at the price.