The image quality is very good even at full aperture. However, is spoken in various tests and in the Amazon reviews of always knackscharf up in the corners. I can not quite confirm, at least not to the image corners. The new push is in the border regions (and also toward the middle) unequivocally significantly sharper than the 17-40mm. However, it is still at 16mm - well dimmed a little - not knackscharf in the outer corners. The sharp edge areas extend much further, however, in the corners as the 17-40mm.
The fact that the lens on delivery is NOT dustproof, has me very disappointed, leading to my decision to the objective "only" to give 4 stars. The suggested by Canon for its L-lenses dust tightness is only achieved with a filter attached (s. Note the operating instructions). Without attaching the filter, the lens is not dustproof. Buying a high-quality protection filter (most "slim") proposes again with 60-80 euros.
It's hard to make a fair evaluation. 4 or 5 star? In absolute terms I forgive good 4 stars, relative to the 17-40mm I would, however, can also assign 5 Stars.
At present there is probably no alternative in terms of image quality in this focal length range. The 14mm fixed focal length of Canon or the TS 17mm are well for most amateurs across the Affordable. For this reason, a strong buy recommendation for this lens.
