Everything is in the title! After big disappointments from Sigma, I do not regret this purchase because the sharpness is very good, at all apertures and from F4; the manual focus and USM are fine and impeccable build quality. I use it on an EOS 400D with delight. The price difference with the 16 35 f / 2.8 does not seem to me justified under amateur use ... So a goal of bag bottom, usable in all circumstances with enthusiasm