Im mostly new to all this so sorry if my question is an easy one but want to make sure im thinking the correct way. Im interested in a Sigma 17-70mm lens. Now there is an f2.8 and a f2.8 to 4.5 version. The f2.8 will be a fast lens at all stops but a small DOF. The 2.8 to 4.5 lens will not be as fast on the long end but have a larger DOF. Is this the correct way of thinking or am i all wrong?
Oh and a word on HSM. If my body has a motor is HSM needed and/or just an added bonus to have HSM
Oh and a word on HSM. If my body has a motor is HSM needed and/or just an added bonus to have HSM