Camera Upgrade?

[Andrew Garrard]

I'd expect some autofocus benefit from f/2.8, I just wasn't expecting f/1.8 (in the context of the 18-35) to do much beyond that for the AF system! (Don't get me wrong, by all accounts it's a very high quality lens, I'm only talking about what the aperture will do.)

 

Aperture always helps with isolation, but so do proximity and focal length. It always depends how much isolation you want! I've not shot with the 17-50, so I don't really know what it can do; f/2.8 is usually plenty for head-and-face portraits, but I've not looked into the close-focus-vs-focal-length behaviour of the Sigma if you really want to isolate finger prints, for example. That may be entirely irrelevant depending on what look you try to achieve.