I thought about the 85 1.8, but since I already have 24-70 covered, I wanted to go a little longer, hence the 100 f/2.
I think the 85mm to 100mm range is just about perfect for portraiture on a crop sensor camera.
You can get the 135mm f/2.8 if you're planning to go full frame. That move gives you 1 1/3 more relative dof compared to a crop camera. Thus, wide open, the 85mm f/1.8 on a crop is nearly the same fov and dof as the 135mm f/2.8 on the 5D.
It's a great lens - and the very end for portraiture on a crop camera for me. Too much compression after that, and flat faces aren't a good thing for portraiture. With that said, there are always situations when this rule can be broken - I've even seen portraits done with a 300mm lens.
, but my priority is to use this for portraits.



