Canon 85mm 1.8 vs Sigma 70-200 2.8?

That is an interesting question.  I currently own the 85mm 1.8 lens and I am looking at adding this one to my camera bag.  My lens choices are similar to yours so far:  Tamrom 17-50mm 2.8; Tamron 10-24mm; the "nifty fifty' 1.8; and the above mentioned 85mm.   I don't think that they 70-200 is going to get as much use as the 17-50 which is my main "walk around" lens, but last year I found myself shoot my 6 year old's soccer match with an old Canon 70-210 f4 from 1988 and I realized that I needed something better.  I am sure that the situation is going to come up again and again where I will want the extra reach of the 70-200.  For example, this summer at the beach I wanted to get my kids playing in the sand with the background blurred and shoot while not on top of them.  The 85 did the trick but I would have preferred a 70-200 because at 1.8 and ISO of 100 I was still hitting the upper limit of the shutter speed (1/4000 - 1/8000).  Once you have to stop down anyway to 2.8 might as well have a little more flexibility even at the cost of "prime sharpness".

That is my 2-cents worth.  I hope that helps your thought process.

By the way, if/when I do get this 70-200 I am not getting rid of my 85mm.  It is one of the sharpest lenses I own and it fits well in my bag when I am not travelling 'heavy'...

~Peter

I have a Sigma 70-200/2.8 HSM (forgot which generation), and a Canon 100/2.
I like the 100/2 much better, better quality and much lighter. I also have a Kenko 1.4TC and prefer this with the 100/2 over the Sigma.