I'd rather have a 70-200 L IS F4 on a 5d II than have the sigma 70-200 2.8 on anything else. Iso 3200 from the 5d II > iso 1600 from lower models (and all of Sony), and the difference is only a stop sir.

and this. 100mm f/2 is really great lens, pretty much the same as 85mm 1.8, that would be something to consider also. but if you would go with the 50mm, i think the 100mm would be better choice. 50mm 1.4 + 100mm f/2 would be better choice than 70-200mm zooms imo, then save up for some wide angle zoom like 17-40 or 16-35 and you have pretty much all you will ever need(for the usage of full frame camera)

it doesent matter if 5d has 3200 iso better than lower models with 1600 iso. both lenses have their uses and whether you like f/4 or f/2.8 it depends on your needs, so you cant really compare the two lenses. its not about 1 stop more light, its about blurring the background, getting right dof, stopping the motion etc. many of the times you will need to shoot at maximum ISO that you are comfortable with, when you need to stop motion, you need like 1/200th shutter speed. now if you are using f/4 lens over 2.8 and want to stop the motion, 1/200th sec would give only half the light in, so you would need to use 12000iso over 6400, and that will make pretty huge difference to the picture

I always used primes on nikon but i think the sharpness of that zoom is just worth the price.. It is much more flexible(which is good to me) than a prime and the quality is gorgeous.
The only thing i'd need the 2.8 for (since i'm not shooting indoor sports) would be to blur the background more but are you sure you need more than this:

http://photography-on-the.net/forum/showthread.php?p=11764176


As speaking for the future, i'll save up some money for the 135L though i guess or a 35 1.4

This post was edited by Verdena on Feb 3 2011 06:58pm

take some distance to the subject and you will notice bigger difference between f/4 and f/2.8 @ 200mm. f/4 does some situations, but after a while im sure you will start to see what the f/4 is lacking with the dof

This post was edited by Antichrist- on Feb 3 2011 07:00pm

I'm not doubting that, you forget there is 800 euro between the 2 things aswell and that's probably why f4 lacks something^^

im talking about any 70-200 2.8(sigma, tamron, canon what ever) vs 70-200 f/4 IS.

^This. Sometimes even f/2 is too slow in low light.

Do you really need to reach of a 70-200?

For that price, you can probably get probably get a used 50/1.4, 85 1.8 and a 100/2. good combo with excellent IQ that can tackle many things.

I often make outdoor shots of people, a prime can't be my first choice.

Then you just answered your own question. I would go with a sigma 70-200 2.8 II TBH.