Quote Originally Posted by cxr
deciding between the f4 IS or f2.8 IS Mark II. If I could justify the price of the f2.8 IS Mark II, i might be tempted to get that.

I can't tell you if you can "justify" it , but I think the pros and cons are pretty clear


Cons: weight, price


Pros: work in half as much light, narrower DOF/increased background blur. (There are also af advantages to f/2.8, but IMO that is a minor issue).


I think it depends heavily on what you shoot (and how easily you can part with the money, of course).


I use the f/2.8 II on the 5DII, and I really like the narrow DOF for portraits. On the 5DII, it is equivalent to about 45-125 f/1.75 on a crop body, so you're getting the speed and IQ of a prime used on an APS-C with the versatility of a zoom in a range that is- at least for me- ideal for portraits.


On the other hand, full frame f/4 is already very usable and it is much cheaper, and you're giving up little to nothing up in terms of IQ. If you're shooting in good light and don't need the narrow DOF, f/4 may be the way to go.