70 - 200 L series which one?

[LJG]

Even though I am like many and crave low light performance I did the opposite to what most do. I wanted the new f2.8 IS II - until I saw how big and heavy it was. I wanted it mainly for travel, so size and weight was more a consideration than aperture and price. In the end I opted for the f4 IS version. It has lighting fast and deadly accurate auto focus on my 5D2. It is light enough that I can lug it around on my 5D2 with grip and Black Rapid strap without fatigue issues. The IQ is faultless and it works well with my 1.4 teleconverter - it actually reads f5 instead of f4 when it is wide open, not f5.6 like you would expect. I have other lenses to use if I need a wider aperture with a shallower depth of field so it fits my needs well. But that is not to say it will fit your needs. My suggestion is to go into a store and actually try both the f2.8 and f4 versions out, that will give you a much better idea on which way to jump.

[andylo]

I suspect he means smallest aperture possible to retains AF?

Unsure what lens to which we are referring, or if it is a typo.
But, for clarity:

With a x2 extender an F/2.8 lens will have a Max Aperture of F/5.6
With a x2 extender an F/4 lens will have a Max Aperture of F/8.

WW

[William W]

I suspect he means smallest aperture possible to retains AF?

I believe that AF is lost at Max. Apertures smaller than F/5.6, on all but EOS 1 Series Cameras.

So, that's one reason why I posted the clarification: if you have an F/4 zoom and plonk an x2 EF Teleconverter on it, you will lose AF (unless you have a 1 Series camera).

WW

[lincoln]

I sold my f4 to buy the f2.8 IS.
I shoot outdoor sports with it at f8 - f11 so max. aperture is not a concern.
The f2.8 is a large heavy lens, I am reasonably robust but do find the weight tiring at times.
I would suggest that the f4 version will serve you well in most situations barring poorly lit velodromes.

[peterking]

I pondered this question for several months before I bought my 2.8. I deliberately went away from the IS as doing sports you have to turn it off. So far I have only found two occasions when I wished I'd gone for it but as the budget didn't go there I'm happy with what I've got.
I can not stress enough, Do not go the F4 as if you add 1.4 extender as I have you loose one stop and two for the 2X. On my 7D autofocus works all the time.
The weight has not often posed a problem and I'm often at it for min 3 hours.
If you want then PM me and I'd be happy to meet up with you and let you play with my 2.8 and 1.4extender.

[Dittography]

I've just been through the same decision process and was lucky enough to be loaned the F2.8 MkII. All reviews of the MkII were very positive and my loan lens helped confirm that for me. In the end I decided the weight wouldn't be too much of an issue for my intended use. With regards to F2.8 vs F4 and IS or non IS, I decided to go with the philosophy, " better to be looking at it than for it..."
Hopefully once it arrives and I get some real time use with it, my decision proves to be the right one. Either way I'm excited about it's arrival...