If You Had To Choose: 1 more f stop or IS?

I just have one IS lens and honestly I can't tell that much difference with the IS off or on.

Last year I asked myself the same question. My biggest difficuly was chosing between the 24-70 f2.8 and the 24-105 f4 IS. Eventually I chose the 24-105 f4 IS. My reasons revolved around a)- the extra focal length range; b)- weight for my walk-around lens; c)- 1 stop faster (f2.8 vs. f4) can be achieved by shooting ISO200 vs. ISO100 (or 400 vs. 200, 800 vs 400 etc.).

A few weeks ago I went to a tractor-pull which was held just down the road from where I live. My main aim was to become more familiar with my equipment (see list below - I only bought it about 6 months ago). I took the following photos using my 24-105 f4 L IS attached to my 5D at night-time where the only lighting was a few powerful floodlights. I set the 5D on auto with AI focus and IS turned on. All were shot at ISO1600 and all were hand-held. The aim was not to capture anything of lasting beauty, I was just playing around:

Photo 1 taken @ 75mm 0.3s f4
Photo 2 taken @ 24mm 0.8s f4

As you can image the full 12.8MP 6GB files look a lot better than these uploads!
Perhaps these photos may help. I dont' regret going for the 24-105 f4 IS.

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I have the same quandary. I am not sure whether to go for the 24-105 or 24-70!! I recognise that the latter is faster and the thought of owning the fastest zoom that Canon makes is appealing, but my head tells me that if I really want DOF control and bokeh I should be using my primes anyway. With that said, the 24-105 seems to be the one for me as it has the length that I need for a WA and IS for those shaky moments when I can't hold her steady.

I really want the extra length as I have the 17-40 but find that I am using the 40 end most of the time so just can't capture the moments due to lack of range.

breakdown wrote in post #2714692
Personally, I would take IS over the f-stop because it is more useful for an all around lens I think. The only time I really need to freeze motion is when I'm taking portraits and, in that case, I usually use f/5.6 or f/8.

it's not just about freezing motion -- the extra stop gives you greater control over DOF and imo the 24-70L has slightly better IQ and bokeh.

if i were as happy with the IQ i would own the 24-105L.

ed rader