I've decided I want to upgrade to a better lens, but I'm really torn between the Canon EF 70-200mm f/2.8L IS II USM and the EF 24-70mm f/2.8L II USM. I like to take convention photos, where space is tight and lighting isn't always the best (the lens I'm using now isn't very good with the dim lighting or space issues), so I need something that can handle both these. But I'm really drawn towards something that takes really amazing beauty shots. Advice?
closed as primarily opinion-based by Michael C, NickM, Hugo, Philip Kendall, inkista Oct 14 '15 at 17:32
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These lenses are both very good but for tight spaces, you will want a wide-angle rather than telephoto, so between those two, the 24-70mm F/2.8L will be more suitable.
Another point is that when lighting is low, you need slower shutter-speeds. Longer lenses though need faster shutter-speeds to be sharp, so again this favors the 24-70mm over the 70-200mm.
I have both of these lenses and they both work well for what you are talking about. They still require a higher ISO than a fast prime would, however they are very solid and very sharp. Of the two, the 24-70 is slightly sharper than the 70-200. I actually was a bit disappointed with the 70-200 when I first got it because of how blown away I was by the 24-70, but I later realized that wasn't really fair as I got used to both of them.
Ultimately, the decision between the two is much more artistic than technical. The field of view is going to be different between the two. You will need to be further away from things to use the 70-200 vs the 24-70. That will also impact the depth of images and distances involved in depth of field. There will be some shots you can't get with either, so pick based on shooting distance and angle of view that you want to be able to cover the best.
You may also need to consider a prime, since you can get at least a full stop faster, allowing for a better picture but sacrificing zoom utility. Also, a prime will be lighter, so you can simply see more things and get more photos taken.
The 70-200 F2.8 IS paired with a 60D is just about the limit I can handle at a safari. A full frame body will be heavier still and it won't be fun to lug that around.