Third party lenses for 5DIII

[Kayaker72]

GBC,

First off...congrats on your purchase. I bought the 5DIII in February and am about 2,000 shots into using it. I have to echo Patrick, for what you are describing, I would think that the 5DIII would excel. I would be very tempted to sell off the 7D and 17-55 lens to fund FF gear.

If you don't have much cash, the 24-105 "Kit" lens is typically available "in new condition" for ~$800 on ebay or craigslist, and I've seen them going for less. I know f/4 isn't as "fast" as an f/2.8 lens, but it has IS and will be faster for equivalent framing/DOF than the 17-55 f/2.8 on the 7D, which is equivalent to f/4.5. Plus you get the benefit of better ISO performance (I am using up to ISO 12,800). I have had good luck with the 24-105 f/4 on the 5DIII at high ISO in low light around the house.

Getting back to your original question, the third party lens I've heard very good things about the tamron 24-70 f/2.8 VC. A couple of links:

First, ISO 12233 crops from Bryan

A comparison of 24-70 lenses at lensrentals

A shootout comparison by the camera store

For the money, a good option. But it seems that the canon 24-70 f/2.8 II is the king, if you can afford it.

A quick summary of options (in order of increasing price):
1) Buy a "like new" 24-105 f/4 "used" for $600-$800
2) Buy a couple of standard primes such as the 50 f/1.4, 85 f/1.8, etc
3) Buy the Tamron 24-70 f/2.8 VC
4) Buy the Canon 24-70 f/2.8 II