I shoot a lot of events and use a 5D and 24-70 mostly. I started with a 30D and 17-40 and found the going hard. IS doesnt really come in to it at gigs as it may stop your camera shake, but wont stop your subject from motion blurring. IS is more handy at the longer focal lengths.

To be honest, you need as much help as you can get in the low light. Therefore good low light body such as d700, d3, 5D, 1D are really the go if you want to be selling shots. You might get away with a 50D or d300. Primes are great for low light but can be restrictive when you have limited vantage points. You dont want to be swapping lenses amongst the crowd. f2.8 zooms are the go, dont settle for a f4. f2.8 is twice the amount of light as f4.

All this is irrelevant anyway if you dont understand the fundamentals of photography. Its an expensive hobby so you should try and limit your upgrades as much as possible.

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betty banger