Westside Guy is right about the size and weight. Unfortunately, that's photography for you. You need to pay a lot more, and carry a lot more weight, just to get a slightly better performance, slightly more reach, etc.
To be fair though, I don't find the 70-200 mm heavy. It's not light, but I'm a healthy, male, 27 year old uni student who isn't out of shape. I can hold that lens for ages.
Yes, and the 70-200 is about $1600? The 80-200 is about $900? Of course they look (and work) great; They're pro lenses!
Sure; you get "4x less light" for the same shutter speed, however:
1) Every time you want to go wide you're swapping glass. PITA!!
2) You need to pay for the sherpa to haul them around for you.
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3) Did I mention they are expensive?
1) He's going to shoot concerts for a magazine. A 70-200 mm focal length is a good range, although something that can do 35-50 mm would also be good if he's standing in front of the stage. This is important because the venues he'll be shooting at are likely small to mid-sized. Actually, a 105 mm f/2 would be excellent as well for shots that are somewhat far away.
2. Swapping lenses isn't a big deal. A band's appearance doesn't really change much between songs.
3. Yes, the Nikon 80-200 mm is expensive.....around $850-900.
Sigma 70-200 mm is around $850-900.
Sigma 50-150 mm is around $650.
The Nikon 18-200 mm is also expensive, with a pricetag of around $750. Sound much cheaper to you?
Like you said, the Nikon 80-200 mm works great, as it is "pro glass." Why pay almost the same amount for something that won't be good enough for the job? If it doesn't do the job, then he just threw away money. Don't get me wrong. I know some people aren't fans of the 18-200 mm, but I am a fan. However, I wouldn't recommend it for what he shoots. I'd recommend it for general photography, maybe even an outdoor wedding. However, for bands?
The Sigma 50-150 mm f/2.8 may be even better than the 70-200 mm f/2.8 for shooting bands because it goes as "wide" as 50 mm. That's good. The 70-200 mm is needed if you're far away, but that usually happens at large venues for large bands (that his small magazine will probably not attend for the foreseeable future). At that point, the magazine can probably afford to buy him a 70-200 mm f/2.8 lens if he needs a bit more reach.
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