[Fire Me Boy!]

Originally Posted by kepp

My main use for it will be shooting inside - gymnastics events where lighting is usually decent, but not always. I was concerned with the f/4-5.6 value in regards to that. He claimed it would be fine because (his words) if you use a f value of 2.8, then usually only part of the person will be in focus and not the entire subject. But if I use 4 or over, the entire person would be in focus. I have no idea if that's true.

Also, its just a local shop and they don't have an online presence AFAIK.

He's basically right on the depth of field, but he's not really educated. The further away from the subject you are the more depth you have. For instance: if you're shooting at f/2.8 with a 100mm lens and your 10 feet away, you've only got about 4 inches of pure focus. But if you're 50 feet away, you've got a little over 8 feet. The higher the f-stop, the more wiggle room you have. At f/4 at 50 feet you have almost 12 feet of focus.

Here's the basics on depth of field, if you care to read up more: http://www.exposureguide.com/focusing-basics.htm

And here's a handy-dandy DOF calculator, if you're interested: http://www.dofmaster.com/dofjs.html

The issue with light (and just because you think it's fairly well lit doesn't mean your camera agrees) is you'll need to crank up the shutter speed to at least 1/250th of a second to even come close to stopping the action, and you'll be a lot better off if you can get it to 1/500th. In order to get that kind of shutter speed indoors, you'll need two of the following: good lighting, low f-stop, or high ISO.