wow, thanks guys for all your replies, it really made me rethink my strategy.
@Kendra-Paige: thanks for the link, that is exactly what I am looking for.
@FallisPhoto: you are right, i was leaving out a lot of the variables.
The camera would be a canon EOS 600D. Right now he has a Canon Powershot SX30 and is looking to upgrade. So i recommended to him that this would be a step up. what do you guys think? good idea or not?
I suggested this one cause I liked the fact that it can shoot HD video at high frame rate, suppose to be easy to use (but if not, dad always did like a challenge), rotating LCD (which my camera doens't have...), 18 megapixels, wide range of ISOs (ok, maybe dad doesn't need an ISO of 6400...),
As for the environment: classroom would be steep, with the back higher than the front, and it would be from the back of the classroom, because doing it at the middle or the front can be disruptive to the class and dad doesn't like that. lighting would be florescent light, subject would most certainly be people, no PPTs. There is no point (for my dad anyway) to shoot someone else's PPT, he can usually just ask.
If he's going to be shooting by florescent light, he is going to need a camera that performs well in low light. He'll be shooting at 1/125th second or slower, no faster than that, because florescent light flickers. We can't see it because our brains trick us into believing the light is steady, but it isn't and a camera can see it. Flourescent light gets brighter and dimmer in cycles of 1/120th of a second. The difference is significant enough that it can effect exposure at high shutter speeds. I've found that 1/60th second is best for uniform exposures with florescent lighting. You want to keep the ISO pretty low with that many MP, to keep the noise down to manageable levels, so assuming he is not going to be shooting from a tripod, he'll want a fairly fast lens.
Is the high frame rate really going to be important, given the type of photography he is doing? There are other types of photography wherein it would be very important, but is he doing any of those types of photography?
If the classroom is steep, he's probably not going to have to hold the camera over his head every time a student stands up, so the rotating LCD probably isn't important -- at least not for the stated purpose. It could be important in other venues though.
One other thing: It often is not a good dea to get the camera a manufacturer makes that has the most megapixels. Those are usually made in response to the demand by dumb people who base their decision soley on that one criteria. Those cameras are usually not very sharp and are noisy as hell in low light. The exceptions to those are the cameras that use noise reduction software that is built into them, and those can have other issues. You are usually better off picking a camera with a medium or high medium number of megapixels. I remember when Canon made a whole bunch of 8mp cameras, a few 10mp cameras and one 12mp camera. Everyone who bought one wanted to know how come their expensive 12mp camera took photos that were not as sharp and clean as those from the 8 and 10mp cameras. It was because they were pushing the envelope of the technology of the time and they were pushing it too far. From time to time some manufacturers still do that. Kodak's infamous 14 mp camera, manufacturered back when everyone else was making 5 and 6 mp cameras, was an excellent example of this. It sucked ass horribly, in every way possible.
Another thing: You've probably made a false assumption. You are assuming that he will always be sitting in the back. He may not only be shooting from the farthest row; he might be shooting handheld from the nearer rows and/or from the middle too. This means that, if he wants to do it all with one lens, it is going to have to be a zoom lens. A 70-200mm lens (or something close to that) would cover it all, I'd think. A 70-300 might be a bit much, and the rule of thumb for zooms is that the bigger the range of zoom, the less sharp the lens is likely to be.
There is no way, given your situation, to figure out what would be ideal because you are leaving out way too many variables. A few examples: How big is the subject? How much of the surrounding environment do you need to capture (i.e. is there a chalkboard, charts or a powerpoint device)? What is the lighting like (will there be a slide presentation)? What kind of camera will the lens be attached to and what is its format? Is there a fixed, fairly precise distance?
Depends. Are you talking about taking a group photo, a full-length photo or a head-and-shoulders photo? Also, a room can be rectangular or square, and it can be stepped or flat, so what is the approximate distance in feet, yards or meters?
I doubt 70mm will be enough, depending on your budget id suggest either a 70-200 F2.8 (expensive but great in low light) or a 70-200 F4 (less expensive, not as good in low light), or 70-300 (cheap but not struggles in low light)