So, I'm looking for a good lens to use for some private eye work for my company. Idealy I'm looking for something that can be used to get close to a subject but is sort of small and compact, something that can be handled inside a small car interior. I think a zoom is pretty darn important since I'll be stuck in one place for hours at a time, I was thinking Canon 100-400L but the 5.6 seems a little slow, although I've heard the IS is fantastic on that lens. I'm not looking for anything that's a sharpness king, but something that will still take good photos and can get into the 400+ range. How's the Sigma 150-500 still really slow, but it seems like it might work well, possibly with a tripod setup in the car. Any ideas?