I have a documentary project that will require some portraiture. I'm generally a landscape and architectural photographer and only shoot people and portraits occasionally and with casual intent. These will be more formal, made using natural light, probably with a 35mm Nikon, and hopefully showing some of the environment as well. What lens should I use? Most of this project was shot using a 24mm lens plus an 85mm as well. Can anyone give me advice or suggest a book that might help with these kinds of pictures? Thanks.