If you love a subject, I'm not sure how you are going to stop at one or two books on it... so I've never understood the question myself. I'll list some books you should read for starters:
Cinematography (Third Edition) -- the one I co-wrote -- it's really about shooting 16mm from start to finish, including post, sound, lighting, etc.
Film Lighting - Malkiewicz
Cinematography -- Blain Brown (this one is more expansive on the subject, including aesthetics, etc.)
The Filmmakers Handbook (also expansive on the topic of filmmaking)
Classic textbooks (though dated somewhat):
5 C's of Cinematography (basic principles)
Painting with Light - John Alton (historically interesting on old-fashioned lighting principles)
Film Style & Technology -- Barry Salt (history of film style and how film technology influenced it)
Lenny Lipton's books on Independent Filmmaking and Super-8
Interviews with Cinematographers books:
Masters of Light
Cinematography Screencraft
New Cinematographers
