When would you use a 50mm F/1.4 lens and when would you use an 85mm F/1.8 lens? Are they both much the same? Are there situations where you would use one over the other? I'm relatively new to the world of digital photography - I own a Canon 30D SLR with three lenses - the 50mm, 85mm and a 17-85 zoom lens. I like taking photos of families and children - not that I have had much experience at this!