I'm still new to photography, but it seems almost like a rule that 50mm lenses are used for portraits. My only question is, is this 50mm equivalent, or a lens marked 50mm? The reason I'm asking is that walking around at home with my 18-70mm lens set at 50mm (plus 1.5x crop factor) seems a little too close to use in the confines of a house for small group shots. I'd like to get a really fast prime for indoor/no flash shots, and I'm thinking I might want something less than 50mm. What do you guys use? Thanks.