Could someone bring me up to speed regarding the 45mm f2.8p lens? I am new to this stuff, and have been doing a fair bit of research, but I am sure I am missing something here. This lens has an amazingly low weight and size, and still offers a half decent maximum aperture at 2.8. Can someone perhaps do a comparison with a 50mm 1.4. I realize the the 50mm 1.4 will do so much more in low light situations, but what else should I be aware of?