As a long time film photographer, I have been doing my best to educate myself on digital before I dump $$$$ on equipment. When I look down the barrel of a film lens, the glass takes up most of the diameter of the barrel. Lenses on dslr cameras in the Canon Rebel XS and Nikon D60 range spook me because there seems to be a much smaller lens sitting in the center of the big lens. Big Boys like the Nikon 300 have lenses like I am used to seeing in film cameras. What's the difference between the two styles of lenses?