Pro's usually always have good low F, fixed focus lens and shoot indoors without a flash - less red eye and less invasive than a flash. You cannot zoom to frame but the the fixed focus lens will give sharper images than a zoom (which by design loses some sharpness to have zoom flexibility)
They crop and expand image by software - on the camera or PC. The more you pay the better the lens and a fixed focus lens is no exception. Borrow one if you can and try it out. On a DX DSLR a 50mm fixed focal length length is equivalent to about 70-80 mm a great portrait lens.
