You can sometimes use old glass, but there are a lot of downsides. A lot of modern cameras put image stabilization in the lens. Old lenses can't autofocus, and

You can sometimes use old glass, but there are a lot of downsides. A lot of modern cameras put image stabilization in the lens. Old lenses can't autofocus, and that is crippling on some cameras. Also some meters and sensors don't necessarily work with the old lenses.