The mounting system varies from camera, to camera. Some are screw mount, while others have different bayonet mounts (twist to lick) and are not interchangable. Minolta Lenses are specific to Minolta cameras, while Vivitar produces after-market lenses made with various mounts. There will also be some older lenses that will not work on new digital cameras. And some (within the same brand such as Canon) may fit, but lose functions such as auto focus.