sentences:  Each manufacturer has developed their own system, and build camera bodies and lenses that only work with their own lens mount, with the Four Thirds System being a partial exception.This was different before 1970 when most of the manufacturers use either M42 or M39 lenses, most of which can still be used depending on the particular adapter you can find.This does not necessarily mean that one is limited to only mounting, for example, Pentax lenses on a Pentax camera body.