I'm familiar with the lens design limitations imposed by the flange-to-focal-plane distance. But what constraints are caused by the width of the lens mount (that is, the size of the hole in the camera body)? Clearly there's the fact that if your lens mount needs electrical contacts, they have to fit in somehow and you need to make arrangements for a diaphragm if the lens needs one. But what other limitations are imposed? For example, does it limit the maximum aperture of a lens?