What Is a Secondary Lens Mount?
A lens Mount is basically an interface which facilitates the joining of a lens with the camera body or another lens. When the lens mount is structured mainly within the body of the camera and is used to connect a lens, it is called the primary lens mount. The secondary lens mount is used to connect another lens to the primary lens, and it can be between the body of the camera and primary lens or between the primary and secondary lens.
The Role of a Secondary Lens Mount
The secondary lens mount is mainly used to connect the secondary lens. The secondary lens is usually a lens of multi-element nature and will not have control for aperture or focus. When teleconverters are used between the body of the camera and primary lens, then they use the primary mount and not a secondary lens mount. Some digital cameras that have a fixed zoom lens provide an attachment called a Conversion Tube, which provides a screw thread for a filter or other accessory.