The Kenko TelePlus MC4 AF 2.0X DGX Teleconverter the MC4 features a 4-element, 4-group design with multi-coated lens elements, and fully automatic diaphragm coupling. With the Kenko TelePlus MC4 DGX your prime lens' depth of field is reduced by 1/2, but retains the prime minimum focusing distance. Using a 2x teleconverter with a 300mm lens will effectively increase the focal length to 600mm. A lens set to f/2.8 will now be f/5.6.
This is the magnifying factor of a lens. Macro lenses will often be described by their “magnification factor”. A lens with a 1:1 magnification factor produces a projected image on the sensor which is the same as the subject.
The individual pieces of glass that form the overall optical construction. Most lenses have between four and eleven elements to bend the light rays to ensure a perfectly formed image appears on the light sensitive surface, such as a film or CCD. The elements are arranged in groups and may be seen in specification sheets as, for example, 6 elements in 4 groups. That configuration may have two single elements and the other four grouped in pairs.