The Tamron 2x Autofocus TeleConverter For Nikon DSLRs multiplies the focal length of the existing lens by 2x, and cuts back the amount of light by 2 f/stops.
Tamron tele-converters provide powerful and creative options for your telephoto photography. Simply fit a Tamron tele-converter between the lens and the camera body. This increases the focal length and gives you extended telephoto capabilities so you can take photos with greater magnification from the same camera position. Tamron's AF tele-converters are compatible with most AF (autofocus) and auto-exposure cameras. It is not recommended to attach a tele-converter to a lens where the maximum aperture is F3.5 or slower(for example a high power zoom lens)..You should check your lens instruction manual for information about compatibility of the tele-converter with each lens.
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.