The Kenko TelePlus MC4 AF 2.0X DGX Teleconverter (also known as a tele-extender) gives you the dramatic effect of doubling the focal length of your lens by 2x, and will cut back the amount of light by 4x (2 f/stops). 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.
The MC4 AF 2.0X DGX converter has genuine Gated Array IC (Integrated Circuitry). This means that not only the converter's own unique data but all data sent from the camera body provides full exposure metering and linkage for electronic flash photography.
Teleconverters are not recommended for lenses wider than 50mm, e.g. 28-105mm. However, full AF operation is only possible with lenses with open aperture of f/2.8 or brighter. Please be aware that AF will work properly only if there is enough light and contrast on the subject to activate the camera's AF sensors. Manual focusing is recommended when using lenses with smaller open f-stop value than those given above.