The Kenko 1.4x Teleplus Pro 300 DG converter has genuine Gate Array IC (Integrated Circuitry). It means that the converter's own unique circuitry maintains signal integrity between the digital or photo camera body and lens. These converters are designed to electronically operate the same way as an original manufacturer's converter. The 1.4x teleconverter (also known as a tele-extender) will multiply the focal length of the existing lens by 1.4x, and will cut back the amount of light by one f/stop. For example, using a 1.4x teleconverter with a 300mm lens will effectively increase the focal length to approximately 420mm. A lens set to f/2.8 will now be f/4. Teleconverters are best used with longer telephoto lenses and 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/4 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.Note: Not compatible with Canon EF-S lenses, e.g. 18-55mm, 17-85mm.