The Kenko TelePlus MC4 AF 2.0X DGX Teleconverter (also knownas a tele-extender) gives you the dramatic effect of doubling the focallength 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 withmulti-coated lens elements, and fully automatic diaphragm coupling. Withthe Kenko TelePlus MC4 DGX your prime lens' depth of field is reducedby 1/2, but retains the prime minimum focusing distance. Using a 2xteleconverter with a 300mm lens will effectively increase the focallength to 600mm. A lens set to f/2.8 will now be f/5.6.The MC4 AF2.0X DGX converter has genuine Gated Array IC (Integrated Circuitry).This means that not only the converter's own unique data but all datasent from the camera body provides full exposure metering and linkagefor electronic flash photography.Teleconverters are notrecommended for lenses wider than 50mm, e.g. 28-105mm. However, full AFoperation is only possible with lenses with open aperture of f/2.8 orbrighter. Please be aware that AF will work properly only if there isenough light and contrast on the subject to activate the camera's AFsensors. Manual focusing is recommended when using lenses with smalleropen f-stop value than those given above.Note! NOT for use with Canon EOS EF-S lenses â€¢ The DGX TelePlus converters have updated circuitry to record exif data more accurately. In the exif exposure data (meta-data recorded with a digital picture) DGX converters record the equivalent aperture and focal length of the lens setting plus teleconverter. Optically and mechanically they are identical to the prior high-quality DG series converters.