Placed between the camera body and lens, a teleconverter contains a set of optics that will effectively increase the focal length of any lens with which it is used. The Kenko TelePlus MC4 AF 2.0X DGX converter has the effect of multiplying the focal length of your lens by 2.0x, turning a 300mm lens into an equivalent 600mm lens. The MC4 AF 2.0X DGX converter has genuine Gate Array IC (Integrated Circuitry). It means the converter's unique circuitry maintains signal integrity between the camera body and lens.
The 4-element design is made with high quality multi-coated optical glass supplied by Hoya Corporation, the world's largest manufacturer of optical glass. Full AF operation with the TelePlus MC4 AF 2.0X is possible using camera lenses with open apertures of F2.8 or brighter. AF will work properly only if there is enough light and contrast on the subject to activate the camera's AF sensors. (Manual focusing may be necessary when using lenses with smaller open f-stop values than that given above.)
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.
Reviewed by 4 customers
Yes, it doubles your focal length. Yes, it's decently sharp. Too bad you have to shoot on f11 with a f5.6 lens, which eliminates fast shutter speeds, and causes blurry, shaky shots, especially without a VR lens or at longer focal lengths. It does a decent job with color/contrast, although it does lower them slightly, this can easily be corrected. Sharpness is actually pretty good if you somehow get a fast shutter speed out of it. The teleconverter, when attached, seems to have a tendency to throw off the camera's metering, and cause vastly overexposed shots at random times. It became very annoying and because of this and the constant need to manual focus, which simply does not work in wildlife photography, I returned it. Do not buy this Tele-Converter. You get what you pay for.
Less expensive & lighter weight than a big piece of glass.
First converter I have ever used. Although it doesn't work with the Sigma 70-200 f/2.8, in auto focus, it does a great job in manual focus. Images are sharp and saturated. I use it for wildlife and sports shooting. Even in MF, the sports shooting is easy and sharp.
Unfortunatly, the D90 can not fix the focus.