It is natural for the image quality to deteriorate when using a teleconverter since the lens becomes darker due to aperture loss: one F-stop (with 1.4X) or two F-stop (with 2X).</br>Depending on the shooting conditions, the Auto Focus may hunt. In that case, please use MF (manual) mode.</br>This teleconverter is not designed for digital use. We do not guarantee its performance when used on Digital SLR cameras.</br>When using the teleconveter, it maybe difficult to achieve focus using AF because the depth of field becomes shallow. If this occurs, focus manually.For use with Canon SLR cameras</br>If used with a variable F-number zoom lens (e.g. 2.8-3.5), AF may not operate at the telephoto side. If this occurs, focus manually</br></br>Product Description</br></br>A Teleconverter is a great way to extend the focal length of your lens. This Teleconverter will extend the focal length of your lens by 1.4x giving more magnification. The Tamron Pro series Teleconverter offer superior optical construction for improved image quality.</br><br/>http://www.amazon.com/gp/product/B0007YZLJ4