You really need to be looking out for anything with Vivitar on it. If memory serves me correct, Vivitar use glass made by Hoya along with the likes of Nikon, Canon and Pentax. Hoya are one of the Worlds biggest producers of optical glass and provide many top lens manufacturers with glass. Way back when, Vivitar used Hoya glass and had quite a reputation for making tele converters but as has already been stated, you need an M42 mount. You will very definitely lose some image quality though as well as light.