The Opteka 2x High Definition
Tele-Converter is for use with T-Mount manual focus lenses. It will multiply the
focal length of your existing lens by 2x, and will cut back the amount of light
by two f/stops.
For example, using a 2x tele-converter with a 500mm lens will effectively
increase the focal length to 1000mm. A lens set to f/2.8 will now be f/5.6.