Vivitar 2X4P 2x (4 Elements) Tele Converter for Pentax

The Vivitar 2x 4-Elements Teleconverter for Pentax cameras is a precision optical component designed to expand your photographic capabilities. This premium quality 2x teleconverter effectively doubles the focal length of the lens it's used with and maintains the resolution and contrast of any fine optic. The 2x teleconverter extender will multiply the focal length of the existing lens by 2x and will cut back the amount of light by 2 f/stops. For example using a 2x teleconverter with a 300mm lens will effectively increase the focal length to 600mm. A lens set to f/2.8 will now be f/5.6.