Sigma 2.0x EX DG APO Teleconverter Pentax Fit

The 2x EX DG is placed between the lens and the camera and allows the photographer to use the 70-200mm f/2.8 as a 140-400mm f/5.6 telephoto zoom lens, and the 300mm f/2.8 as a 600mm f/5.6 ultra telephoto lens; Its lens contruction has 6 elements in 5 groups; The focal length is twice that of a masters lens; The reproduction ratio is again twice that of a masters lens; The aperture coupling range is F2.8 - F32; Dimensions: 68.5 x 52mm (2.7in x 2.05in); Finally its weight comes to 234g (8.3oz.)