Tamron SP 2X Tele-Converter is compatible with most Adaptall-2 lenses. The 6 element, 5 group optical design is housed in a moderately long barrel which is about twice the length of a conventional 4 element converter. The flat field optical design minimizes off axis, spherical and chromatic aberrations. This tele-converter is designed for lenses with a focal length of 90mm and longer. This converter can be used with many Tamron wide to tele zoom lenses for doubling macro magnification.