Tamron optical/mechanical key for Tamron 180mm f3.5 Lens is as "IF","LD","DI".
The IF implies that lens incorporates Internal Focusing system, where the lens
components moves inside the lens body, with soft, quiet and fast effect. Tamron
180mm has effect AF to MF switch converter by mean of one touch focus ring. The
lens has Low Dispersion glass elements in the optical system for correction of
aberrations. It comes from the DI-"Digitally Integrated" series lenses, that
works ideally with digital single lens reflex cameras. Other details of the lens
are given below.