Sigma redesigned the optical and structural design of this lens in order to achieve a relatively compact size, at 4.0" long, as well as a close minimum focusing distance of 13.8" for macro photography. Their Thermally Stable Composite (TSC) construction maintains the structure of the lens, with little variation despite changing temperatures. The lens also incorporates a brass-made bayonet mount, to further reinforce the lenses durability and resistance to wear and tear over time.