The Sigma TC-2001 2.0× Teleconverter increases the focal range of your lens. It is designed for Sigma SA-mount lenses. You can use the autofocus and autoexposure functions with this teleconverter placed between the lens and camera. The teleconverter has 10 optical elements in 5 groups. Two Special Low Dispersion elements are included in the teleconverter design to reduce chromatic aberrations. With this teleconverter, you get 2-times zoomed view of the lens's focal length with a light loss of 2 stops. The teleconverter can withstand water splashes and dust to ensure long-lasting operation.