A teleconverter sits between the camera body and lens essentially acting as a magnifying glass. They are used to increase the focal length of a lens but at a cost. Usually sharpness and lens speed. Sigma managed to avoid the sharpness issues with its TC-1401 1.4x and TC-2001 2x teleconverters that are currently available for Sigma A, Nikon F, and Canon EF. The company aims to continue the tradition with two new teleconverters for L-mount. 

The Sigma TC-1411 and TC-2011 are designed for Sigma mirrorless lenses and are to be mounted between the lens and the camera body. Like their counterparts, the TC-1411 magnifies the focal length of the camera by 1.4x, and the TC-2011 by 2x. However, optically, they are different. The TC-1411 is designed with 7 elements in 4 groups and the TC-2011 8 elements in 4 groups. 

The change in optics are said to provide "superior optical performance of the Sigma Contemporary, Art and Sports lines of lenses" and "upholds the image quality of the original lens to the utmost, while extending the focal length." What Sigma is saying here is that shooters shouldn't see a difference in the image quality between using a teleconverter and not using one. 

Sigma also notes the teleconverters have a dust- and splash-proof construction comparable to that of the Sports line and is able to withstand harsh conditions. The one issue, for now, is that the teleconverters are only compatible with a single lens, the newly announced 100-400mm F5-6.3 DG DN OS Contemporary. When paired with the 1.4x, it functions as a 140-560mm F7-9, and as a 200-800mm F10-12.6 at 2x. 

For now, Sigma users will have to wait until more lenses become compatible. The TC-1411 and TC-2011 teleconverters will be available on July 10, 2020, for $399.00 USD and $429.00 USD respectively.