The Sigma 1.4X Teleconverter EX APO DG
The 1.4X Teleconverter EX APO DG from Sigma is a great option if you’re looking for a lightweight and compact teleconverter that delivers superior image quality. This is ideal for birders, sports shooters, and other long reach photo shoots.
This dedicated APO teleconverter is simply mounted between the lens and the camera body to increase focal length by the power of 1.4X. This increase occurs without any variation in minimum focusing distance.
So, your 300mm F2.8 becomes a 420mm F4 when the 1.4X teleconverter is added. It also offers new designed for digital multi layer coating that reduces flare and ghosting.