Keep Sigma teleconverters in mind when selecting
lenses for your camera. 2X teleconverters are more popular and powerful. 1.4X teleconverters are more useful and often have less distortion too. 3X teleconverters are rarely used
anymore, as they have so much image degrading effect as to be worse than simply enlarging a smaller image. Teleconverters work much better on telephoto lenses (200mm and up) than on shorter
focal length lenses and typically work better on
prime lenses than on
With a 1.4X teleconverter, you lose a stop of light. So an 135 f/2.8 lens becomes the equivalent of a 190mm f/4. A 200mm f/4 becomes a 280mm f/5.6 equivalent. With a 2X teleconverter, your 135mm f/2.8 becomes 270mm f/5.6 and your 200mm f/4 is a rather slow 400mm f/8 equivalent. You can also convert your
50mm f/1.8 into a 100mm f/3.5 using a 2X.