Although the aperture becomes one f-stop higher when mounted, the teleconverter features an excellent optical design with a construction of 7 elements in 3 groups to maintain the optical performance of the original lens. Also, thanks to the unified design when mounted to a compatible lens*, the teleconverter is weather and dust-resistant and operates at temperatures as low as -10°C. This makes it possible to be used with confidence outdoors when used with the weather and dust-resistant camera body and lens.