Rob Galbraith DPI: New 500mm f/4, 600mm f/4 in development, says Canon

The new lenses target improved dust-proof and moisture-proof performance in the face of harsh shooting conditions to satisfy the demands of sports, news and nature photographers, as well as high-contrast, high-resolution imaging from the maximum aperture setting.

Link: Rob Galbraith DPI: New 500mm f/4, 600mm f/4 in development, says Canon