Canon Extender EF 2x III

The Extender EF 2x III mounts between a compatible Canon EF lens and body to double the lens focal length, turning a telephoto into a much longer reach for wildlife, sports, and aviation work. Its 9-element optical formula uses Canon's Super Spectra coating to control ghosting and flare, and a built-in processor passes full electronic communication for autofocus and metering between camera and lens.

It works only with select fixed focal length L-series lenses 135mm and longer, along with the EF 70-200mm f/2.8L, EF 70-200mm f/2.8L IS, EF 70-200mm f/4L, and EF 100-400mm f/4.5-5.6L. Dust- and moisture-resistant construction with front and rear anti-smear coatings suits it to outdoor use. Doubling the focal length reduces the effective aperture by two stops. Canon part number 4410B002.