The Nikon Telekonverter 1.4x III extends the focal length of an optic by a factor of 1.4, and the open aperture also changes by this factor. Makes a 200mm/ 2.8 to a 280mm 3.2 lens. A good and favourable alternative to expensive and heavy telephoto lenses. The Converter is not compatible with all Lenses. here is a list of the ones which can be used: AF-S VR Micro-NIKKOR 105 mm 1:2,8G IF ED¹, AF-S NIKKOR 200 mm 1:2G ED VRII, AF-S VR NIKKOR 200 mm 1:2G IF-ED, AF-S NIKKOR 300 mm 1:2,8G ED VR II, AF-S VR NIKKOR 300 mm 1:2,8G IF-ED, AF-S NIKKOR 400 mm 1:2,8E FL ED VR, AF-S NIKKOR 400 mm 1:2,8G ED VR, AF-S NIKKOR 500 mm 1:4G ED VR, AF-S NIKKOR 600 mm 1:4G ED VR, AF-S NIKKOR 70–200 mm 1:2,8G ED VR II, AF-S VR Zoom-NIKKOR 70–200 mm 1:2,8G IF-ED, AF-S NIKKOR 70–200 mm 1:4G ED VR, AF-S NIKKOR 200–400 mm 1:4G ED VR II, AF-S VR Zoom-NIKKOR 200–400 mm 1:4G IF-ED, AF-S NIKKOR 800 mm 1:5,6E FL ED VR² and AF-S NIKKOR 80–400 mm 1:4,5–5,6G ED VR².