The 1.4 EX is placed between the lens and the camera, and it allows the photographer to use the 70-200mm f/2.8 lens as a 98-280m f/4 lens, and the 300mm f/2.8 lens as a 420mm f/4 lens; the high optical performance is maintained and the AF speed is not affected.
Lens construction: 5 elements in 3 groups
Focal length: 1.4x that of a master lens
Aperture coupling range: F2.8 - F32
Reproduction ratio: 1.4x that of a master lens
Dimensions: 68.5 X 19.5mm (2.7in. X 0.75in.)
Weight: 143g (5oz.)