a unique diffraction optics (DO) optical design allowing a much more compact lens but characteristic DO aberrations
specs
400mm f/4
image stabiliser allows hand held shots to 1/25th sec with some success
USM AF
internal focus
52mm rear drop in filters
9 blades
18 elements in 12 groups
weathersealed
close focus 3.3m
Lens hood: ET-120 (WII)
1.4x and 2x teleconverters can both be used with this lens to add more flexibility, although using a 2x converter will result in a slow maximum aperture of f/8 with this lens, which may also cause autofocus issues on some Canon camera bodies
233mm long
2.1kg
~$A7500 for version I and ~$A9000 for version II (the f/2.8 lens is ~$A12000)