Getting the Canon 400 5.6L raised the quality expectation I had of camera lenses, immediately getting rid of the three I already had which now didn't seem up to the job. The choice was between this and the Canon 100-400mm and don't regret buying this as I've only once found I would have liked to...

VERY sharp; light; fast focus; use with converter; lightweight; quality build

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Canon classifies the Canon EF 400mm f/5.6L USM Lens as a "Super Telephoto" lens. It is super in image and build quality , but is not super in size . The 400 f/5.6 is relatively light in weight but very solidly built . It feels long and narrow in your hand - and feels even lighter than it is.