The Canon EF 400mm f/5.6 L Ultrasonic is a super-telephoto prime lens for the Canon EF autofocus mount, built within Canon's professional L-series and driven by an ultrasonic (USM) autofocus motor. Its long reach and fixed f/5.6 maximum aperture make it a working tool for wildlife, sports, and aviation photographers who need a relatively light, fast-focusing 400mm prime.

UK auction data for this lens is thin: the only verified hammer result on file is £320 in April 2023, achieved at saleroom level (excluding buyer's and seller's premiums). With a single data point, that figure is best read as an indicative wholesale value rather than a reliable median, and buyers asking what an EF 400mm f/5.6 L is worth in 2026 should weigh condition, accessories, and the absence of image stabilisation when judging price.