The Dallmeyer 20 Inch f/5.6 Telephoto is a long-focus telephoto lens from the British optical maker J.H. Dallmeyer, designed for large-format plate cameras where a narrow angle of view and substantial reach were required. Lenses of this length and aperture were typically used for portraiture at distance, naturalist photography and reportage on plate cameras during the late brass-and-bellows era.

Auction evidence for this exact reference is thin: a single UK saleroom result from September 2024 saw one sell for £50 at hammer, which is the wholesale level fetched at auction before buyer's premium and excludes seller's commission. With only one data point on file in 2026, that figure should be read as indicative rather than a reliable guide to what a clean example is worth today, and condition, completeness of the iris and the presence of the original flange will move the price materially.