The Dallmeyer 51mm f/1 Oscilac 4:1 is a specialist ultra-fast lens from the long-established London optical maker J.H. Dallmeyer. With a maximum aperture of f/1 and a stated 4:1 reproduction ratio, it was built for oscilloscope-trace recording and similar scientific imaging tasks rather than general photography.

At recent UK auction, hammer prices for this Oscilac have ranged from £250 to £650, with the two recorded results in 2023 giving a midpoint near £450 — wholesale saleroom levels achieved before buyer's premium. Specialist scientific optics like this attract a narrow pool of bidders, so today in 2026 what one sells for can swing widely depending on cosmetic condition and whether the original mounting hardware is present.