British inventor and manufacturer of lenses.

Showing an aptitude for science, Dallmeyer was apprenticed to an Osnabrück optician (optics), and in 1851 he went to London, where he obtained work with an optician and later with Andrew Ross, a lens and telescope manufacturer. After a year spent in a commercial post, he was reengaged by Ross as scientific adviser. He married Ross's second daughter, Hannah, and in 1859 inherited part of his employer's large fortune and the telescope-manufacturing portion of the business. Turning to the making of photographic lenses, he introduced improvements in both portrait and landscape lenses, in object glasses for the microscope, and in condensers for the optical lantern. He constructed several photoheliographs (telescopes adapted for photographing the Sun).

His son Thomas Rudolphus Dallmeyer (1859–1906) introduced telephoto lenses into ordinary practice (patented 1891) and wrote a standard book on the subject (Telephotography, 1899).