Hello!
Has anybody know the French lens maker named DY? The lens is engraved "Brevet d Invention DY Paris". This is a convertible Petzval-type lens, each element mounted by bayonet and the front achromatic doublet can be used as a landscape lens. Rack and pinion mechanism is present, so it's an earliest Petzval lens, as I can estimate. The place for washer stops is present too. Estimated focal length is 220 mm and wide open approx. 4. Any information will be helpful, thanks.