I don't know what this lens is. H Dallmeyer London BB n°10117. It doesn't seem to be a genuine Dallmeyer lens. The barrel seems have been modified and cut for waterhouse slot.
It should be a taking lens from the 19th century, and used as enlarging lens or projection lens. The mounting flange is included and I can't unscrew it. Otherwise it's a petzval optical design lens, with cemented front achromat and separated by air rear achromat. Glasses are complete and in good condition.Brass barrel wears some marks and varnish loss. There is a waterhouse slot and a rack & pinion focusing system. A front inactinic screen (brown/red) is included. The image projected on 8x10 ground glass of my camera is bright and sharp (with vignetting and swirly bokeh). I guess this lens is able to take great pictures for large format photographers and wet plate enthusiasts. Check out my other antique lenses for sale. L'item "Dallmeyer BB petzval large format 240mm 5X7 6x8 brass lens wet plate" est en vente depuis le jeudi 20 juin 2019. Il est dans la catégorie "Photo, caméscopes\Photographie ancienne\Objectifs anciens".
Le vendeur est "75photographica" et est localisé à/en Paris, Ile-de-France. Cet article peut être livré partout dans le monde.