After the conflict with Voigtländer, Petzval started a cooperation with Dietzler, an optician from Vienna. With him he built the landscape lens on basis of the Petzval portrait lens. Dietzler presented this lens in 1857, called "Orthoskop". This lens was less luminous than the Petzval portrait lens (1:3,7). According to Eder "less luminous but a wider sharp image field". When Voigtländer became aware of that he also built this lens with the help of the original construction papers by Petzval and he called it "Orthoskop". Up in auction a very rare lens, it's a Orthoskop Voigtlander & Sohn in Wien u. Braunschnveig serial 15961. After the photo you can see the model and measure in the attached table of the great book of Corrado D'Agostini "Voigtländer Petzval Dietzler Busch Steinheil Zeiss Photography lenses in 19th century Germany and Austria "to better understand what model and focal length it is. I think it is an N3 model so a focal length 611mm. This Orthoskop is in great condition, the glasses of the lens are clean and clear with no haze, no fungus, no scratches, no detachmet between the lenses. The lens measures 9cm long with hood, 78mm diameter of the front lens, 52mm diameter of the rear lens and weight is very heavy kg. 1,150. The optics is complete, it has its own ring to fix it to the camera, 4 apertures and the ring that holds the apertures behind the optics. In the first photo I put a 35mm film to better understand the size of the lens. Perfect addition to your collection!