A vintage brass lens using a Petzval formula in ‘very-good’ optical condition. There are no scratches on the lens surfaces and no fungus.
You will see that it still has its mounting flange which will make mounting it to a lens board a lot easier.
It is marked, "Rath Opt Jnd Anst Vorm Emil Busch Rathenow” on one side, and “Portrait Doppel Objectiv No.4 - Back Foc 7 ins” on the other side.
The back focus is marked as 7 inches (177mm). Because focal lengths are normally measured from the centre of the lens, for comparitive purposes, the focal length is closer to 230mm when I add the extra distance to the back of the lens to the Waterhouse slot. I calculate the maximum aperture to be f3.6 (this is a measured value, so should be considered to be appoximate only). It appears to cover a full-size plate when I project an image onto a white sheet of paper (there is bound to be some drop-off at the edges due to the nature of Petzval lenses).
The lens has a slot for Waterhouse stops, but no stops are included.
The lens (including hood) is approximately 16.7cm long and the hood is approximately 9.2cm in diameter. The flange is approximately 13.3cm in diameter. It weighs 1657g.