Bermpohl Naturfarben Kamera
c. 1930
Bermpohl & Co.
Berlin
Germany
Lens:
f4, 30 cm Double Plasmat, iris diaphragm to f32. Serial no. 583442 .Shutter:
Compound, speeds 1 - 1/50, B, T.Construction:
Polished teak body, deal internal fittings, brown leather bellows.Format:
Three, 13 x 18 cm plates.Focusing:
Bellows to 50".Attributes:
Three plates are simultaneously exposed behind Red, Green and Blue filters.Serial Number:
529 .Notes:
The filters carry the serial number of the camera.With:
Focusing screen. Two wooden blanking plates. Nitraphotlicht Tageslicht Grun filter 42/A. Nitraphotlicht Rot filter 43/A. Nitraphotlicht Blau filter 41/A.The Bermpohl is a one-shot camera for colour separation negatives. Three negatives are produced for red, green and blue images with the appropriate colour filter positioned in front of each negative. The light is divided behind the lens by two semi-silvered mirrors. To prevent double images from being formed by reflection from the back of the mirror it is coated, on the back, with the minus colour for the negative to which it is directed.
There were many designs for similar cameras using two, or sometimes three, mirrors to separate the light. The differences centred around the position and angle of the mirrors and how to overcome the two problems of refraction caused by the mirror and equalising the optical path. Light passing through the semi-silvered mirror is refracted, as the light strikes the mirror at an angle the image will be in a different plane and at a slight angle to its position if there were no refraction. Suggestions to overcome this problem included using wedge-shaped mirrors or placing another clear glass at an opposite angle in the image path (this was suggested in Pfenninger's patent 25907 of 1906). Dawson (patent 24538/12) suggested skewing the sensitive plate by means of adjusting screws near the plate holder. This is also proposed in Wilhelm Bermpohl's patent for this camera (US patent 1951896, filed March 1930, granted 1934), the patent shows two of the image planes skewed slightly. The second problem is to ensure that the optical paths of the three images are the same, in the Bermpohl clear glass plates are positioned in front of the red and blue images, the green image passes through the 'red' and 'blue' mirrors. The filters are of different thicknesses.
The 
camera was popular in studios, especially for advertising work. The negatives would have been used in photomechanical processes or for producing photographic prints (e.g. carbon, carbro, etc.).
The Bermpohl was produced in three sizes: 9 x 12 cm, 13 x 18 cm and 18 x 24 cm. Different filter sets were available to match the colour temperature of the light.