Leitz Torpedo viewfinder.
VISAX
Looking at the profile view of the VISAX the origin of the nickname Torpedo finder is apparent.
This early viewfinder gives a fairly bright and large image that is laterally reversed, so it takes a little getting used to, much like the image in a TLR or medium format camera.
The VISAX is one of the rarer torpedo style viewfinders that accommodates framelines for 3,5cm (35mm), 5cm (50mm) and 9cm (90mm). The framelines are not the bright line style as in later finders but are simply black lines, the 35mm area is marked by the extremities of the viewing area. Interestingly parallax correction is only available for the 90mm framelines and appears as a dotted line.
Rear of the viewfinder showing the eyepiece with knurled section. When shooting with the camera vertically you have to rotate the rear knob, if you do not do this the image will appear upside down in the view finder.
VISAX mounted on a Leica II (D)