Voigtlander Turnit 3
Turnit 3 finder (339/50) from 1958.
Fits on the accessory shoe of interchangeable lens cameras.
Makes view easier with 35, 50 and 100 mm lenses due to a larger image without parallax (distance adjust by cursor).
Rotating 180° this attachment allows to easily change focals.
A mask allows to use it with a 50mm lens.
Top of the Turnit 3.
Underside of the Turnit 3.