The Carl Zeiss Jena Tessar 50 mm f/ 2.8 semi-auto is a normal prime lens (with "raised bumps" ring) for 35mm SLR cameras with the M42 screw mount.
The lens is remarkable for its semi-automatic aperture control. The operation principle is rather simple: the lens diaphragm has to be cocked open with a lever to full aperture prior to each photograph Upon pressing the plunger on the lens, the lens stops down first and then the shutter is fired. To ensure steady automatic operations the number of aperture blades has been reduced to 8.
Due to this peculiar aperture control the lens is not very popular and, consequently, is not very expensive in the secondary market. As it has a high aligner ring, the lens can be redesigned to fit Nikon cameras. Besides, automatic cocking can be easily switched off to use the lens on modern DSLR cameras.
As is the case with all CZJ Tessar lenses, it produces a branded bokeh and pictures with warm and saturated colors.
| Focal Length: 50mm |
| Field of View: 47° (diagonally) |
| Aperture Range: 2.8 – 22 |
| Number of Aperture Blades: 5 (rounded) |
| Min Focus Distance: 0.35 m |
| Filter Size: 49mm |
| Lens Mount: Contax RF / M42 / BM / EXA / EXAKTA / Altix-N / PENTAX / PRAKTINA |
| Weight: 170 g |
| Length: 37mm |
| Elements/Group: 4/3 (Tessar) |
