Pentacon's auto 135mm f/2.8 — a common East German M42 portrait telephoto with round bokeh.
The Pentacon auto 135mm f/2.8 is an East German short-telephoto prime made in M42 mount from the early 1970s by the Pentacon combine in Dresden. Descended from the Meyer-Optik Orestor 135mm design, it was one of the most common vintage 135mm telephotos and a staple portrait lens of the M42 era.
This is a manual-focus M42 screw-mount lens with a 135mm focal length and a maximum aperture of f/2.8, with an automatic diaphragm marked by the auto designation. Focus and aperture are set by hand on the barrel, and these lenses are known for a many-bladed aperture giving round openings. It is an all-metal short telephoto. Exact element figures are not asserted here beyond the verified focal length and aperture.
At 135mm f/2.8 the lens is a classic portrait and short-telephoto tool, giving compressed perspective and good subject isolation. Its fifteen-bladed aperture on many copies produces very round out-of-focus highlights, and it is popular among vintage users for pleasant, characterful bokeh that flatters portraits and renders distant detail well.
Used copies are very common and inexpensive, among the easiest vintage telephotos to find. Inspect for haze, fungus and cleaning marks, confirm the many aperture blades are clean and oil-free, and check the aperture-ring and focus feel. Verify the M42 mount. An M42 adapter makes it a cheap, characterful manual portrait telephoto on mirrorless.