Praktica 135mm f/2.8 M42

Standard telephoto. Constructed solidly. The focus ring on the small circulation causing problems collecting the focus. This model is marketed under various names. eg Luxon, Helios...
Check this link: http://www.vintagelensesforvideo.com/helios135mm/

Optics: ★☆☆☆☆

Dark.  Not sharp. A waste of time.

Ergonomics: ★★★★☆

Works just fine.

Build quality: ★★★★☆

A very good workmanship. Everything is working perfectly.

Market value / value of subjective: ★★☆☆☆

Less than $ 10 is a very good price.

Here are some sample pictures.

They were made with Sony Alpha 300.
Pictures were taken with aperture F/5.6 ISO-100
All photos without amendment in graphics programs.