2.5/28mm lens RO61, OCT-18 Konvas mount
This high-quality lens was made in 1950's at KMZ (Krasnogorsk factory).
The lens is purposed for 35mm film movie cameras like Konvas, Kinor, Arri etc. Covered frame size is 16x22mm. Actual coverage is larger, but not enough to cover still image 35mm frame (24x36mm) - there are dark corners. Also, back focus is quite short, so it will not work with reflex cameras like Canon or Zenit. But should be fine for hybrid cameras.
The lens has so called OCT-18 mount (for turret Konvas cameras), but you may adapt it to other camera.
Max. diameter: 58 mm
Mount diameter: 47 mm
Length: 55 mm
Weight: 130 g
Mechanical condition is fine. Aperture control ring works well (T/3-22, click stops). Focus ring is smooth (1m - infinity scale).
Optical condition is fine as well. No fungus, no scratches. Just few cleaning marks and dust particles.