The diaphragm is completely oil-free, the diaphragm works well.
Sample photos
taken with this lens on a Sony A6000.
Photos were taken from a distance of 2-2.1 meters (7 feet).
Photo 8 with aperture value 2.0Technical information:
Lens Mount: M42
Focal Length: 58mm
Aperture: 1: 2.0
Aperture range: 2.0-16
Aperture: 6 aperture blades, Manual
Focus range from 0.5m to 10m to infinity
The filter holder: M52x0.75