LOMO OKS5-18-1 (2.5/18mm)

This lens was designed at NPO "EKRAN". It has extended Back Focal Length so it can be mounted on 35mm film movie cameras with 19mm distance between mirror shutter and film plane.

The lens provides acceptable image quality comparable to Cine Prominar 2/20 mm, and superior to Super Baltar 2/20 mm.

I had ОКС5-18-1 lenses in different mounts (OCT-19, OCT-19 and other).

Specifications of the optical block OKS5-18-1

The lens has only 8 aperture blades, so octangular shape of the aperture opening is clearly visible.

Optical block has no aperture values marks. Also, there are no click stops. Effective relative aperture may vary a little (I saw T/3.1, T/3.2, and T/3.3 samples).
 

Manufacturer
NPO "EKRAN"
Lens system

-
Focal length
f'18.3 mm
Angle of view2ω'74°08'
Effective relative aperturef:nэ1:3.2
Lens length
Σd77.2 mm
Front focal lengthS-
Back focal lengthS'33.6 mm
Flange focal distanceZ
-
Block length
B78.4 mm
Block max. diameter
D62.5 mm
Rear diameter
D'33 mm
Front element diameter
d152.5 mm
Rear element diameter
d2
20.0 mm
Mount thread

SpM36x0.75 cl 2a
Distance from rear end of the housing
to the focal plane
l
-
Aperture blades quantity

8
Frame size

16x22 mm
Weight
340 g