Star photography with an old Russian lens

Just for fun, I tried some astrophotography with an old (1976) Soviet-era Russian lens.  The lens is the Industar-50-2, (ИНДУСТАР-50-2) an M42 screw-mount 50mm f/3.5 lens.  This lens is remarkably tiny, only 68 g (2.4 oz).  It is a 4-element 3-group Tessar design.

This lens was designed to cover the standard 35-mm film format (what is now called "full frame" with respect to digital cameras).  Some initial test shots with a Sony A7iii camera showed very strong corner distortions at f/3.5, so I instead switched to a smaller-sensor E-M5iii camera and shot at f/4.  Even so, star smearing is still evident in the corners of the frame. 

Here is an image of the lens mounted on the E-M5iii with an M42 adapter:

 The following images were obtained on Tuesday night under a bright waxing gibbous moon, so exposures were limited to 30 sec.  Measurements of star separations show that the lens has an actual focal length of 52.7 mm.  This is consistent with many so-called "50mm" lenses from the film era, which were often closer to 52mm as revealed in lab tests publshed by Modern Photography and Popular Photography magazines.

I used a Kase AstroBlast diffusion filter held in front of the lens.  The lens has a non-standard 35.5-mm filter thread, which is incompatible with my screw-in filters. 

 

Saturn rising over Snowshoe Mountain

Constellation Lyra.  Vega is the bright star.

part of Cassiopeia

The Little Dipper barely fits in the frame.  Polaris is near the right edge.

The Andromeda Galaxy (M31) near center.