I am sorry to say... I found nothing remarkable about this lens, other than size.
The f4 is good enough because everything in focus anyway.
But no lens draw, per say.
Plus, on my Sony a7 it darkens the corners significantly.
This lens is a film era optical design not optimized for digital sensors. The rear element sits very close to the sensor, so toward the corners the incoming light hits the sensor at too steep an angle to properly enter the pixel "buckets". So you need to use Cornerfix or similar software to fix the corners.
Several from my Hill of Crosses gallery were taken with the 21 skopar!
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http://www.rangefinderforum.com/rffgallery/showcollection.php?cid=10436