I had two CZJ 150mm lenses with me that day, and used the coated Tessar first - as I had done on all the other colour shots I took. Then the thought struck me that the uncoated Doppel-Amatar should be good in this situation, and did a second shot with that lens.
Exposure was by pure guesswork, since the only light meter I had was a Leningrad selenium meter. "Average" doesn't really help much in a situation like this, so in the end I went with f:16 at 1/10 second - it would have been 1/50 at f:16 outside in the open.