Tonight I got my Explore Scientific ED80 in. I also ordered the field flattener, but I didn't know it wasn't for DSLR's. I tried it out anyway tonight since I couldn't wait to modify my t ring for the right backfocus tomorrow.
It was very windy, and I am just using a lightweight tripod, so I was only able to take 11 photos and had to limit my exposures to 20 seconds each. I am using my Pentax K-1 with Astrotracer so I am not using a tracking mount.
Anyway, for the short amount of total exposure, and the incorrect backfocus on the field flattener, I can already see that the ED80 is going to be a huge improvement to my new hobby of astrophotography. So long old soviet lens
Here's a quick edit from the session tonight,