Interesting text @evildeathcore, upvoted, but you have made one mistake:
Fisheye. There was also such a lens in my park. It was Peleng-8A, 3.5 / 8 mm circular Soviet fisheye. I shot it for 1.5 years and also sold it to a friend. Impressions are positive, but after buying a fullframe 5d, he began to give a round image.
Fisheye lenses do give round image. Peleng has not started to give round image, it was designed to give round image on full frame. You've made a mistake selling it, because I doubt you will find better fisheye in that price region. Maybe Samyang?
With the transition to a full frame, Peleng began to give a round image and thus became unnecessary to me. And I do not want to buy another diagonal fisheye for a full frame, since I played enough ... although I'm a little bored with such distortions.
I am more interested in a wide-angle lens with corrected distortion, such as 17-40 L