For information on how I first constructed this lens, go to previous gallery, at
www.pbase.com/edkowalski/crazylens

Yesterday I went a step further and inserted a disk of black plastic with a 9mm hole in the middle (no, I did not shoot it with a hand gun) to stop the assembly down to about f/8.
As suggested, results were rather different than my first set of images, with lens wide open.
Images below, with "cropped" portions following, to isolate the middle portions, where focus is much sharper.
Lens delivers much sharper results in the center, softening and distorting out into the edges and corners. I would say this is the result of a single element lens, convex both sides, with no attempt at correcting astigmatism. Older camera lenses with a single element of glass were usually flat on the backside and curved on the front, this corrected some of the aberration. Eventually compound lenses were developed, with multiple pieces of glass that canceled out these distortions. Good example is the "Cooke Triplet" design, a relatively simple design with excellent correction.

Please click on thumbnails to see enlarged.
All images are (c) 2017 E.J.Kowalski.
Thanks! Ed