Teleconvertors are supposedly optimized to work with telephoto optical design (where FL longer is than the distance from rear node to focal plane). There happened to be a thread about using 11-16mm lens with a teleconvertor, and physical compatibility between the two. I got to thinking about degradation of optical quality, using a supplemental optic in combination with a retrofocus optical design (Wide Angle), and decided to do a test.
First shot, Tokina 11-16mm lens with Kenko Pro 300 DG 1.4x (not the absolute latest design DGX), with lens FL set to 11mm, resulting in 15.4mm effective FL. Shot at indicated f/5.6
The Tokina set to about 15mm, shot at f/5.6
The center of the frame was positioned at about the E18 line of the right column, so the right column depicts Center performance, while the left column depicts Edge performace. I was quite pleasantly surprised at the result with the teleconvertor!
