So I have a Sigma 10-20, used it a lot on my 7D. Good lens, loved the effects on the 10mm end. Bought a 6D last summer, wanting to get a ultra wide with it. I have my eye on the Canon 8-15 F4L. I looked as sample photos and saw the "circular" images, figured maybe they were created using a different style hood as opposed to a wide lens hood. While this effect would be interesting in some instances, I don't want that on most images. I understand that 10mm on a crop sensor is not as wide as 10mm on full frame. Just curious about where the extreme vignetting starts as far as focal range. I want something to give me the equivalent view of 10mm on a crop sensor. Wide, some distortion, but not the black circular "frame". Thanks in advance!