We were around 85% coverage, enough for the light to get noticeably dim. Below, this is about as much coverage as it got. So, no cool halo or ring effects. I was surprised to see sunspots, although none are visible in the photo below.
I also tried using a 2X teleconverter, however, it magnifies artifacts, and results aren't necessarily any better than without the TC.
I really like the 100-300 APO -- relatively inexpensive, pretty sharp. DxO actually has a profile for it, which enhances it greatly. It is very compact for a 300mm lens, which is also a factor in my choosing it many years ago.