I'm a little over a year or so into owning an a9, the first one, not the a9ii (I thought I was slick saving $1500, and now I'm feeling kind of stupid). Tonight I shot some indoor basketball and was having some pretty significant banding issues, first time it had happened, and I was definitely not happy to say the least.
I've scoured the internet, and there doesn't seem like there is any fix if you're shooting with the electronic shutter (which is, of course, why I bought the a9 in the first place).
Anyone have any advice, or better yet, a solution?