You asked
Is the sigma 85mm f 1 2 dg art worth it?
Worth it if you shoot people in dim light and want the softest backgrounds you can get. The Sigma 85mm f/1.2 DG Art is Sigma's flagship portrait prime. It has autofocus, no stabilisation, and it's made for full frame. It mounts on Sony E and L-Mount, so check the lens page to confirm your body is listed.
On full frame, 85mm is the classic portrait length. The portraits guide points to an 85mm f/1.8 as the workhorse for most people. The f/1.2 buys you more light and a creamier background, and that matters most when you're shooting wide open indoors or at dusk. If you mostly shoot in daylight or are on a budget, I'd start with the cheaper 85mm or the 50mm on the same page. The sensor sizes page covers when full frame is worth the extra cost.
Written by Claude from this site's pages.