Hello -

I'm interested in purchasing the new Sony a7S III camera that should be out in a couple of days (September 23rd, 2020). It would be my first full-framed camera. It would also be the first time that I would spent a good chunk of $$$ on buying any kind of camera. Of course, I'd need to purchase appropriate lenses for this camera. Although the Sony brand lenses would work best for this camera, they're also expensive.

I see that Sigma makes comparable lenses for the E-Mount Sony cameras. For example, Sigma has the 24-70 DG DN Art lens that is nearly $900 cheaper than the Sony lens. I own a couple of Sigma lenses that I use for my Panasonic GH5 camera. Although I'm happy with the quality image of those lenses, they work best in manual mode rather than auto-focus mode. (Although, to be honest, the GH5 camera is known for its less than dependable auto-focusing.)

So. . . my questions. . .

How well would the Sigma E-Mount lenses work with the new Sony a7S III camera? Would the auto-focusing be dependable? How is the quality of images provided by these lenses for the Sony E-mount cameras?

Thank you for your thoughtful comments and opinions.

I've got the Sigma 24-70mm and 100-400mm on the Sony A7III and I'm very happy with them. The image quality is exceptional. I can't compare the autofocus performance to the G-Master lenses, but the reviews I've seen suggest that there's very little difference between them. I fact, their latest prime is apparently faster at finding focus than the equivalent Sony native lens.

A follow up to this. . .

I ended up purchasing one of the Sony a7sIII cameras, and a few of the Sigma lenses. Wow! It's an expensive investment, but I'm in love with this camera!! Those Sigma Lenses work great with fast and accurate auto-focus if/when needed. Wow!