Yo, late to the party but I gotta chime in here cuz I have been through the ringer with this exact setup. Honestly, I spent years trying to avoid the "Sony Tax." I picked up a Sigma 35mm f/1.4 DG DN Art for Sony E thinking it would save me some cash for my music video work. Big mistake. I was filming this moody jazz set in a basement—literally NO light—and the AF kept pulsing and hunting. It was SO frustrating. I ended up with half my shots slightly out of focus and had to apologize to the client. Never again. Since then, I bit the bullet and got the Sony FE 35mm f/1.4 GM. Does it justify the price for low light? Unfortunately, it actually does. Here is the technical breakdown of why: 1. Linear Motors: The XD motors in the GM series are basically silent and don't hunt like the stepping motors in most third-party glass. In dark clubs where the contrast is low, that speed is EVERYTHING.
2. Light Intake: Moving from ur f/2.8 to f/1.4 lets in four times more light. ur gonna see a MASSIVE difference in ISO noise on ur a7S III. 3. Consistency: I have had issues with the Samyang AF 35mm f/1.4 FE II losing tracking when stage lights flare. The native Sony glass stays locked on the eyes. Lesson learned: for professional video, the frustration of missed focus costs way more than the lens. If the GM is too much, look at the Sony FE 35mm f/1.8—it's a total sleeper hit with great AF, even if it feels a bit "cheap" compared to the GM. gl! peace.

Respectfully, I'd consider another option. NGL, you dont need Sony glass for good AF anymore. The Samyang AF 35mm f/1.8 FE is half the price and works great in low light venues!

WATCH OUT for those cheaper third-party lenses because their autofocus often fails in low light... it’s honestly sooo frustrating when it hunts. Unfortunately, I’ve had issues with off-brand glass not being as good as expected for video. While the f/1.4 is great, the native f/1.8 primes are a solid alternative if the price is too high. Native is basically the best choice for reliable AF tho.

Like someone mentioned, native glass is basically non-negotiable if you want that sticky tracking. I freaking love the Sony FE 35mm f/1.8 as a budget alternative! It is a total beast for video. One technical detail that is huge is the focus breathing—this lens is super well-controlled compared to the Sigma 35mm f/1.4 DG DN Art. Also, the internal focus mechanism means the lens doesnt change length, which is fantastic for gimbal work. Honestly, dont get sucked into the f/1.4 hype for double the price... the a7S III sensor is so sensitive that f/1.8 is plenty. You get 90% of the GM performance for half the cost. Its a total steal for music venue work!

👆 this