I am now seriously considering buying the Sigma FP, which looks amazing, to complement my Sony a7iii. On specs, the Sigma FP looks amazing, but I have the following concerns:
1. Battery life - how long can you use it? Obviously I could stick a USB power bank on it, but that kind of defeats the purpose of a small camera right?
2. Will anyone make an affordable variable-ND mount adapter for it? On my Sony a7iii I mostly use Nikon primes, and have an amazing (and cheap) mount adapter where I just turn the ring to seamlessly control the exposure. It's beautiful and there's definitely space for it with the L-Mount's short flange distance, but as far as I can tell this product doesn't exist yet. I could use my Matte-Box which has been gathering dust for years now, but really I cannot stress just how incredible having a variable ND filter in the lens mount is.
3. Will cropping/lossless digital zoom be useful and easy? The Sony a7iii excels in this, and makes it easy to use one prime lens at multiple focal lengths with no loss of quality. The Sigma's sensor is big enough, just need to know if it has that functionality.
4. Can you see the screen in bright sunlight? I like to shoot outdoors. I could buy a separate EVF, but that's pushing the price up more, as well as probably putting more stress on the battery.
So those are my concerns, does anyone have any experience to share with this very promising camera? With Canon and Sony both coming out with new cameras soon the field is very competitive, but the Sigma FP does look like a strong contender.