ggibson
Contributor
I have never tried taking photos while filming on my RX100 II, because it seems like a feature with a lot of compromises. You get a smaller file with JPG-only and no strobe. If you really want to try it, use a strong video light I guess. I have done dives where I mounted a Sony actioncam to the top of my camera housing when I wanted video and stills. But it's better to concentrate on one thing at a time--video or stills--to get the best results. There are a lot of things to think about when diving and shooting at the same time. I would rather get 1 stellar image than 100 mediocre shots. So now I just focus on shooting stills, and maybe take a video or two for fun.
On the topic of which RX100 model to get--the RX100 II is almost definitely worth the small price difference over the first model at this point. Much faster flash recycle time, better AF, better low-light performance.
The RX100 III and IV have some nice improvements over the II, but the lens change is debatable. The 24mm wide end makes it less compatible with wet wide lenses that are made for 28mm zooms. Also, the long end only being 70mm can be more limiting for macro situations, despite having a wider aperture. If you're using strobes, the wider aperture is less necessary.
On the topic of which RX100 model to get--the RX100 II is almost definitely worth the small price difference over the first model at this point. Much faster flash recycle time, better AF, better low-light performance.
The RX100 III and IV have some nice improvements over the II, but the lens change is debatable. The 24mm wide end makes it less compatible with wet wide lenses that are made for 28mm zooms. Also, the long end only being 70mm can be more limiting for macro situations, despite having a wider aperture. If you're using strobes, the wider aperture is less necessary.