I'm taking this GoPro HERO4 Black out to the Reef tomorrow.
It's attached to a floating handle (Fish Stick) with a tether.
It records 4k video with an incredible depth of field. It doesn't have a video back, though, so one hopes that something interesting is in the field of view. Or user skill is good.
Individual good frames can be extracted to .jpg. So some may be posted if I get lucky.
