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I'd echo what others have said about the drawbacks of GoPro. That said, you can't argue with the form factor. It's small!
I just returned from a week photographing in the Cayman Is. I had my rig with arms and strobes. Yeah, nice pics.
But my buddies with GoPro came up with nice stuff, and to address the other half of the OP's initial question, their video light made a perfectly acceptable low cost dive light:
Suptig Diving Light High Power Dimmable Waterproof LED Video Light https://www.amazon.com/dp/B07315JD78/ref=cm_sw_r_cp_apa_NtsPBb4V42R13
So, yeah the Oly will be a reasonable choice. But to answer the OP's question, a GoPro and this light makes for a very cost effective way to get started (AND have a fair dive light).
I was surprised (and chagrined) at some of their pics, given what I've spent on gear.
I use a Sealife Micro with a tray and SeaDragon video light. The light is not a strobe, but still makes for very good photos. Plus, I use the light as my primary when night diving, which is HUGELY BRIGHT.
Note too that the Micro is a sealed camera, with no housing to leak or need maintenance.
View attachment 480917
That's amazing.... can't believe...Here's one of my buddy's GoPro pics with that cheap light from Cayman...
View attachment 480929
This upload is not at full resolution, but you get the idea. A Hero 4.
How long does light last say for continuous use in night dives?
How deep can sea life go without a housing for water proofing?
There's another option for video that's interesting too: Paralenz. It has a depth sensor and adjusts color correction realtime based on your depth (and also gives you a nice depth OSD if you want it in your videos). I don't own one but I've heard good things. Review: Paralenz Underwater Action Camera – DeeperBlue.com
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