Ok long title but im hoping this can be an ongoing discussion as technology improves.

I am a photographer and I love taking pictures of landscapes and animals and nature stuff. Ive done some pet photoshoots and cosplay photoshoots and I would absolutely LOVE to be able to offer my services to the mer community as more then just another tailswimmer. So for those of you who do take photos and video underwater, what do you use? What camera bodies and lenses do you find work best? Obviously underwater you cant swap equipment so what methods have you found for testing and then checking and making adjustments? What type of settings work best underwater? Do you use the same camera you use above ground but with a case or cover?

I currently have Canon Rebel t6i and a few lenses. Ive looked at some bags and cases for waterproofing your camera but that scares the he'll out of me. Im nervous to try because there's no coming back from a cheap product. Any advice or wisdom or links or thoughts to impart?