Can you explain this further? If it is true, how are all those wonderful pictures taken by cave divers in places like the Bahamas, with formations much more than 3-6 feet away?
Many times they are using optically triggered strobes positioned off camera to illuminate the formations or whatever. Sure, you can bump the ISO up, slow the shutter, open the aperture and pump the strobe up to full blast and with two strobes you can maybe get a shot out to 6 to 8 feet, maybe a little more but the results will not be the same as close up. You will get better color, less illuminated debris blossoms and a more clear shot if you are up close. Which is why people who are new to UW photography misunderstand the purpose and importance of WA lenses. They are used to get CLOSE and still get the subject in the view finder and stay within strobe range.
Doubling the distance quadruples the power needed. The light diverges, you do the math, the area of a circle is:
d^2 * 4/(d^2) = 4
So, good luck with lighting up a whale shark or shooting your nephew on the fooseball field from the middle stadium row with that little Instamatic (that would be an old 120 film camera with a flash cube, lol).
I bet looking at this photo, which I sort of like, you think the non-illuminated reef in the back ground is way back there and about 20 feet distant and the near whips about 10 feet. Nooooo, the whips are nearly touching my lens, about 6 inches, and the reef behind is at most five feet. I was shooting in Av, aperture to 5.6, twin Inon D2000 set at f.2.8 inn Auto with a 150 degree FIX fisheye lens.
The turtle is at about six inches to one foot, f5.6 on the lens, Av mode, Inon strobes in Auto at f.5.6:
How far you think this squirrel fish is from my lens, well, about one foot, camera in Program, strobes in sTTL:
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