Underwater Photography Calculator

This calculator models how light behaves underwater and what that means for exposure and strobe placement. Ambient light loss combines two effects: a baseline of roughly one stop lost per 10 meters of depth (typical broadband attenuation in clear water) plus an additional term scaled by a water-clarity coefficient that you select — clear tropical water, temperate water, or murky water, each with a different attenuation rate. Color loss is modeled separately from brightness loss because water absorbs wavelengths unevenly: red disappears fastest, roughly one stop per 1.5 meters (essentially gone by 5m), orange fades at about one stop per 3 meters, and yellow survives longest at roughly one stop per 8 meters — which is why unfiltered underwater shots below a few meters trend blue-green even when perfectly exposed. Strobe range assumes a guide number underwater equal to only about one-third of its rated guide number in air, reflecting scatter and absorption losses in the water column; dividing that reduced guide number by your aperture gives maximum effective flash distance, and the calculator checks whether your specified subject distance falls within that range.

It also accounts for refraction making underwater subjects appear about 25% closer than they actually are — relevant for framing and for autofocus behavior, not for the physical light calculations above. Backscatter risk is a simple rule-of-thumb classification based on subject distance and visibility, not a precise model, since backscatter also depends heavily on strobe angle and particulate density that aren't captured here. Recommended maximum shooting distance uses another common rule of thumb: stay within about one-fifth of the reported visibility.