Getting Good Blues Underwater
It is important to understand how the color blue looks in your photo, and what affects it. The best way to explain this is by example.
Shifting color temperature, blue color and strobes
You can tell your camera what color temperature you want your photo to be. If you tell in a lower color temperature than it really is, software will try to add blues back into the photo. If you tell it a higher color temperature that it actually was, reds and yellows will be added back in.
In the following example the light is coming from two sources, the sun, and my strobes. The light from the sun is lighting up the water, causing it to appear blue. My strobes are lighting up the foreground, coloring the lionfish and the barrel sponge red and reddish-purple. The color temperature of the light coming out of my strobes was around 4800K.
I changed the color temperature of the photo in my RAW editor to demonstrate what happens.
3500K - blues have been increased dramatically, causing the barrel sponge to look purple.
4000K - some blues have been added in.
4500K - the foreground subjects look close to their natural colors, and the blue water looks pleasant.
5000K - this is also close to the natural colors of the lionfish. The subjects may have been warmed up slightly. The blue water still looks good, although not as deep a blue as 4000K.
5500K - this photo is warmed up slightly, yellows are starting to be added.
6000K- now you can clearly notice the blue is not so blue and deep colored, and the sponge and lionfish look too warm.
6500K - the water is starting to look blueish-green, and you can see the yellow in the lionfish.
It's nice to have the foreground and background colors look nice. Use strong strobes, wide angle lenses, and get your strobes very close to your subject to avoid color loss. This will allow you to set the color temp close to your strobe's actual color temperature.
If your strobes are a couple feet away from the subject, reds and oranges will be lost. You'll have to increase the color temp slightly in the RAW editor to get the best foreground subject color, which we don't want to do.
We want the color temp to be as low, close to 4500K. This means using the warmest strobes possible for wide-angle, when shooting in blue water, like Ikelite or Subtronics. The warmest strobes means the lowest color temp.
Some strobes are cooler because cooler strobes can get more power from the same amount of wattage. S&S YS-01's, YS-110a's, and Inon Z240's and other strobes for compact cameras are all cooler strobes.
Cooler strobes can be gelled to warm them up. The cost is losing a little bit of output. The more you warm them up, the more light it costs you. Read more about gelling strobes to make them warmer.
Other factors affecting blue color
Proper exposure is important for good blues. If they are overexposed (too slow a shutter speed), they will look bright and "Washed out". Too underexposed (too fast a shutter speed), and the blues will look too dark. Try to get it just right, take a couple practice shots underwater.
Obviously, shooting in "blue" water that is clear, on a sunny day helps a lot.
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