Today we’re going to explore colors, and how depth and water conditions affect light and photography. We learned about this in our open water dive class, but let’s review since some of us took that class a long time ago!
Even on the sunniest, clearest day, 50% of the brightness is lost in the top three feet of water. The first reason is reflection; a portion of the sun’s rays strike the surface and bounce away. Refraction accounts for another portion; light is bent as it passes through water and does not continue in a straight line. The third reason is diffusion; when light passes through water the beam becomes scattered. These three characteristics of light occur on the calmest days – add in some choppy waves and you will have even less available light. Waves also stir up sand and other foreign particles, further blocking or diverting light. It’s a wonder we can see anything at 60 feet!
The different wavelengths of light penetrate to different depths when they pass through water due to the process of absorption. Absorption occurs when light is converted to heat, and the longest wavelengths with the lowest energy are absorbed first. You’ve noticed how colors change when diving to different depths, but did you know that red disappears at less than 15 feet? Following our colors of the rainbow, orange is next at around 25 feet, yellow at 35, green at 65, and finally blue is absorbed at around 200 feet.
(In the photo above, the woman is floating just a few feet under the ocean's surface. As a color contrast, the reef is approximately 15 feet below her in clear, calm water.)
Between reflection, refraction, diffusion and absorption, we don’t have a lot of light to work with when we are scuba diving. This is why using a video light or strobes is important for photography – using a light source adds the missing colors back into the visible spectrum and allows us to see the underwater world as it truly is.
Using a light source is not the complete solution to perfect pictures, though; light needs to be used in a purposeful way to get the best possible outcome. Things to consider are type of light source, number of lights, positioning, and proximity to subject. We will touch on these briefly and get more in-depth in future blog posts.
Let’s start with proximity to subject. The light source for your photos is bound by the same laws of physics as rays of sunshine so you want to position yourself as close to your subject as possible without disturbing whatever animal you are photographing. You want the light to travel through as little water as possible (because it also has to bounce off your subject and come back to the camera). If you are too far away the light will be refracted and diffused and the colors will be weak as the light dissipates. Objects underwater will appear further away and larger due to the way light bends in the water (refraction again), so keep that in mind as you slowly approach thatfrogfish.
Another reason to get close is to eliminate as much floating debris in the water as possible between the camera and the frogfish; the bits of sand and other particles will catch the light and show up as “backscatter.” Even if you didn’t know this term, you’ve seen it in photos – tiny dots everywhere, sometimes big enough or numerous enough to ruin an otherwise great photo. Backscatter can be exponentially increased if someone is kicking up sand on the bottom; great buoyancy will help prevent us all from adding more unnecessary floaties into our shots.
Backscatter can also be partially eliminated by strobe positioning. With the light sources positioned to the sides and ahead of the camera, pointed forward, the light will strike the subject but leave the column of water directly in front of the lens unlit. Those particles in front of the camera, but in the unlit area, will not pick up the flash and cause you to spend hours on your computer using the spot removal tool.
What type of light should you use - a strobe or a video light? Or one of each? Or two strobes? The main difference is the output – a strobe can be as much as five times brighter than a video light, and better to freeze fast motion; and using short bursts of power, the battery time will be much greater. On the positive video light side, you can light up your subject and shoot in burst mode while your friend with the strobes took one photo is waiting for them to recycle. Video lights also have the ability to show you exactly what your picture will look like through your viewfinder. There are pluses and minuses to both types of lights, and we will dedicate more time to just this subject later.
If you are a macro enthusiast, one strobe might be all you want or need to brighten up a small critter. If you are more captivated by wide-angle landscape shots, go with two strobes. Most strobes can be used as video lights when you notice the turtle lazily swimming by, but if you prefer video over still shots, get a dedicated video light. The best part of underwater photography is experimenting with gear and figuring out what works best for the types of photos you want to take.
With either setup of lights, check your exposure at different depths and adjust as needed. What might be enough light at the deepest part of your dive will most likely be too much as you approach your surface stop and take photos of the fish lurking under the boat. Dial back your strobe power and take advantage of what natural light is penetrating to 15 feet.
We’ve only briefly discussed underwater lighting, so be sure to check back for more in-depth information on the types of lights that are available. Follow us on Facebook to see all the blog posts, as well as store specials and upcoming classes.