Introduction to underwater photography

Learning goal

You will be able to explain that water carries light very differently from air, and why an underwater photograph often comes out blue, green and pale. You will know that water swallows colors not at the same rate but in an order, red disappearing first and blue last. You will see that color loss depends not only on depth but also on the total path light takes through water, that is, on the distance to the subject. You will understand how small particles in the water scatter light and lower contrast and sharpness, and therefore why you need to get close to the subject underwater. You will notice how water changes a person's skin, and note the true color of that skin before the water.

The question

The instructor of the diving school in the cove shows your friend a series of photos on a tablet at the pier. All of them have the same red marker buoy. In the frame shot just below the surface, the buoy is bright red. A few meters down the red has darkened, turned brown. Deeper still, it is an almost black gray. The skin of the instructor swimming beside it has also shifted further toward gray and green in the frames. The buoy is the same, the instructor is the same, only the water changes. How does water swallow light?

Context

At the very start of this journey you saw that a photograph is a record not of an object but of the light falling on that object and returning from it (Lesson 1.1). In the golden hour and blue hour lesson you learned that molecules in the air scatter the blue part of light more, and that the low sun looks warm because of this, scattering in the atmosphere (Lesson 5.4). In the color lesson you also set the white balance, which balances a light source's color against a neutral surface (Lesson 11.2).

Air carries light with almost no loss; we can see the color of a mountain from kilometers away. Water, though, is far denser, and both swallows and scatters light. An underwater photographer's first lesson is getting to know these two effects before the camera, because almost every technique underwater is an answer to one of them.

Simple explanation

Why do colors disappear in order?

Selective absorption is water swallowing light at different rates according to its colors, using up the long-wavelength red first and the short-wavelength blue last. When sunlight enters the water it carries all the colors; as it goes down, red weakens first, then orange, then yellow. What reaches deepest is blue and green. That is why in a frame shot at depth, a red coral, a red fish or a red swimsuit turns brown, gray, even black.

This loss can't be fully taken back with white balance. White balance shifts the colors that are there relative to each other; but if the red the water swallowed never reached the sensor, there is no information to bring it back. Pulling the camera toward warm helps up to a point, beyond that it adds noise and broken tones to the frame. The way to really bring the lost colors back is to give the subject light inside the water, from a very short distance; you will see this later in the track.

Is only depth important?

The water path is the total distance light travels through the water from the surface to the subject and from the subject to the lens. What decides color loss isn't depth but this total path. Light goes down from the surface, strikes the subject, then comes horizontally through the water to the camera. In the frame of a photographer at four meters deep looking at a fish two meters away, the light has passed through six meters of water; if they look at the same fish from five meters away, the light passes through nine meters of water and more red is missing from the frame.

This explains perhaps the most basic rule of underwater photography: get close, then get a little closer. Underwater, building the same framing not from afar with a narrow lens but from close with a wide lens shortens the water path. Working in shallow water also reduces the loss that comes from depth; that is why, for beginners, the most color is close to the surface, where light is plentiful.

Why does water make the image fade?

Turbidity is sand, plankton and other small particles suspended in the water scattering light in every direction and lowering the image's contrast, sharpness and visibility. Even in a clear cove, water carries far more particles than air; after a storm, or where a stream flows into the sea, these particles increase. Every meter of water between the camera and the subject adds a layer of haze to the image.

Turbidity also depends on the water path: getting closer to the subject reduces the number of particles in between and the image sharpens. An angle with the sun behind you reduces the particles reflecting light straight into the lens. Water's effect on people shows here too: a swimmer's skin, whether light or dark, loses its red under the water, shifts toward gray or green, and blends into turbidity's pale haze. The easiest way to find the skin's true color later is to shoot a frame of the same person in the sun before they get into the water.

Visual evidence

The instructor explains how the frames in the series were shot. The same red buoy, at the same sunny noon, shot first just below the surface, then a few meters down, last deeper still. In the shallow frame the red is bright; in the next frame an orangey brown; in the deep frame only a dark smudge. The water itself has turned a darker blue as it goes down.

Then they show two frames at the same depth. In one they had come within an arm's length of the buoy, in the other stayed a few meters back. In the close frame part of the red can still be picked out and the buoy's edges are sharp; in the distant frame the red is almost gone, and the buoy is lost inside a pale haze.

Finally they open their own frames. The instructor is dark-skinned; in the frame shot in the sun on the pier, their skin is a warm brown. A few meters deep their skin has shifted toward gray and a greenish tone; the face of their light-skinned student beside them has turned to a bluish pallor. The instructor says they kept the pier frame as the reference for judging both their skin tones in editing.

Common mistakes

Summary

Water swallows light in order according to its colors through selective absorption: red first, blue last. Color loss is decided by the total water path light takes from the surface to the subject and from there to the lens, and turbidity lowers contrast and sharpness along this path; that is why underwater you get close to the subject, and the true color of skin is noted before the water with a reference frame.

Mini assignment

In this assignment you will observe what water does to light, even without a waterproof camera; a pool, a cove or an aquarium is enough.

1. Shoot, or carefully watch, three objects, red, yellow and blue, in the same light, out of the water and in the water, if possible from different distances; note in which order the colors fade.
2. Shoot an object inside an aquarium or a glass container twice, putting it right behind the glass and at the far end of the container; compare the contrast and sharpness.
3. With their agreement, shoot a frame of someone first in the sun, then in the water or from behind the water; put the two side by side and write down how the skin changed.

Check yourself

• Does the order in which the colors disappeared match selective absorption?
• How much did contrast and sharpness drop in the distant object, and can you explain it with the water path?
• Does the reference frame show the true color of the skin in the water?

Glossary

Mini quiz

1. Which color does water swallow first?

• A) Blue
• B) Red
• C) Green
• D) All at the same rate

2. In the frame of a photographer at four meters deep looking at a fish two meters away, how many meters of water has the light passed through?

• A) Two
• B) Four
• C) Eight
• D) Six

3. Why doesn't the red lost at depth fully come back with white balance?

• A) Because white balance doesn't work underwater
• B) Because the camera refuses to record red
• C) Because there is no information to bring back a color that didn't reach the sensor
• D) Because red turns into blue in water

4. How is the true color of a swimmer's skin in the water most easily found?

• A) With a reference frame shot in the sun before getting into the water
• B) By raising the saturation
• C) By pulling the frame toward warm
• D) By painting it by guesswork

Answers

1. B — Long-wavelength red is the color absorbed fastest in water.
2. D — The light goes four meters down, then comes two meters horizontally: six meters in total.
3. C — White balance can only shift the colors that are there; it can't produce the missing one.
4. A — A frame of the same person out of the water gives a comparison that shows the skin's true tone.

Summary card

• Water both swallows and scatters light.
• Selective absorption: red first, then orange and yellow, blue last.
• Water path: the total distance from the surface to the subject and from the subject to the lens; not depth alone.
• Turbidity: every meter a layer of haze; get close, then a little closer.
• For the skin's true color, shoot a reference frame before the water.

Bridge to the next lesson

The instructor's frames give your friend the wish to go underwater with their own camera. But not a single drop of water must touch their camera; the instructor carries their own camera inside a thick, transparent box, with a glass shaped like a half sphere at its front. How does a camera go into the water? The next lesson takes up waterproof housings, seals, and the care done before and after every dive.