LIGHT. The human eye can detect only a small portion of the light it encounters. Within the electromagnetic spectrum (above) our eyes can only detect light with wavelengths between about 380 nm and 750 nm. Within this visible spectrum, our brain interprets different wavelengths of light as different colors. Shorter wavelengths look blue and and longer wavelengths look red. Wavelengths below about 380 nm (ultraviolet, UV) or above 750 nm (infrared, IR) enter our eyes but we have no way to detect them. However, many other animals, including insects, do see in UV and/or IR light. Bees, for example, rely on their ability to see in the ultraviolet to more efficiently locate pollen in flowers, while many female birds use their UV vision to scrutinize male plumage when selecting a mate. Reindeer and white-tailed deer use their UV vision to detect predators, spot urine trails and locate food. Butterflies have more than a half-dozen different types of photoreceptors while some shrimp have as many as 16 separate photoreceptors. Salmon, bullfrogs, bats, mosquitoes and snakes are among the many animals that can detect infrared light. Conversely, many marine, nocturnal or borrowing animals, such as seals, sea lions, walruses, dolphins, whales, owl monkeys, raccoons, and some rodents, lack color receptors altogether, and see the world entirely in black and white.

COLOR. Colors are all in our head. Our brain creates what we see as color as a way to better distinguish details in the world around us. In fact, there is no way to determine if the color one person sees as red, for example, is the same as what another person sees as red. Our retinas respond to the light striking its surface using three types of photoreceptors (cones), each sensitive to different wavelengths of light - red, green, and blue. Another type of retina photoreceptor (rods) only responds to light intensity. Depending upon the degree by which different rods and cones are stimulated, the brain is able to distinguish at least a million different combinations of wavelengths, which our brain interprets as different colors. But there is nothing intrinsically “red” about 700 nm light, nor “blue” about 400 nm light. Cone receptors are much less sensitive to light than the rods, so when light intensity is low the rods take over, and our colorful world fades into black and white.

MOTION. Unlike a camera, which captures static images, vision is a continuous process. Our brains are continuously monitoring the input from our eyes, looking for information that needs to come to our consciousness. Motion, where an objects position changes relative to the rest of the scene, could represent a threat so gets a high priority. However, detecting, processing and interpreting motion requires a finite amount of time. Motion that happens significantly faster than the time it takes to process a visual image becomes a blur or invisible to us, which is why we cannot resolve the beating of a hummingbird’s wings or see a bullet traveling from the barrel of a gun. Conversely, our brains perceive continuous motion from from a sequence of static images, such as in movies, which are actually a series of static images presented sequentially at a rate of about 24 images per sec.

SUMMARY. What we “see” is not a completely faithful representation of reality. Our vision is constrained by the limits of the photoreceptors in our retinas, the speed of our image processors (brains), and the brain’s evolutionary biases and evaluation systems that filter what information reaches our conscious level.

REVEALING MORE REALITY THROUGH PHOTOGRAPHY

A camera offers the ability to control and vary the parameters that affect an image in ways that are not possible with human vision.

HOW A CAMERA WORKS. A camera offers the ability to control and vary the parameters that affect an image in ways that are not possible with human vision. In a modern digital camera light is focused through a lens to project an image onto a light-sensitive sensor. A special filter on the sensor surface divides the light into red, green and blue streams. The sensor generates electrical signals based upon the intensity and location of the light striking the sensor surface. A smalll computer calculates the color for each location on the sensor based on the relative amounts of red, green and blue light at that point and the immediately adjacent points. The resulting two-dimensional array of color and intensity information is then saved as a data file that can be viewed on the camera’s screen, a phone, a computer, or printed. Film cameras work in a similar fashion except that the film contains chemicals that react with light of different wavelengths to record both color and intensity information on the film itself.

PLAYING WITH WAVELENGTHS. The sensor in a modern digital camera can detect ultraviolet, visible and infrared wavelengths (approx 250 nm to 1200 nm). In order to make images appear natural, there is a filter over the camera sensor to block the UV and IR wavelengths (which our eyes cannot detect) in order to produce an image that better matches what we see with our eyes . Removing this filter creates a “full spectrum” camera. Photos taken with a full spectrum camera look strange because we are not used to seeing images that include UV, visible and IR light. By placing appropriate filters over the lens of a full spectrum camera, a photographer can select which wavelengths he wants to use for his images (see below). For example, a lens filter that blocks both UV and visible light produces a photo that shows what the world would look like with only infrared light. Because our brains do not understand the concept of color outside the visible spectrum, these images appear to us as black and white. Similarly, a lens filter that blocks visible and IR wavelengths will produce images showing the world as it appears in the ultraviolet, as some insects see it.

Example. The first image (visible spectrum) is how our eyes see the world. The center image (full spectrum) includes UV + visible + IR light. The higher intensity of IR light combined with its strong reflectance from vegetation overwhelms the visible light in this image. The pink color is due to the strong reflectance of IR light around 750 nm which is at the interface of the visible and IR spectrum. In the last image (IR spectrum) both UV and IR light are blocked from the sensor, showing the scene in IR light only.

ALTERING TIME. The Japanese photographer Daidō Moriyama once described photographs as “fossils of light and time”. Unlike our vision, which is continuous, photographs are static images captured during a specific slice of time. By controlling how long, or short, that slice of time is, the photographer can create images that are otherwise beyond the reach of human vision. For example, the beating of a hummingbird’s wings are so fast (about 50 beats per second) that they appear blurry to our eyes, But by creating an image in a very shot slice of time (eg. 1/1000th sec) we can freeze the hummingbird’s wings in mid-beat. Conversely, we can create images using much longer slices of time (eg. seconds or minutes) to reveal slower motions like the movement of stars or complex motions like the flow of water in a stream. Finally, moving the camera while it is recording an image (intentional camera movement) can produce interesting abstract images.

SEEING IN THE DARK. Because our vision is a continuous process, what we see is dependent on the light available and the sensitivity of the photoreceptors in our eyes. As mentioned above. with a camera it is possible to image a much longer slice of time. By allowing the camera’s sensor to collect light over longer time periods, the camera essentially accumulates light information, capturing images that are otherwise to faint for our eyes. Furthermore, unlike the cone photoreceptors in our eyes, the sensitivity of the camera’s digital sensor to color is not affected by light intensity. With sufficiently long exposures, for example, it is possible to produce a color image on a dark night that appears to have been taken in daytime - except for the stars in the sky.

SUMMARY. The camera is a fantastic tool that can capture beautiful images of what’s happening around us. Through its ability to manipulate light and time, the camera also opens up creative possibilities for visualizing the world in ways that our senses cannot reveal to us directly.