LIGHT. The human eye can detect only a small portion of the light around us. Within the spectrum we can detect (the visible spectrum), our brain interprets different wavelengths of light as different colors, so shorter wavelengths (~400 nm) look violet and and longer wavelengths (~700 nm) look red. Wavelengths below about 380 nm (ultraviolet, UV) or above 750 nm (Infrared, IR) are invisible to humans. However, many other animals, including insects, do see in UV and/or IR light.

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 determine the colors in an image using three types of photoreceptors (cones), each sensitive to different wavelengths of light - red, green, and blue. Another type of photoreceptor (rods) only responds to light intensity. Depending upon the degree by which different cones are stimulated, the brain is able to distinguish at least a million different colors. But there is nothing intrinsically “red” about 700 nm light, nor “blue” about 400 nm light. When there is not enough light to stimulate the cones, 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 relative to the rest of the scene, could represent a threat so gets a high priority. However, detecting, processing and interpreting requires a finite amount of time, so some motion happens faster that we can perceive it. That is why movies, which are a series of static images presented at a rate of about 24 images per second, appear to us as continuous motion. Other motion, such as the beating of a humminbird’s wings, are even faster and appear to us as a blur.

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 that filter the information reaching 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. Not surprisingly, there are many similarities between human vision and how a modern digital camera works. 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 an electrical signal 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, a filter is placed over the camera sensor to block the UV and IR wavelengths (which our eyes cannot detect) 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. For example, a lens filter that blocks both UV and visible light will produce 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. For example, green plants appear as white when photographed in the infrared. 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.

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.