No one knows exactly when or how it happened, but at some time in ancient history, someone noticed that when light came into a darkened room through a small hole, it created an upside-down (and laterally reversed) image of what was outside on the wall opposite the hole. Centuries later, this optical principle was given the name camera obscura, which is Latin for “dark room.”

The earliest mention of a camera obscura was by the Chinese philosopher Mo-Ti in the fifth century b.c.e., who called the darkened room a “collecting place” or “locked treasure room.” The Greek philosopher Aristotle also recorded the optical principle of the camera obscura after he viewed a solar eclipse through the holes of a sieve and through the tiny gaps between the leaves of a tree.

In the tenth century, Arabian scholar Ali Al-Hazen Ibn Al-Haitham, also known as Al-Hazen, used a portable camera obscura to observe solar eclipses. An expert in philosophy, physics, and mathematics, Al-Hazen was a serious researcher. He was the first to explain how the eye can see. Among his many other observations was the fact that the image projected by the camera's pinhole became sharper as the hole became smaller.

Bringing Things into Focus

The earliest camera obscuras were primarily used for observing solar eclipses and other scientific applications. The images they projected remained primitive, as only the size of the pinhole could refine them. In the sixteenth century, a focusing lens was added to the pinhole opening, which sharpened the images that appeared on the viewing wall. The lens also made possible a bigger pinhole that would let in more light and create larger and better images. Another important advancement was a mirror that turned images right-side up and reflected them onto a viewing surface.

Once the camera obscura had practical applications, artists and draftsmen used the table-top-sized devices to project images onto paper that they could then trace with pen, charcoal, or pencil. Over time, the camera obscura was refined and made even smaller so it could be used in the field. However, there was still no way to permanently capture the images themselves for later use.

Technological Advances

Hundreds of years before the photographic process was invented, people had already noticed that certain objects and elements changed color when left in the sun. What they didn't know was whether these changes were caused by light, heat, or air.

In 1727, German professor Johann Heinrich Schulze decided to perform experiments to determine whether heat would cause silver salts to darken when he baked some in an oven. It did not. He then decided to test light's effect on the chemical. He carved some letters out of a piece of paper, stuck the paper to a bottle filled with the salts, and placed it in the sun. The sun darkened only the exposed parts of the chemical. The parts underneath the paper remained lighter. He had the answer to his question.

In the early 1800s, Frenchman Joseph Nicéphore Niépce (pronounced “neep-ce”) captured the view outside his window by placing a sheet of paper coated with silver salts at the back of a camera obscura and exposing it through the lens. Since he didn't know how to protect the image from further exposure, however, it eventually vanished when the paper was exposed to full daylight. But Niépce was inspired to experiment further.

Several years later, he devised a way to make a permanent image on a metal plate coated with bitumen, another photoreactive substance. It took about eight hours for the image of the view from his window to form on the light-sensitive material. Niépce called his process heliography, meaning “sun writing.”

The Daguerreotype Develops

Louis Jacques Mandé Daguerre, another Frenchman, was experimenting with photoreactive chemicals at the same time as Niépce. A noted artist, Daguerre regularly used a camera obscura as a painting aid, and he wanted to find a way to make images last. He learned of Niépce's work in 1826 and formed a short partnership with him that ended when Niépce died in 1833.

After his partner's death, Daguerre continued his quest for a permanent image. Instead of heliography, however, Daguerre worked on developing a new process that would yield faster exposure times.

The daguerreotype, as Daguerre called his process, was a significant advancement in the quest for a permanent photographic image, but it still had many flaws. The image was transferred onto a polished, mirror-like surface of silver halide particles produced by iodine vapor. Since it was a positive process, it only yielded one-of-a-kind images, and the photographic plates were extremely delicate. Exposure times were still lengthy, about thirty minutes or so, which ruled out portraiture.