Annabelle Weeks, age 12, of Houston, Texas, for her question:
How did photography~get started?
Many of us used the great grand daddy of the camera during the last solar eclipse. We set up a white screen facing the sun and pierced a pinprick in a sheet of paper. We held up the paper so that the sun shone directly through the tiny hole. When we focused it at the right distance a small, shadowy image fell onto the screen. We watched the dark disk of the moon creep across the face of the sun without risking our eyesight by looking directly at the dazzling event.
Most likely the story of photography started in some sunny climate where thoughtful people had time to observe the play of shadows and bright sunshine. Some 2_000 years ago, Aristotle described how he watched the image of a solar eclipse through the tiny 'poles of a sieve. In the Middle Ages, this principle was used to build a very special dark room called the camera obscura. The models were sturdy chambers often adorned with pillars and turrets.
The models changed, but the basic principle of the camera obscura remained the same. In the center of one of the solid walls there was a small hole or shutter. A beam of light came through and fell upon the opposite wall inside the room. The rays of light carried a photographic picture of the scenery outside and shed a shadowy, upside down image. When the light from outside was shut off, naturally the fascinating image disappeared.
In later centuries, lenses were added to sharpen the pictures and to turn the image right side up. Then in the 1550s, an Italian inventor added a stroke of genius to the camera obscura. He used a pencil to outline the shadowy image and later added colors to create a permanent painting of the scenery. This became a very stylish pastime and all sorts of new models were invented. One convenient camera obscura was a darkened sedan chair, with lenses on top and a mirror to reflect the image onto a drawing board held on the artist's lap. Another model used the same devices inside a black tent.
Through the 1600s, the camera obscura blossomed forth with a portable model and a desk model. By improving and adjusting lenses and shutters, artists created panoramas of outdoor scenery and even portraits. Then a Dutch professor stumbled upon a method to fix the shadowy images with chemicals. After many improvements, this idea finally led to our modern method of making permanent photographs on film.
In 1725, Professor Johann Heinrich Schulze was attempting to make phosphorous in his lab. Silver was present in his ingredients as an impurity and he noticed that his mixture turned purple when exposed to a lighted window. Schulze and later scientists traced this phenomenon step by patient step. Eventually it led to the use of silver salts to fix the camera image on film. The age of chemical photography began and the fascinating old camera obscura at last went out of style.