How a Camera works & Pinhole Photography… Yippeee!!!
Aperture Focal Point / Plane Lens Circles of Confusion An optical image entering the lens is made up of very “tiny circles of confusion.” When the circles of confusion are small enough they are called “points” and the optical image is considered to be in focus. Thus… points of focus or “Focal Point (Plane)”
Rays of Light Lens Focal Plane or Focal Point where the image is in focus. • The lens focuses the image on the focal plane. • Any movement of the lens or the film forward or backward increases the size of the circles of confusion and takes the image out of focus. • When the aperture is stopped down, the resulting circles of confusion that are in the front and the back of the focal plane become smaller and smaller and are regarded by the human eye as being more like points of focus. • This is depth of field.
A pinhole camera has infinite depth of field because the pinhole creates circles of confusion more or less the same as the pinhole all over the inside of the camera, and the circles of confusion are small enough to be regarded as point of focus. That means the photograph has a high enough resolution (resolving the points of focus) to be acceptable as a coherent image.
Rays of Light Pinhole Camera Hole Film (Focal Plane where the image is in focus.)
Exposure Exposure is how much light hits your film. Exposure is controlled by FOUR factors. Emulsion Sensitivity ASA/ISO Light Interval of Light / Shutter Speed Aperture
Light • How much and what kind of light you use • helps determine exposure. • Because…. • If something has a light sensitive emulsion then the more light you expose it to, the more it will be affected.
Emulsion Sensitivity • Film speed is measured in ISO or ASA The ISO is the International Standards Organization Not to be outdone, we have the ASA or the American Standards Organization (which has now been renamed the American National Standards Institute or ANSI) Some examples are… 50, 100, 125, 200, 400, 800, 1600, 3200, 6400 The formula for determining film speed is long, involved and highly mathematical. Therefore, we won’t go in to it except to say... Conveniently, ISO numbers and ASA numbers are, for the most part, the same. A high number is faster than a slow number and therefore reacts more quickly to the light.
Aperture 3.5 4 5.6 8 11 16 • Aperture is how big lens opening is. • The measurement is determined by the angle of the shutters covering the rest of the whole. • Each stop cuts the amount of light in half.
Shutter Speed How long the hole (shutter) is open. Some Sample Shutter Speeds: 1, 2, 4, 8, 16, 32, 125, 250, 500, 1000, 2000 This and all the other concepts that we have discussed today will be explored further. But for now, let’s talk a little about the history of photography…
Camera Obscura (Dark Room) Principles of photography first discussed by a Chinese philosopher, Mo Ti or Mo Tzu who lived in the 5th century BC. And further discussed by Aristotle in the century following. The first discussion of something resembling a camera obscura was by a Persian (Iraqi) Abu Ali Al-Hasan who lived in the 10th Century.
Used initially only by scientists, the camera obscura was used by artists such as Leonardo da Vinci as early as the 15th Century.
A precursor to movies, camera obscuras were used as an early form of entertainment. It wasn’t until 200 years after the camera obscura was first developed that the chemical developments necessary for contemporary photography were discovered.
It was these same philosophers an scientists Mo Ti, Aristotle and Ali al-Hasan who first discussed the concept of the pinhole camera and it’s usefulness as an aide in viewing the sun and eclipses. By the 1800s, pinholes were being used in a variety of way to actually take photographic images. The ease of the pinhole camera is that it can be made from just about any light-safe box.
Some examples of pinhole photos...
Marianne Engberg, Greenland series 7” diameter pinhole 1980
Eva Westerland, Tightrope from Solitary Traveler series 81/2 x61/4 1999
Jochen Dietrich, Self Portrait 3.5x3.5 from Clock Camera 1993
Jeff Fletcher, Bromide Eggs Eggshell coated with “liquid light”, then placed inside pepper shaker, each image is made with one pinhole lens, photograph of 18 pinhole images 1989
Willie Anne Wright, Sleeping Confederates from the reenactment of the battle of Chacelorsville 8.5x6.5 1988
Walter Crump, Scribe (Islamabad Pakistan) 10x10 Bleached & Toned 1992