I Am (Was) A Camera

Here are some old analog photography notes from days gone by. Still relevant, but without the techno terminology and the acronyms associated with today’s modern digital cameras. In fact, you might be interested in the analog definition of photography. Then, following that are some more analog notes on photography. To digitize the text, just substitute the word sensor where appropriate.

The Analog Definition of Photography

The fundamental physical principle of photography is that light falling briefly on the grains of certain insoluble silver salts (silver chloride, bromide, or iodide) produces small, invisible changes in the grains.  When placed in certain chemical solutions known as developers, the affected grains are converted into a black form of silver.

When a photograph is taken with a camera, light reflected from the object passes through the shutter, diaphragm, and lens to form a real inverted image.  For the brief period during which the shutter is open, this image falls on the surface of a film or plate sensitized by silver salts and causes an invisible latent image to be recorded on it.

An Analog Explanation of the Camera

A camera consists essentially of a box carrying a lens, diaphragm, and shutter that are arranged to throw an image of the scene to be recorded onto a sensitive film or plate. The lens is usually made up of several components. It forms a real, inverted image of the object. In the popular 35-mm cameras the focal length is typically 50 mm (2 in), but it can be shorter or longer according to the size of the camera. In the focusing mechanism provision is made for moving the lens backward or forward to focus the image on the film. Three main methods are used to determine the position of the lens for correct focus: focusing scale, range finder, and reflex finder.


Two types of shutters are commonly used. The between-the-lens shutter is mounted between the components of the lens. The focal-plane shutter consists of a roller blind containing a slit that moves rapidly across the plane in front of the film. In popular cameras the shutter provides a range of exposures from about 1 second to 1/1,000 of a second. The diaphragm may also be placed between the components of the lens. It provides a circular hole of variable size that regulates the amount of light that reaches the film.

If the light is weak, or if a short exposure is required, the diaphragm is opened wide to admit sufficient light. Under good lighting conditions with moderate exposures the diaphragm is set to a smaller aperture, thus reducing the amount of light reaching the film. The smaller aperture can also reduce effects of aberrations and of any error in focusing, thus producing a sharper picture (i.e., depth-of-field).

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