one camera’s wide angle …

Berthiot Angulor 28mm for Leica. Made in Paris FR

Toronto. … is another camera’s telephoto. Did you ever wonder why the tiny smart phone camera has an equivalent 35mm camera size? For example my iPod Touch camera has a 3.3mm, f/2.8 lens but images it takes are considered to be equivalent to those taken with a 35mm lens on a 35mm camera – same angle of view.

As a general rule, a lens focal length about equal to the sensitive media diagonal is called a normal lens. A focal length of less than the diagonal constitutes a wide-angle lens for that camera/media while a focal length greater than the media’s diagonal size is said to be a telephoto or long focus lens. For example, most of us consider a 50mm lens as a normal lens for a 35mm camera. The film frame diagonal is about 43mm so the traditional normal lens is slightly ‘telephoto’. The smaller the sensitive media, the shorter the focal length of a normal lens and by extension both wide angle and telephoto lenses.

If you crop a wide-angle shot, the result can be the same angle of view as a normal lens or a telephoto – only the grainier look and lower resolution might give it away.  Because the majority of film photographs were taken with a 35mm camera, it became popular to show the tinier sensored digital camera as if it had a 35mm camera lens. Of course the un-cropped image from a shorter focal length lens gained a greater depth of field (think of the Minox subminiature). This made computerized images popular since the camera image could be changed to look as if a lower (wider) f/stop had been used with its narrower depth of field.

Attempting to use a lens designed for one size of media with another larger media may result in vignetting as the image’s illumination falls off before the edges of the media are reached. This was an issue in the days when camera bodies, plate holders, and lenses were all purchased separately; not specifically designed as a unit.

This entry was posted in history and tagged , , , , , , , , . Bookmark the permalink.