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Film - Digital

Preset aperture - in lenses

With the first Single Lens Reflex (SLR) designed cameras the lenses were made with what is called a preset aperture. Because the light coming through the lens is redirected via a mirror to the view finder, when the aperture is set to the working aperture, (as in the picture f22) the amount of light coming through the lens is reduced to the point that it is difficult to see and focus on the subject. The view finder gets darker the more we stop the lens down.

Preset lenses were made with 2 rings one the photographer set to the working aperture say f22 and the other set to the maximum aperture of the lens in this case f8.

During focusing the lens was left open on f8 but just as the photographer was going to take the photograph they would turn the ring hard round until it stopped or locked at the preset working aperture and this would leave it set at the desired aperture for the exposure. They would then have to move the ring back to f8 to focus on the next subject.


As you can imagine they were not that easy to use.

A preset lens notice how there are two sets of aperture figures

How does aperture affect depth of field?
How are the f stop numbers worked out?
What is the difference between each f stop setting?


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