Submitted by Al …
(Adapted from The Encyclopedia of Photography ©1963)
A between-the-lens shutter is a diaphragm shutter, such as the Compur, Prontor, or Supermatic, which is located between the front and the back elements of the lens. The shutter is composed of a body through whose center there is a circular opening equal in size to the diameter of the lens. When the two component parts of the lens are screwed in front and back of this shutter, the shutter body takes the place of the ordinary tubular lens mount. The space between the lens parts also contains the shutter blades, which are thin leaves of metal overlapping to close the central opening. They pivot back into the outer casing in such a way that when the shutter is operated it opens from and closes to the center of the lens.
The simplest type of between-the-lens shutter has only two blades and requires no cocking. A limited range of speeds is available on these shutters, depending usually on the variations in the tension of the driving spring. This spring, which drives the shutter, is compressed as the release lever is depressed. The shutter begins to close the instant the blades are fully open.
The more complex shutters have a double action, two distinct
movements for opening and closing. For low speeds, a clockwork brake is brought into action to delay the closing, but in high speeds there is no interval between the completion of the opening and the beginning of the closing. These shutters may be set from one second to 1/800 of a second. The efficiency with which they operate varies from 100% at the slowest speed to 50% at the fastest. A powerful spring, which must be tensioned before each exposure, provides the power for operating this mechanism.
The between-the-lens shutter is the most common type of front shutter, although the before-the-lens shutter is used sometimes on box cameras and the behind-the-lens shutter on portrait cameras.
As opposed to this between-the-lens or diaphragm shutter (so called because of its proximity to the diaphragm), there is the focal plane shutter. This shutter operates directly in front of the film itself and has a rolling curtain which admits light through a permanent or variable moving slit, or an arrangement of metal vanes that achieves a similar result. Some cameras, the Speed Graphic for example, are equipped with both between-the-lens and focal plane shutters.
Just in case you decide that your shutter is not working correctly and plan to take it apart, here are two samples of what you are facing!
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