Revolving fastener

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Revolving fastener from a Revere camera for 16 mm film

The rotary closure is an important component in film cameras and copying machines . The corresponding component in film projectors is called a rotating screen . In general, the rotary shutter consists of a circular sheet metal that rotates around its center and from which a sector is cut. The rotary shutter is mechanically rigidly connected to the film drive and closes the image window until the free sector releases the light (or the copier light) coming through the imaging lens at the right moment.

Depending on the construction of the camera film drive, the opening angle of the shutter is between 135 degrees (Bolex-Paillard H Reflex VS) and 235 degrees (Mitchell 16).

Revolving locks are permanently installed in the forms ; permanently installed, connectable ; adjustable and exchangeable . Adjustable wrap-around locks consist of two sheets of metal lying on top of one another, which can be turned against each other via a gear or lever. With them it is possible to change the exposure time, even during the exposure. Fade-in, fade-out and fade-out occur when the piece of film with a fade-out is rolled back in the closed camera before the fade-in.

Interaction between transport gripper and rotary lock

One embodiment of the rotary closure is at an angle of 45 degrees to the optical axis and has a reflective surface. The shutter deflects the light from the lens onto a focusing screen, so that the camera person observes the same section with the same depth of field as it falls on the film. This function was first implemented in the Arriflex camera from Arnold & Richter. The Arriflex shutter has a symmetrical shape with two wings and rotates at half the frame rate. There are also rotary closures that rotate around an axis perpendicular to the optical. Such a shutter runs around the entire mechanism and cuts the light bundle from the lens parallel to the bottom and top of the image. Camera designs of this type are those of Dr. John L. Henry Smith (1897), the Akeley "Pancake" (1911) and the Kinarri (1924).

The revolving fastener rarely has a conical shape, e.g. B. at the Ciné-Sept of Debrie (1921). Drum shape can be found in the Cinégraph Bol (1923), the Bolex Auto and other inexpensive cine-film cameras. The Aaton-Minima has a patented cone lock as an add-on that prevents stray light from the viewfinder from reaching the film.

In the case of step copying machines, there is also a rotary lock. The opening angle is generally smaller, between 170 and 90 degrees. Typical such devices are the Matipo Debrie , the Lawley Step Printer or the Uhler.

Exposure time depending on the aperture angle and frame rate

The formula applies

Cycle angle ÷ opening angle × frame rate = reciprocal value of the exposure time .

Example: 360 ÷ 170 × 24 → 1 / 50.8 second.

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