Rotary disc shutter
The circulation of closure is an integral element of film camera and copy machine, generally a circular plate which rotates around its center, and from which a sector is cut. The circulation shutter closes the Image Window and there are rigid mechanical connection with the film drive with its sector free for the light from the imaging lens.
Depending on the design of the camera film drive drops the normal opening angle of the shutter between 135 degrees ( Bolex Paillard H reflex VS) and 235 degrees out ( Mitchell 16).
Circulation closures, there are permanently installed in the forms; be fixed, detachable; adjustable and replaceable. Adjustable revolving shutters consist of two superposed sheets, which can be rotated through gears or levers against each other. With them it is possible to change the exposure time, even while recording. There arise Aufblendungen, fades and crossfades, if you roll back the piece of film with a dimming before fading up in the sealed camera.
An important embodiment of the current shutter is at an angle of 45 degrees to the optical axis, and has reflecting surface. The closure reflects the light from the lens into a so-called reflex viewfinder, so the camera person looks through the lens and the same section with the same depth of field watches as he falls to the film. This function was implemented for the first time in the Arriflex camera of Arnold & Richter. The Arriflex closure has symmetrical shape with two wings and runs at half the speed of the frame rate to. There are also current locks, which rotate about an axis transverse to the optical. The closure runs around the entire mechanism and cuts the light bundle from the lens parallel with image lower and upper edge. Constructions of this type camera are of Dr. John Henry L. Smith ( 1897), the Akeley, " pancake " (1911 ) and the Kinarri ( 1924).
Rarely has the revolving shutter keglige form, eg when Ciné -Sept of Debrie ( 1921). Drum form can be found at CineGraph Bol ( 1923) and at low-cost small film cameras. When Aaton Minima a patented cone closure is present as an additive, which prevents stray light enters the viewfinder to the film.
In step copying machines and a round closure is present. The opening angle is smaller because in general, 170-90 degrees. Typical of such devices are the Matipo Debrie, the Lawley Step Printer or the Uhler.
Exposure time as a function of opening angles and frame rate
The following formula
Cycle angle / angle × frequency = reciprocal of exposure time.
Example: 360 ° / 170 ° × 24 as / s = 50.8. The exposure time is 1/50, 8 second.