BMPCC How to quickly set the shutter angle?

This question should start from the principle of movie cameras. The shutter of a movie camera, professionally called a "fender", is the reflector used by the camera for framing. The shutter is a circular lens with an opening angle. When shooting, it cooperates with the camera's gripper and fixed pin. The movement rotates at high speed. When the film grabbing claw grabs the film, the leaf plate just blocks the film door and reflects the light to the viewfinder. The photographer can see the scene outside the lens; when the film fixing pin fixes the film at the film door, The opening angle of the fender just passes the film gate, and the light is projected onto the film through the opening angle of the fender, and the film is exposed. The shutter is usually semicircular, and the angle when it opens is 180 degrees. The shutter speed and exposure are determined by the intensity of light passing through the lens and the time it takes for the film to be exposed: exposure = light intensity × time. Therefore, the exposure obtained by doubling the photosensitive time is equal to doubling the intensity of light. The intensity of light passing through the lens is determined by the aperture size of the lens. When the aperture of the lens is reduced by one stop, if a certain exposure still needs to be maintained If the amount is too high, you need to double the exposure time of the film. The film's film speed (frame rate) is 24 frames per second. The film exposure time of a camera with a shutter opening angle of 180 degrees is 1/24X1/2=1/48 seconds (approximately equal to 1/50 seconds). For cameras with different frame rates and shutter opening angles, the shutter speed can be calculated by the following formula, that is, shutter speed (exposure time) = 1/frames per second X shutter opening angle/360. A camera equipped with an adjustable shutter can adjust the shutter opening angle to change the shutter speed. When the shutter opening angle is reduced, the exposure time is reduced, that is, the shutter speed is higher. For example, for a shutter with an opening angle of 90 degrees and a rotation speed of 24 frames per second, the shutter speed is calculated by the above formula: 1/24X90/360=1/96, which is approximately 1/100 second. When the shutter speed is faster, a wider aperture can be used to achieve a shallower depth of field when shooting outdoors. The shutter of modern digital cameras is completely programmed by electronic circuits. The opening and closing frequency control settings are very flexible. With aperture, ISO sensitivity (called "gain" on the camera) and density filters, it can be adapted to various occasions to achieve complex results. shooting effect. Digital cameras often have shutter angle adjustments, but they are actually only set up to suit photographers who are used to using movie cameras.

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