Magazine article American Cinematographer

Cinema Workshop

Magazine article American Cinematographer

Cinema Workshop

Article excerpt

SHUTTERS IV

During the years I spent with the Arriflex Corporation, I must have been asked at least a million questions concerning every imaginable technical aspect of the Arri line of cameras. Just when I thought I had heard them all, someone would come up with an esoteric question from left field: "What kind of filter do you recommend for filming a seance?", "My Arri S just fell into a vat of chocolate, what should I do?" (Ans: Dark chocolate, open up two stops), "I'm going to a country where the current is 287 volts at 42Vz cycles per second, what kind of sync motor should I use?"

Obviously, most of these questions were unique and hopefully I had to answer each only once. However, there were several questions that were veritable standards. The most popular was: "How come the Arri mirror shutter has a black painted stripe in the middle of the mirror?" A reasonable question. After all, the main purpose of the mirror is to reflect the brightest image possible onto the ground glass, so why would you reduce the amount of reflecting surface by painting part of the mirror black? (see FIGURE I)

When the mirror reflex shutter was first introduced, it caused quite a reaction in the film industry. Almost everyone is now familiar with the obvious attributes. However, there is one drawback that is now taken for granted, FLICKER. Cameramen were not accustomed to the image turning on and off while they were attempting to compose a frame. Arnold & Richter decided it would be wise to reduce this flicker effect to a minimum, as some cameramen were bound to find it objectionable. The obvious way to reduce flicker would be to decrease the dark or off period of the shutter. This was impractical because it would mean a smaller shutter opening and less light for the film. The less obvious way would be to reduce the perceived flicker by increasing the effective flicker rate. This cure is based on a very important phenomenon of motion pictures, the critical flicker frequency.

Early experimenters in motion pictures found that, due to the so called "persistance of vision", (the eye/brain holds an image for a short instance after that image is removed) motion could be perceived from a series of still pictures. They established that these pictures had to be flashed at a rate of approximately 16 a second or faster for the sensation of relatively smooth motion. …

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