Optical printer

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An optical printer with two projector heads.
You can see the image window (A) of the first projector; a lens (B) projecting the image from A onto the image window (C) of the second projector; the lens (D) of the camera; the viewfinder (E) of the camera; also the locking control (F) and the control electronics (G) in the heavy foot of the device.

An optical printer (also " optical bank ", from English optical printer for optical printer ) is a device that is used to create optical film effects , for copying in film titles, optical copying , format conversion (e.g. from 35 mm to 16 mm or vice versa) and the restoration of old film material is used.

construction

An optical printer essentially consists of one or more film projectors , a number of semitransparent mirrors depending on the number of projectors, optics for aerial image recording , and a camera that is mounted opposite the projectors. The transport of projectors and cameras is linked to one another, but can also be carried out independently. The camera can be moved along the optical axis, which means that it can record partial sections of the projected film to a limited extent.

All components of an optical printer must be located exactly on the same optical axis . If two films are to be recorded at the same time, two projectors are required, one of which is mounted at an angle of 90 ° to the main optical axis. A semi-transparent mirror is positioned at an angle of 45 ° in the beam path and deflects the image from the second projector so that it is projected congruently with the image from the first.

All existing projectors focus their image in the same size on the center plane of an aerial image lens, a combination of two equally powerful magnifying lenses. The camera also focuses on this plane. The image in the center of the system is virtual; it can only be recorded by the camera if its film plane is at the same distance from the central plane as the film plane of the projectors, and if the projector and camera have lenses of the same focal length. The method has the advantage that neither light losses nor surface disturbances occur as with projection onto a ground glass. In addition, there is enough space in front of and behind the aerial image lens for color filters, effect glasses and panels that are required for the various corrections and effects.

The camera and projectors are equipped for “bi-pack”: their film channel is set up so that two film strips run through at the same time. On one film you can see e.g. E.g. an actor who is supposed to fly, on the other film the actor is completely white and everything else is black. So this second strip of film is a mask. It is produced optically and with the help of the copier and is essential for multiple exposures. After the first combination of film strips has been filmed, the film is rewound in the camera. A second film, e.g. B. with a moving sky, another mask, which this time covers the actor and leaves everything else free (i.e. a negative of the first mask), is inserted into the projector and recorded again (if there are two projectors, the recording can be done in a single Step). After development, the camera negative shows the flying actor in front of the sky.

Optical printers are manufactured with the highest precision so that the effects created in this way are convincing and not noticeable due to small wobbles or other impurities. In addition to normal film transport, locking grippers ensure a precise image position in the order of 1/2000 of the image height.

Frequently used optical effects are up and fade , slow-motion , time-lapse and mat shots . More elaborate shots can contain dozens of such elements in a scene. Ideally, the film audience should never notice that an optical printer was at work. However, the difference in even for laymen film grain visible, if at the end of a longer setting the clamp part begins with the transition, because for economic reasons was particularly in the 1950s and later in television series of Optical Printer only for the part of the scenes used who needed an effect. To mitigate this difference, particularly fine-grained films were finally used for the copying work, or the scenes intended for complex copying and trick work were shot in a larger film format .

development

The first simple optical printers were built in the early 1920s. The American film technician Linwood G. Dunn expanded the concept in the 1930s, for which he received an Oscar in 1949 . The further development lasted until the 1980s, when the printers were controlled by mini-computers . Optical printers experienced their highest expansion stage at " Industrial Light & Magic " (ILM), the company of George Lucas . From 1976, a "Quad" printer (an optical printer with 4 projectors) was used there for the extensive and complex special effects of the Star Wars series. From the end of the 1970s onwards, a series of films were made that celebrated real effects orgies, all of which were made on the optical printer: the three Star Wars films, the Superman films, Disney's “ The Black Hole ”, “ Flash Gordon ” and others.

In the late 1980s, digital effects began to replace optical effects. The switch to digital effects has been almost complete since the mid-1990s. Since then, optical printers have mostly only been used by individual artists who work exclusively with film. They were particularly useful there for making copies of hand-painted or physically altered films.

literature

  • Dirk Mathey (Ed.): Making of… Volume 2. Rowohlt Tb., Reinbek 1998, ISBN 3-499-60575-9
  • Rainer Rother (Ed.): Sachlexikon Film . Rowohlt, Reinbek 1997, ISBN 3-499-16515-5 , p. 223

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