Movie projector
A film projector or motion picture projector serves to a movie camera to image recorded stripes on a screen project . Normally 24 still images are shown per second . Since 24 light-dark changes would be perceived by the human eye as an annoying flicker, each image in the state is additionally interrupted by the rotating screen , whereby 48 changes are generated for the eye, i. H. each film frame is shown twice.
There are also projectors with 18 (for Super 8 films) or 25 frames per second (for TV films). Most silent films should be shown at 16 to 22 frames / s, as they were shot at this speed, otherwise movements appear in time-lapse . For scientific purposes there are projectors with image frequencies that can be varied within wide limits . Even municipal cinemas are mostly equipped with projectors with variable speed.
Due to the network frequency of 50 Hz common in German-speaking countries, television works with 50 fields per second, i.e. H. with a frame rate of 25 Hz. To avoid interference , movies are therefore broadcast on television with 25 Hz instead of 24 Hz, which shortens the running time by 4%. A film of 100 minutes (cinema) duration runs on television or on video for only 96 minutes.
For around a century, film projectors were without competition. Since the year 2000, among other things, for reasons of savings, "cinema films" have increasingly been produced and distributed digitally, which is accompanied by a conversion to digital film projection .
Components
The most important elements of a movie projector are
- the film drive (for example a Maltese cross lock in connection with a pulley or a gripper), which transports the film in the dark phase so that it can be projected in the light phase as long as possible. The film runs in a so-called film path, where it is guided lengthways, crossways and along the optical axis (see the nomenclature of narrower film technology ).
- the rotating aperture (sector disk), which interrupts the light beam while the film is being transported, and then again in the middle of the moment the film image is shown (increasing the flicker frequency)
- the light source: for 35 mm film , as it is normally played in cinemas, it used to be carbon arc lamps , today it is xenon arc lamps with an electrical output of between 900 watts and 10 kW (the largest common xenon lamps have 7000 W). In the case of 16 mm films, xenon lamps and halogen bulbs are sometimes used. 8 mm film projectors usually have halogen lamps. The first 35 mm film projectors for home use also used normal incandescent lamps or even kerosene lamps.
- a condenser that projects the light source onto the aperture plane of the lens ,
- the image masks (image windows) for the various image or projection formats so that the soundtrack and perforation are not also visible on the screen.
- the light flap, a metal panel between the film and the lamp, which closes automatically if the film breaks or the projector stops, protecting the film from the heat of the lamp (if the flap jams, the film melts); and is otherwise operated by the presenter in order to fade out parts of the film not intended for the presentation, such as the start tape. Other light flaps can close the projection window (so that the film from the no longer active projector is no longer projected onto the screen when fading over).
- the projection lens to project the image sharp or rectified and in the right size onto the screen
- the sound device for optical sound or magnetic sound that scans the soundtracks of the film
- To the film drive
As a current development, the mechanisms are being replaced by a stepper motor in conjunction with a pulley. Advantages are supposedly improved image stability , better light utilization through shorter switching times (time that is needed to transport the film by one step) and less wear and tear on the film and equipment.
There are also methods in which the film is not deposited but moved continuously. The light of the image reaches the lens via a system of prisms or mirrors rotating synchronously with the movement of the film. The Ernst Leitz company built the Mechau projector based on this principle . The method is also used in small viewing devices that image on a ground glass.
- Wide screen process
Widescreen films are masked; This means that only part of the maximum possible screen format is shown during projection. The American widescreen with an aspect ratio of 1: 1.85 and the European widescreen with an aspect ratio of 1: 1.66 are common. This is to be distinguished from the Cinemascope process, in which the film image is distorted during recording: so that more information can be recorded in terms of width, the image is compressed horizontally by a cylindrical lens. To show such films, the projector must be equipped with an anamorphic lens that corrects the image. The aspect ratio of the projected corrected image is 1: 2.35 for light tone copies. Slidable matt black “bezels” limit the image so that there are no fuzzy edges to be seen on the canvas.
Film guidance in the projector
The film channel, i.e. the winding path that the film travels within the projector, is equipped with several rollers and toothed rollers. First of all, by means of lateral bars, they ensure that the film is exactly in the middle in the direction of travel. A first sprocket roller (pre-winding roller) pulls the film from the supply spool, which is located in the upper fire protection drum . In the case of spool towers and plate operation, separate motors ensure continuous film feed. This is followed by the first, upper film loop as a transition from the continuous movement to the stopping-and-transporting by the switching roller .
Above this loop is the film tear switch, which is lifted as soon as the film jams between the pre-winding roll and the film channel. This then switches off the drive motor and sound lamp, and a light protection flap closes in front of the picture window. As previously flammable nitro films were used, one was fire switch is provided which has been preloaded by a separate nitro film loop. If the passing copy caught fire, this loop burned as well and set off the fire switch. The same consequences occurred here as with the film break switch; In addition, drop flaps were triggered in front of the projection and viewing openings in the demonstration booth.
In the film channel, which can be opened for insertion (film door or slide), the film is guided between the film web with velvet support and two pressure skids . A suitable image section is illuminated by the lamp through the image window of the mask and projected by the lens clamped in the lens carrier.
For cooling u. a. of the film in the film channel there is partially a cooling water connection with inlet and outlet. As an alternative or in addition to water cooling , some versions have a heat protection filter arranged between the lamp and the picture window or compressed air cooling of the picture window.
After the film has run through the carriage, where it was projected frame by frame, another film loop follows, then another toothed roller (rewind roller), which sets it in continuous motion again. To insert a film, the presenter adheres to the “principle of the longest way”.
The light sound device is arranged after the lower loop . The film passes first through a brake roller with rubber pressure roller and reaches the capstan on which the sound track from the exciter lamp (later also laser earlier bulb) illuminated by slit optics and is scanned by a light receiver (formerly by a photocell , and later by photodiodes ). The clay reel is connected to a flywheel and is only set in rotation by the film that wraps around it. The film then runs over a pendulum roller, which ensures that the film is taut in the sound device, and is fed into the lower fire protection drum via the toothed rewind roller, where the lower pressure roller prevents the perforation from jumping out. The driven lower reel shaft winds the film on a reel (catch reel, empty reel) or a bobby (a small reel core; formerly made of wood, now made of plastic).
All toothed rollers and the gripper system (pulley) are synchronously coupled with one another. The pulley, slide and image mask can be moved vertically as a whole in order to be able to adjust the image position of the film. Through this Frame adjustment the presenter can - if the film is loaded incorrectly - ensure that the entire film frame, but not the lying between two images frame line is shown. The runners pressure of the slide can be adjusted, on the one hand to compensate for mechanical differences in the film material (e.g. waves, kinks, splices) and on the other hand to securely fix the image during its standstill. The position of the rotating diaphragm must be adjusted in relation to the pulley so that it only releases the beam path when the film comes to a standstill. Further wings on it increase the light-dark frequency so much that no flickering is perceived.
Before inserting the film, the manual drive is operated until the switching roller is just in the rest position. The film is now inserted in such a way that there is exactly one single image in the image window. Since the projector needs a certain amount of time to start up, an image from the start tape is usually not positioned in the image window, but rather a film image. In order to ensure that there is no shift in the position of the picture between the inserted picture and the first actual picture of the act (there is usually a black band without a visible picture line immediately in front of the first actual picture), the presenter should carry out a corresponding visual inspection. This can e.g. This can be done, for example, by running the film by hand over an old pre- / post-winding roller on which there are markings for the image line (see illustration of the toothed rollers).
There are 16 ways to load 35mm film. This number of combinations results from multiplication
- 2 options for the direction of travel (start → end or end → start)
- 2 possibilities for the position of the sound track (or the side position of the picture)
- 4 possibilities for inserting a single picture in the picture window (corresponding to the 4 perforations per picture).
Of these 16 possibilities, only one leads directly to a correct projection, with three further options a correction by means of the image line adjustment is still possible. In the remaining 12 cases, however, the screening must be interrupted and the film reloaded. The film is inserted correctly if
- the beginning of the film runs in the direction of travel into the projector ("heads down")
- the audio track is on the right in the viewing direction of the screen
- exactly one image is inserted into the image window
To protect the film, all rollers (and other parts that come or may come into contact with it, such as the film channel, but also the film tear switch) are designed so that only the perforation comes into direct contact with these parts. Therefore, there are corresponding depressions in the area of the actual image (see e.g. illustration of the toothed rollers).
In the idle state, the film channel and all pressure rollers should always be open. If this is not taken into account, flat spots can form, especially on the rubber pressure roller of the sound device, which cause malfunctions.
Movie tour to the projector
The management of the film within a projector is always the same. There are differences in the way the film gets in and out of the projector.
Crossfade operation
Films are traditionally delivered in "files". This name has been adopted from the theater. One act is up to 2000 feet long (around 600 meters), which corresponds to 22 minutes of running time. In the past, the film rolls were packed in tin cans or flat cardboard boxes, today mostly in plastic round boxes. The division of the film into several acts was previously necessary because the burning time of the coals of a coal arc lamp was limited to about 45 minutes. A normal length (feature) film of 90 minutes could not have been shown without interruption. It also made transport easier (if a 90-minute film were wound onto a single spool, it would have a diameter of over a meter).
The files are not delivered on spools, but wound on the aforementioned bobbies.
Usually, every act has a colored protective film at the beginning and end, an allonge , which enables the presenter to immediately recognize which act it is and whether it is "at the beginning" or "at the end" - depending on whether Beginning or end of the act are on the outside. However, it is advisable, as a demonstrator, not to rely on the everything, but to carry out a visual inspection.
The allonge is followed by the so-called start tape , also called "blank film" (because the film does not contain any individual images). Then the film begins, which contains images and the soundtrack. The soundtrack is offset by a few images “before” the actual projected image, as scanning, amplification, transmission to the loudspeaker and sound propagation to the audience's ears require a certain amount of time and otherwise there would be asynchrony between lip movements and the words heard.
If there are two projectors (called "a pair"), they are mirror-inverted (technically a left and a right machine, depending on whether the film is transported on the left or right side of the machine when viewed in the projection direction) so that the presenter can can operate both machines from the same intermediate aisle.
For the screening, the files must be wound "at the beginning", the beginning of the film must be on the outside of the roll. At the end of the projection, however, the beginning is inside the film roll. The reel must therefore be rewound before the next performance so that the beginning is on the outside again.
If the film is removed directly from the rewind after the last screening and placed directly in the transport can (with the help of a take-up reel that can be dismantled), the beginning is inside again. A projectionist must therefore make sure before the performance whether the roles are beginning on the outside.
With copies that are played back very often, the perforation suffers and can fray and tear. If the film does not run around the deflection spools in the projection apparatus, the film can tear there, which naturally leads to chaos in the projection room. Usually the film is unwound for a few more meters and fills the space before the film break switch stops the film transport. Then, in order to save time, the twisted film is cut off and the film is reinserted in the projector. The newly inserted film is temporarily wound onto the take-up roll until the friction “takes it with it” and winds it up again. The piece of film unwound in the room must later be re-installed in the film when it is rolled over. In order to avoid such film tears, the perforation of old copies must be checked.
The art of the presenter also consists in starting the projector in good time at the end of an act with the following act and switching image and sound so that the audience does not notice a transition. To help it, at the end of a file , so-called file change marks , also known as “fade marks”, are copied or scratched into the upper right corner of the picture. When the first mark appears, the presenter starts the second projector (light and drive), with the second mark there is a cross-fade (when the second projector starts, a flap of light falls between the lens and the projection window of the first projector and prevents the images from mixing or the first projector "idle" unnecessarily brightens the projected image of the second projector). The two characters are necessary because the projector needs a certain amount of time to start up (for details on the timing, see there ). Because the files suffer from frequent demonstrations, it is advisable to use your own dissolve characters e.g. B. from circuit board tape (which can be removed without leaving any residue). Experienced demonstrators can sometimes tell when the second projector should be started by the diameter of the supply roll.
There are projectors that relieve the demonstrator of manual cross-fading. For this purpose, small pieces of metal self-adhesive tape are attached to the film. A scanner reacts to this and takes over the otherwise manual work steps, i.e. starting the second projector and cross-fading. With three or even four projectors, you can run a program for up to an hour automatically in this way. Today, all acts of a film are typically linked (i.e. glued together) before showing and shown using one of the methods described below.
Coil operation
The individual files of the film copy are glued ("coupled") one behind the other (without allonge, black film and starting tape) and wound onto a reel. The beginning of the film is outside. The "upper" or film-forming reel is called the supply reel , the reel onto which the film is wound after projection is called the take-up reel , catch reel or empty reel . If the film is to be shown again after a projection, it must first be rewound from the take-up reel onto the supply reel. The coupling takes place on a rewinding table , a construction with two small, nude-sized plates (often still operated with a hand crank) and a gluing press next to it.
There are projectors whose unwinding and winding frictions are vertically on top of each other, others where both coils are attached to the lamp house next to each other. Finally, there are coil towers that are right next to the projector or some distance away. Since the mass of such a reel with a full film is too great to be moved by the first sprocket of the projector without damaging the perforation, it has its own motor that adjusts its speed depending on the degree of unwinding.
Plate operation
For the non-stop showing of cinema films with a projector, in addition to the coil tower, so-called plate systems have also been available since the late 1960s, in which the film lies horizontally on large plate levels. For the screening, the beginning of the film is brought out of the middle of the roll and wound up again on another level. The endless plate is a further development for special cases.
Control and automation in the projection room
See separate article matrix machine .
See also
Current and former manufacturers of cinema projectors
| Manufacturer | country | place | Further information | Production active / discontinued |
|---|---|---|---|---|
| Sweden | License from Ernemann-Zeiss-Ikon | set | ||
| AE-G. | Germany | set | ||
| Askania | Germany | Berlin-Friedenau | set | |
| Bartling | Germany | set | ||
|
Eugen Bauer GmbH ("Kino-Bauer") |
Germany | Stuttgart-Untertürkheim | Founded in 1905 by Eugen Bauer, taken over by Bosch in 1932 ("Bosch Photo Cinema") |
set |
| Buderus | Germany | set | ||
| Century | United States | active | ||
| Christie | Canada | active | ||
| Cinemeccanica | Italy | active | ||
| Cinetecnica Firenze | Italy | Paolo Veronese | active | |
| Diksi (later Dixi) | Switzerland | Le Locle | License from Ernemann-Zeiss-Ikon, 35 mm | set |
| Ditmar | Austria | set | ||
| ERKO | Germany | Berlin | Erdmann & Korth | set |
| Ertel | Germany | set | ||
| Ernemann | Germany | Dresden, now Kiel | originally Heinrich Ernemann | active |
| Friedl-Chaloupka | Austria | set | ||
| Frieseke & Hoepfner | Germany | Erlangen-Bruck | set | |
| Fumeo | Italy | active | ||
| Léon Gaumont | France | set | ||
| Harbin Film Machinery Plant | China | active | ||
| IC-A. | Germany | set | ||
| Kalee | United Kingdom | set | ||
| Kunert | Germany | set | ||
| Cinema sound | Germany | Germering | Inventor of the horizontal film plate, acquisition of the Philips FP 20 patents and production 1972. | active |
| Leitz | Germany | set | ||
| Lehmann & Knetsch | Germany | set | ||
| Liesegang | Germany | Dusseldorf | set | |
| Marin | France | active | ||
| Messter | Germany | set | ||
| Meopta | Czech Republic | Přerov | set | |
| Monee | India | Bangalore | active | |
| National | United States | ? | ||
| Johannes Nitzsche | Germany | Leipzig | set | |
| OFAG | Germany | set | ||
| PAGU | Germany | set | ||
| Pathé frères | France | set | ||
| Peck & Kerkhof | Germany | set | ||
| Philips Cinema | Netherlands | Eindhoven | License / replica Nitzsche Castor and Nitzsche Saxonia |
set |
| Prevost | Italy | active | ||
| PROMAG | Germany | set | ||
| Rien & Beckmann | Germany | set | ||
| Skull & Co. | Germany | set | ||
| Mould | Germany | set | ||
| Tailor and son | Germany | set | ||
| Seischab & Co. | Germany | set | ||
| Siemens & Halske | Germany | set | ||
| simplex | United States | active | ||
| Stachow | Germany | set | ||
| Strong | United States | active | ||
| VEB Carl Zeiss Jena | Germany | Jena | set | |
| VEB Pentacon | GDR | Dresden | Successor to Zeiss Ikon | set |
| Wassmann | Spain | Madrid | active |
Film screening on board aircraft
Projectors have been installed in commercial aircraft for in-flight entertainment , i.e. to entertain passengers on air travel . On April 26, 1970, a film projected on a screen was shown for the first time at Lufthansa on a long-haul route . As early as 1989, however, the first screens were installed, which replaced film projection on canvas.
literature
- Herbert Tümmel: German motion picture projectors. Deutsche Kinemathek Foundation, Berlin 1986
Web links
Individual evidence
- ↑ Pair. Lexicon of Film Terms, University of Kiel , February 18, 2013, accessed on July 1, 2018 .
- ↑ Conversation Above the Clouds , Die Welt, February 12, 2007