Cross-country skiing facility
In cinema operations , cross-country facilities are devices that enable the playback of a film with only one film projector without pauses between the individual acts .
prehistory
In the early days of cinema, films were only a few minutes long and were shown by traveling showmen, which changed with the advent of fixed movie theaters and the electrification of cities. Film projectors have now been permanently installed in movie theaters and thus enabled a significantly improved presentation quality. At that time, however, the duration of the demonstration on a projector was strictly limited for various reasons: The burned-out electrodes of the carbon arc lamps had to be regularly replaced with new ones, and the celluloid film used at the time was at high risk of fire and was therefore placed in fire protection drums on the projector , which were not due to fire protection reasons took more than about 20 minutes of film.
For these reasons, it was necessary to align two or more projectors to the same screen in order to continuously show longer films and to show the film alternately on them in cross-fading mode. This approach could only be abandoned when security film caught on - in Europe at the beginning of the 1950s - and carbon arc lamps were replaced by xenon gas discharge lamps , which happened around ten years later.
Now it was also possible to play back longer sequences of a film by coupling several acts from a single larger reel and, for example, only fade between the projectors every hour when using reels with a capacity of 1800 m of film. However, since 1800 m spools already have a diameter of more than 60 cm, they represent the upper limit for the "classic" presentation on the film projector (unwinding reel above the projector drive, winding reel below) and a continuous showing of longer films is not possible.
Coil tower / sidewinder
The simplest possibility of a cross-country skiing facility is the so-called coil tower, in which two coils with an even larger capacity are attached to an additional frame that is set up next to or behind the film projector. Typically, the capacity of tower reels is 4000 or 5000 m of normal film , i.e. a playing time of around two and a half or a good three hours. The film is fed from one reel ( supply reel ) to the projector and, after passing through the projector drive, back to the reel tower, where it is rewound on the second reel ( take-up or catch reel ) - depending on how the reel tower is set up, possibly via pulleys .
When coupling, the film must be prepared in such a way that the beginning of the film is on the outside of the spool for showing; However, after the replay it is at the core of the second reel, and the film must be rewound before it can be shown again. For the coupling and decoupling of a film, most reel towers offer the possibility of attaching plug-in reels in such a way that individual film files can be wound up and unwound from or on one or both reels.
Since the mass of a complete film is in the double-digit kilogram range, it is too large to be moved by the first sprocket of the projector without damaging the perforation of the film. For this reason, spool towers have their own drive not only on the winding, but also on the unwinding spool, which adjusts the speed of rotation depending on the degree of unwinding.
In addition to coil towers with vertically stacked coils, there are also those in which the coils are arranged horizontally next to one another or opposite one another, the latter is also called "sidewinder". There are also projectors in which such a sidewinder is integrated in the foot, with the film being fed into the drive from above via pulleys from the unwinding reel.
Film platter system
The rewinding of the film before or after each performance is not only expensive, but also leads to damage to the film material when the individual layers rub film on the coil to each other or at the completion of Umrollvorgangs on table or floor dirtied be. Therefore, a search was made for ways to lead the beginning of the film out of the center of the roll in order to enable several screenings in a row without loss of time and material damage caused by rewinding.
In the 1960s, the Bad Saulgau projectionist Willi Burth developed the so-called “non-rewind film plate”, in which the film roll is placed horizontally on a plate with a diameter of about 1.5 m. This has the advantage that a flank of the spool can be omitted and the film roll is accessible from above. The film is wound onto a metal or plastic ring that is removed before the performance. A special plug-in unit is now placed in the middle of the film roll and the beginning of the film is guided through it at an angle upwards and over pulleys to the projector. After passing through this, the film is fed back to the plate system and again wound onto a ring on a second plate level. Thus, the beginning of the film is always inside the film roll, a new screening is possible with practically no time delay. In addition, the process is more gentle on the film than reel operation, since - with proper operation - the image and sound of the film are always guided and thus cannot be scratched.
The plate system, patented by Burth in 1969, was sold by the film technology manufacturer Kinoton and improved over the years. In addition, plate systems from other manufacturers such as Ernemann or Cinemeccanica now also exist . A plate system typically has three or five plate levels. Two of these levels are used for a film showing (one as an unwinding, the other as a winding level), on the third level another film can be mounted or dismantled at the same time using a rewinding table , in systems with five levels a second film can be shown in parallel . Burth received several awards for his invention, including in 1987 the Scientific and Engineering Award of the Academy of Motion Picture Arts and Sciences, known as the "Technology Oscar" .
The insertion unit controls the speed of the unwinding plate via a fork swinging to the right and left (or a comparable sensor installation) on the film holder. There are different systems: With the Kinoton type there are switches at the stops of this fork, which increase or decrease the speed of the platter depending on the transport speed to the projector, Cinemeccanica platters use a speed control via a potentiometer , which is directly connected to the fork connected is.
In new systems, the speed and the film tension of the winding plate are controlled by a microprocessor ; in older systems, this regulation takes place via movable pulleys, which accelerate the plate if the film is fed in faster than it is wound up and, in the opposite case, brake it. The tension should be set so firmly that the completely wound film can be lifted off the plate completely after the end has been fixed with adhesive tape and can be set up vertically for storage.
Endless plate
If a film is often shown one after the other at short intervals, the re-inserting of the film over all the pulleys and into the projector drive, which is necessary with the plate system after each showing, is time-consuming. The so-called endless plate was developed for such cases: the film is mounted on a "normal" plate level and wound up on a special plate level during the first screening, after which the beginning and end are glued together and the film is shown as an endless loop.
Since the film is removed from the inside (i.e. where the ring radius is small and therefore the speed of rotation would have to be higher), but wound up outside with a large radius (and therefore lower speed), it cannot simply be wound up in a spiral. It is therefore wound up as a polygon and shaped in a star shape with several "spikes" using a transport mechanism. In this way the circumference of the roll is the same inside and outside and it can be wound and unwound at the same speed. Since the system is quite complex, it is not easy to use and can easily damage the film.
Based on the same considerations, an endless bobbin tower called "Loopmatic" was developed in the USA, which, however, never achieved large numbers and has apparently never been used in Europe.
Individual evidence
- ↑ Klaus Kramer: Identify and discard nitrate films. Retrieved April 10, 2011 .
- ↑ Brochure Ernemann E 15-5000. (PDF 152 kB) Ernemann CineTec GmbH, accessed on April 10, 2011 .
- ^ Willi Burth - A lifetime of cinema. Willi Burth-Museum Ravensburg, accessed on April 10, 2011 .
- ↑ Kinoton film plate systems. (No longer available online.) Kinoton GmbH, archived from the original on April 27, 2011 ; Retrieved April 10, 2011 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ^ Film plate: Ernemann. Ernemann CineTec GmbH, accessed on April 10, 2011 .
- ↑ Cinemeccanica CNR 3-35N. (No longer available online.) CINEMECCANICA SpA, archived from the original on May 3, 2011 ; accessed on April 10, 2011 (English). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Film-Tech Forums: Anyone ever seen a XeTron Loop-Matic? Retrieved April 10, 2011 .
- ↑ User album: Loopmatic endless coil tower. (No longer available online.) Projection Forum, archived from the original on December 6, 2015 ; Retrieved April 10, 2011 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
Web links
Private homepage with an overview of various types of cross-country skiing facilities