Post projection is one of the film projectors included in the film installation , designed for continuous film screening of films consisting of several parts [1] . The duration of one standard part of a film made on a 35 mm film can not exceed 10 minutes , therefore, when showing full-length films lasting 1-2 hours , several movie projectors are used, each of which charges one part of the film copy . At the moment the part ends in one projector, the next one starts with such a calculation as to make the transition between the parts invisible on the screen. This is called post-to-post transition. During the demonstration of the next part, the projectionist manages to charge the film to the next post and prepare it for work. Until the late 1990s, the presence of two or more posts in cinemas was mandatory.
Content
Film Continuity
For the first time, several posts of film projection began to be used in large European and American cinemas in 1914 , excluding the stop of the session every 15 minutes at a “ silent ” projection frequency of 16 frames per second [2] . At this point, automation did not exist, and for the exact transition from post to post, only special marking of the film-copy grade was used , which facilitates the charging of each part and the exact start of the next post, performed manually. So, to indicate the moment the next projector starts, to precisely align the beginning of the next part with the end of the previous part in the upper right corner of the frame of each part, a round marker (signal “motor”) appears for a split second, visible 8 seconds before the end of the part. In widescreen movies, the mark looks like an oval due to anamorphic effects . Having seen it on the screen, the projectionist must start the mechanism of the next post so that he can accelerate to the rated speed. Then, one second before the beginning of the final record of the part, the same “transition” marker appears: this is a signal for opening the light damper of the second post and closing the damper of the first.
Thus, at the moment the image of the previous part ends, the image of the next part already appears in the frame window of the running post, and the projector mechanism operates at a nominal speed. Acceleration of the mechanism is especially important for high-quality reproduction of a phonogram that sounds distorted until the sound-absorbing drum has entered the steady-state rotation mode. The starting record of each part is also marked so that at the moment the stable operation of the mechanism begins, the initial frames of the part fall into the frame window. Thanks to the marking, a segment of the film passing in the tape drive during acceleration corresponds to the distance between the markers at the end of the previous part. This technology allows you to bring the accuracy of the transition to 1-2 seconds, which is quite acceptable for a normal display. In accordance with international standards SMPTE 301M-1999 and 55-2000, the duration of each of the two signals should be 4 photocopy frames [3] [4] . In most cinemas, 3 movie projection posts were installed, but in large movie centers there could be up to 4 posts. A two-post film installation was used in small cinema halls, not allowing to keep one of the projectors in reserve in case of breakdown.
Automated film screening
To simplify the work of projectionists and improve the quality of film screening from the end of the 1940s , automated control of all movie projection posts has been used, which allows for accurate transitions between parts, invisible to viewers. To automate the transitions, in addition to the usual marking, a special conductive foil is fixed on the perforations in certain places of each part of the film, which drives the automation of the transition from the corresponding sensor [5] . At the same time, the next post starts automatically, and after acceleration, the flap automatically opens, opening the frame window, and the flap of the previous post closes. From a projectionist in an automated display, exact observance of the marking when charging each part and competent control of the control device is required.
In the cinemas of the USSR, the AKP-6 device and its modifications were used to automate the cinema display. In addition to transitions from post to post, the device controlled the screen curtain drive and the light in the cinema [6] .
Matching post images
When installing film projectors in a cinema equipment room, it is important to adjust the position of images of different posts on the screen [7] . Images from different movie projectors should match as closely as possible, otherwise the transition from post to post will be noticeable to viewers. In addition, when designing the hardware, the need to ensure that the lenses of all posts are located as close as possible to ensure the optical axis of the projectors is perpendicular to the screen. This minimizes the distortion that occurs with oblique projection.
Reducing the number of transitions
Despite all the tricks, the transitions from post to post are still noticeable and complicate the work of projectionists [1] . Therefore, in large cinemas, to reduce their number, several parts are glued together into one, since the design of most film projectors allows you to charge rolls that exceed the standard length of 300 meters. So, the Soviet film projector 23KPK allowed to charge up to 600 meters, obtained by gluing two parts. However, it is impossible to show a full-length film 2500-2700 meters long in one piece without special technologies. In the early 1970s, film projectors with large-capacity reels up to 4000 meters appeared. However, such systems are not widespread due to the inconvenience accompanying work with large rolls, the weight of which reached 70 kilograms [8] .
Rewindless devices have become an effective alternative to multi-post movie installations, allowing you to charge a film glued into a large roll, placed horizontally on a special platter , into individual types of film projectors [9] [5] . This technology, combined with xenon lamps , the continuous operation time of which, unlike a carbon arc, is unlimited, allows the installation of a single post in a cinema. Film projectors of the IMAX system work only on this technology because of the large weight and dimensions of film copies, so until recently there were restrictions on the maximum duration of films in IMAX format.
Digital Screening
Modern digital film projectors allow you to show movies of any duration continuously. Therefore, the concept of "post" in digital cinema is outdated. More than one projector can be installed in a digital cinema hardware, but this is used for other purposes. For example, with two-projection 3D technology or to reserve and reduce the intensity of operation of each digital movie projector, using them in turn for different sessions.
See also
- Part of the film
- Movie installation
- Platter
Notes
- ↑ 1 2 Photokinotechnics, 1981 , p. 420.
- ↑ General History of Cinema, 1958 , p. nineteen.
- ↑ Motion-Picture Film - Theater Projection Leader, Trailer and Cue Marks . SMPTE 301-1999 . Thomson Reuters. Date of treatment April 4, 2015.
- ↑ Motion-Picture Film - 35 and 16-mm Television Release Prints - Leaders and Cue Marks . SMPTE 55-2000 . Thomson Reuters. Date of treatment April 4, 2015.
- ↑ 1 2 Voropaev Alexey. Tips of professionals . "Projectionist". Date of treatment April 4, 2015.
- ↑ Handbook of Cinema Mechanics, 1988 , p. 398.
- ↑ High-tech screen area of a modern cinema hall (inaccessible link) . Film production workshop. Date of treatment April 4, 2015. Archived April 11, 2015.
- ↑ Technique of Film and Television, 1973 , p. 73.
- ↑ Rewindless devices, 2005 , p. 6.
Literature
- E.A. Iophis . Photokinotechnics / I. Yu. Shebalin. - M.,: "Soviet Encyclopedia", 1981. - S. 420. - 447 p.
- Yu. P. Cherkasov. Power distribution devices and auxiliary equipment // Handbook of projection mechanics. - 2nd ed .. - M .: Higher School, 1988. - 415 p. - ISBN 5-06-001188-7 .
- Georges Sadoul . The general history of cinema / B.P. Dolynin. - M.,: “Art”, 1958. - T. 2. - 523 p.
- V.D. Gribov, N.N. Usachev. Rewindless devices / N. N. Kalinina. - SPb.,: Editorial and Publishing Department of SPbSUKiT , 2005. - 42 p.
- V. B. Munkin. Automation of film screening (Russian) // " Technique of cinema and television ": magazine. - 1973. - No. 2 . - S. 81-84 . - ISSN 0040-2249 .