Movie projector

A film projector or motion picture projector is used to project the recorded with a movie camera filmstrips onto a screen. This 24 still images are shown per second normally. Since 24 light-dark change would be perceived by the human eye as annoying flicker, each image is also interrupted in the state of the rotary shutter, making 48 changes are generated for the eye, that is, each film frame is shown twice.

There are also projectors with 18 ( in Super-8 films ) or 25 frames per second ( for television movies). Most silent films should be s presented with 16 to 22 frames / because they were shot at this speed, otherwise movements appear in fast motion. For scientific purposes projectors exist with variable within wide limits frame rates. Also communal movie theaters are mostly equipped with projectors with variable speed.

Due to the usual in German-speaking mains frequency of 50 Hz, the television uses 50 frames per second, that is, at a frame rate of 25 Hz in order to avoid interference films are therefore shown on TV instead of 24 Hz, 25 Hz, resulting in the running time is reduced by 4%. A film of 100 minutes (cinema ) Duration is on TV or on video so only 96 minutes.

A century were film projectors without competition. Since the year 2000, among other things, saving reasons " movies " increasingly digitally produced and disseminated, this is accompanied by a transition to digital film projection.

Components

The main elements of a film projector are

• The film drive (for example, a Maltese - cross - locking in conjunction with switching roller or a gripper), which advances the film in the dark phase, in order to project it in the light phase as long as possible resting can. The film is in a so-called film gate, where it is guided longitudinally, transversely and along the optical axis (see the nomenclature of the narrower film technology).
• The rotary shutter (sector plate ), which interrupts the light beam while the film is transported, and then once more at the center of the moment in which the film image is shown ( increasing the flicker frequency )

• The light source: with 35 mm film, as he is usually played in cinemas, this used to be carbon arc lamps, today there are xenon arc lamps usually between 900 W and 10 kW of electrical power (the largest standard Xenon lamps have 7000 W). For 16- mm films are partially xenon lamps, partially used halogen bulbs. 8 mm film projectors usually have halogen bulbs. First 35mm film projectors for home use also used for normal bulbs or even oil lamps.
• A condenser of the light source projected on the aperture plane of the objective,
• The image masks (picture window ) for the different image or projection formats, so soundtrack and perforation are also not visible on the canvas.

• The light valve, a metal screen between film and lamp which closes automatically in case of a blackout or projector stop and so the non- transported film before the heat lamp protects ( locks the door, melts the film); and otherwise served by the presenter to hide no demonstration imaginary parts of the film as the starting band. Other light flaps may seal the projection window ( by no more to project the Fim of not more active projector to the screen when blending ).
• The projection lens to the image equalized or sharp and projecting them into the right size on the screen
• Samples the sound device for optical sound or magnetic sound, the sound tracks of the movie

As current development replacing the mechanisms by a stepper motor in conjunction with switching role. Benefits are supposedly improved image stability, improved light utilization through shorter response times (the time needed to transport the film by one step ) and lower film and equipment wear. Furthermore, there are methods in which the film is not issued, but moved continuously. The light of the image passes through a system of rotating synchronously to the film movement prisms or mirrors in the lens. The company Ernst Leitz built the operating according to this principle Mechau projector. The method is also used in small imaging on a ground glass viewing boxes.

Movies in widescreen format be masked, that is, when projecting an excerpt of the maximum possible screen size is only shown. Accessible are the American widescreen with an aspect ratio of 1:1.85 and the European widescreen with an aspect ratio of 1:1.66. Must be distinguished from the CinemaScope process in which the film image is distorted during recording: so in width more information to be recorded, the image in the horizontal plane is compressed by a cylindrical lens. For the demonstration of such films, the projector must be equipped with an anamorphic lens, with which the image is equalized. The aspect ratio of the projected image is equalized with optical prints 1:2.35. To avoid blurred image edges are visible on the screen, limit there sliding matte black " iris " picture.

Film guide in the projector

The movie channel, ie the tortuous path that the film travels inside the projector is equipped with a plurality of rollers and sprockets. First you make by lateral webs that the film is exactly centered in the running direction. A first sprocket ( Vorwickelrolle ) pulls the film from the supply reel, which is in the upper fire drum. In coils and plate towers operating separate motors provide continuous film feed. It follows the first, upper film loop as a transition from the continuous movement for stopping - and - transport by the switching role.

Above this loop is the blackout switch that is raised when accumulates in a film tear film between Vorwickelrolle and movie channel. This drive motor and exciter lamp is then switched off, and also a light damper closes in front of the picture window. Since earlier flammable nitrate films were used, a fire switch was provided which was biased by a separate nitrate film loop. Began the passing copy fire, this loop also burned and replaced the fire switch. The same consequences entered as the blackout switch; additional case flaps were still raised in front of the projection and exhibition openings of the projection booth.

In the movie channel, which can be opened to insert (film door or slide ), the film between the film web having Sammetauflage and two Andruckkufen. Through the picture window of the mask a suitable image area is illuminated by the lamp and projected from clamped in the lens mount lens.

For cooling, inter alia, of the film in the movie channel a cooling water connection with inlet and outlet is partially available. Alternatively, or in addition to water cooling include some discussion of a valve disposed between the lamp and picture window heat-absorbing filter or an air cooling of the image window.

After the film has passed through the carriage, where he was projected frame by frame, followed by another film loop, then another sprocket ( Nachwickelrolle ), which put him back in continuous motion. To insert a movie, the projectionist stops the " principle of the longest path ".

After the bottom loop of the optical sound is arranged. The film first passes through a drag reel with rubber pressure and reaches the capstan, where the sound track is illuminated by the exciter lamp by slit optics and sensed by the photocell. The capstan is connected to a flywheel and will offset slinging movie in rotation from passing. The film then passes through a spherical roller, which ensures tight film location in the sound device, and is passed over the dentate Nachwickelrolle, wherein the lower roller prevents jumping out of the perforation in the lower fire drum. The driven lower coil axis wraps here the film on a reel ( fishing reel empty reel ) and a Bobby (a small coil core; formerly of wood, now made ​​of plastic).

All sprockets and the gripper system (switching role ) are synchronously coupled. Switching role, slide and image mask as a whole are vertically movable in order to adjust the picture at the film can. Through this image stroke adjustment allows the presenter - if the film is not loaded properly - ensure that the entire film image, but not the frame line lying between two images is shown. The runners pressure of the slide is adjustable to compensate the one hand mechanical differences of the film material (eg, waves, kinks, splices ) and the other to fix the image during his arrest safely. The rotary shutter must be adjusted so that it only releases the beam path during standstill of the film in their temporal position for switching role. More wings to increase their light-dark - frequency so that no flicker is perceived.

Before loading the film, the hand actuator is actuated until the switching role is just at rest. Now the film is inserted so that there is exactly one frame in the image window. Since the projector needs a certain time to ramp-up, usually not a film image, but an image of the starting strip is positioned in the image window. To make sure that it comes between the loaded image and the first actual image of the act no shift of the image position ( it is in fact usually black band with no visible frame line immediately before the first actual image ), the presenter should carry out an appropriate visual control. This can eg be done by letting the film by hand run over an old Vor-/Nachwickelrolle on which marks for the image line (see pic of the sprockets ).

There are 16 ways to insert a 35 - mm film. This number of combinations is obtained by multiplying

• 2 options for the running direction ( beginning or end → end → the beginning)
• Two possibilities for the location of the audio track (or the lateral position of the image)
• 4 ways for inserting a single image in the image window (corresponding to 4 perforations per frame ).

Of these 16 possibilities only leads one immediately to correct a projection in three other is, after all, a correction by the image line adjustment possible. In the remaining 12 cases, the performance should be interrupted and the film to be re- inserted. Correctly, the film is loaded when

• The film beginning in the direction of the projector is running ( " heads down " )
• The audio channel in the viewing direction is to the right canvas
• Precisely, an image is inserted into the image window

To protect the film all the roles ( and other parts that come in contact with it or can get, such as the movies, but also the blackout switch) are designed so that only the perforation with these parts come into direct contact. Therefore, in the region of the actual image corresponding recesses provided (see, for example, imaging of the sprockets ).

In the resting state should always be open to the movie channel and all pinch rollers. No one notices this, can form flat spots that cause disturbances in particular in the rubber pressure of the sound unit.

Film guide to the projector

The guide of the film within a projector is always the same. There are differences in the manner in which and re-entering the film for projector.

Fade operation

Films are traditionally delivered in " files ". This designation has taken over from the theater. An act is to 2000 Filmfuß long ( 600 meters ), which is equivalent to 22 minutes of run time. Earlier, the film rolls were packed in tin cans or flat cardboard boxes, mostly today in plastic round containers. The distribution of movies to multiple file was previously necessary because the focal length of the coals of a charcoal - arc lamps was limited to about 45 minutes. A normally long (game) film of 90 minutes would therefore can not be shown without interruption. In addition, as the transport has been simplified ( would a 90 -minute film wound on a single coil, this would have a diameter of about one meter).

The file will be delivered wound on spools not, but on the Bobbies already mentioned.

Usually every act at the beginning and end has a colored protective film, allonge, which allows the presenter to recognize immediately the type of act it is and whether it is wrapped "in the beginning " or "at the end " - depending on whether Aktanfang or Aktende are on the outside. However, it is advisable not to rely as a projectionist at the Allongen, but make a visual inspection.

After the allonge follows the start band called, also called " Blank Film" ( because the film contains no frames ). After the film, the images and the audio to begin contains. The sound track is offset by a few images "before" the actual projected image as sampling, amplification, require management to the speaker and sound propagation to the ear of the spectator a certain time and would otherwise asynchrony between lip movements and words were.

Are two projectors available ( called "a couple " ) then they are mirror images (fachsprachlich a left and a right machine, depending on whether the film is seen in projection towards the left or right side of the machine ) so that the projectionist both machines can use the same intermediate course.

For demonstration purposes, the Act must be wound "in the beginning ", the film leader must be on the outside of the roll. At the end of the projection are the beginning inside the film roll. The roll must therefore be rewound before the next presentation so that the top is the outside again.

When the film is removed after the last performance directly from the winding and (using a detachable take-up reel ) placed directly into the transport box, then back to the beginning inside. A projectionist must therefore ensure that, before the presentation, whether in the roles of the beginning is on the outside.

For very often played copies the perforation suffers and can fray and tear. Does the film so not around the Umlenkspulen in the projection apparatus, a film tear can occur there, which naturally leads to chaos in the screening room. Most of the film is still reeled off a few feet and fills the space before the blackout switch stops the film transport. Then the film is convoluted, to save time, cut and re- inserted the film in the projection apparatus. The newly loaded film is provisionally wound on the take-up roll until the friction there, " entrains " him and rewinds. The unwound in space piece of film must later be installed when rewinding the film. To avoid such cracks film, the perforation must be checked (see film assembly) in old copies.

The Art of the presenter is also to start at the end of an act of the projector with the following act in time and switch the picture and sound, so that viewers do not notice a transition. Coming to his aid also " fade (ing ) sign " are towards the end of an act called Aktwechselmarken called, copied in the upper right corner of the image or scratched. With the appearance of the first marker of the presenter starts the second projector ( light and drive), at the second mark will fade ( coincides with the launch of the second projector for the first projector light valve between the lens and the projection window and prevents the images mingle or first projector " idle ", the projected image of the second projector unnecessary brightens. both characters are necessary because the projector some time to ramp-up required (For details on timing, see there). Weil suffer from frequent demonstrations the Act, it is advisable own fade characters eg platinum tape ( which can be removed without leaving any residue ) to install. Experienced presenters can sometimes detect the diameter of the unwinding when the second projector is about to start.

There are projectors that decrease the presenter manual crossfading. For this purpose, small pieces of a metallic self-adhesive tape to be applied to the film. A scanner responds to this and takes steps otherwise to be carried out manually, ie the start of the second projector and the transition. With three or even four projectors can be run automatically in this way up to an hour program. Today, in general, all acts of the film are coupled prior to performance (ie, stuck to each other ) and with one of the procedures described below demonstrated.

Coil operating

The individual acts of the film copy (without allonge, Black film and start tape ) consecutively bonded ( "coupled" ) and wound on a spool. The beginning of the film is on the outside. The "upper" or film -forming reel is unwinding, the reel on which the film is wound up after the projection, is take- up spool or fishing reel. When the film is to be shown by a projection again, it must first be rewound from the take-up reel to the supply reel. Pairing is on an inspection table, a structure with two small, aktgroßen plates (often still operated by hand crank ) and a splicer next to it.

There are projectors, whose unwinding and Aufwickelfriktionen lie vertically above each other, with both coils on the lamp house next to each other are attached. Finally, there are coil towers that are directly next to the projector or at a distance. Since the mass of such a coil with a complete film is too large to be moved from the first sprocket of the projector without damage to the perforation can has its own motor, which adjusts its speed according to the degree of processing.

Control operation

For the non-stop screening of movies with a projector, there are next to the coil tower since the late 1960s, the so-called plate systems in which the film is lying horizontally on a large plate levels. For demonstration purposes, the beginning of the film is taken out from the center of the reel and wound up on a different level. A further development for special cases represents the continuous plate

Control and automation in the screening room

See separate article matrix machine.