Film Projection Systems: A Comprehensive Guide to Traditional and Digital Techniques

Posted on Aug 20, 2024 in Technology

1.2 Components of Projection Systems

The projection system is the heart of any cinema, responsible for displaying the film on the screen. It consists of several key components, each playing a crucial role in the projection process:

  • Cruz de Malta (Maltese Cross): This drive mechanism keeps the film in constant oscillation between movement and rest. It consists of two parts: the cross and the impeller plate. The arms of the cross move the film and position it for exposure to light.
  • Shutter: The shutter interrupts the projection during the process of changing the image, preventing flickering.
  • Window: The window is smaller than the frame of the movie (21×17.5 mm compared to the 21.5×18 mm frame). This prevents separation lines and sound sidebands.
  • Optical Aperture: This rectangular opening allows the edges of the frame to be projected depending on the film format.
  • Optic Group: This group consists of one to three lenses in a turret. Like camera lenses, they are classified as normal, wide-angle, or telephoto lenses and are used depending on the distance between the projector and the screen.
  • Flashlight or Projection Lamp: This component provides the beam of light for the projector. The type of lamp chosen depends on the required light intensity, screen size, and distance between the projector and the screen.
  • Sound Reader: There are two types of sound readers, depending on the film’s soundtrack:
    • A-Optical: Located behind the exit of the film loop, after the Maltese Cross, to compensate for the gap with the image. It consists of a metal housing, a filter roll that removes oscillations, a lamp, a micro-lens, and a photodetector.
    • B-Magnetic: Less common, used for exclusive formats between 70 mm and 16 mm and unusual for 35 mm. It is situated between the supply roller and the window. It consists of two pairs of rollers and a head phone loop sensor that collects magnetic signals.

The quality of sound in film projection depends on several factors:

  • The screen, responsible for the intensity of reflected light.
  • The projection objectives, responsible for light distribution on the screen.
  • The shutter mechanism and projector drag, responsible for twinkling and blinking.
  • The intermittent drive mechanism, responsible for the oscillation of the image.
  • The focus of light emitted from the projection lantern, responsible for the quantity and quality of light.

1.3 Traditional and Digital Projection Rooms

A-Traditional Room: The current system of film projection in theaters is based on the physical presence of the plastic copy of the film in the projection booth. The film must be collected from a warehouse, transported to the local cinema, and the corresponding coils mounted on the projector. This projector is equipped with a powerful light source that emits white light onto a screen. The film passes through a window, holding each frame for a fraction of 1/24 seconds ahead of the light source, projecting the photographic image onto the screen with its range of colors. This system requires a person to collect, transport, and return the physical copy of the film. The projection room must be acoustically isolated to prevent the noise of the projector from reaching the audience. It also requires two people to make the joints of the coils, mount the film, and control the projection.

B-Digital Room: Digital cinemas are equipped with automatic digital projectors that form images on the screen through the combination of three colors: red, green, and blue, to integrate the full range of possible colors. These three light sources within the projector respond in milliseconds to digital signals that determine the projection. The film comes through cable, fiber optics, radio waves, or satellite. Digital signals received contain all necessary information, including chrominance (color points to be illuminated) and luminance (intensity with which each point should light up). It also contains sync, vertical, and horizontal information, making it possible to form the image on the screen. A digital cinema operates automatically without physical projection of a copy, requiring no separate cabin and no projectionist to handle the copy and the projector.

1.4 Advantages of Digital Projection

Digital projection offers several advantages over traditional film projection:

  • Image Quality: Digital projection ensures high resolution (4 million pixels per frame), brightness (10,000 lumens), a billion colors, and consistent sharpness over time.
  • Sound Quality: Digital cinema provides superior sound quality by sending the encoded signal directly to the cinema, faithfully reproducing the different effects of the film through 8 satellite channels.
  • Live Releases: Digital projection allows for simultaneous releases with Hollywood premieres, even with the input and opinions of the artists.
  • Live Events: Digital cinema enables viewers to experience live events, such as concerts, sporting events, and bullfights, as if they were in the front row.
  • Ease of Management: Digital projection is automated, with programming provided by satellite.
  • Savings in the Cost of Copies: Digital projection eliminates the need for physical film copies.
  • Savings in Distribution Costs: Digital cinema delivers the signal directly to each cinema.
  • Instant Control: Digital projection allows for instant control of the number of spectators and the quality of the projection in each room.

1.6 Structure of Cinemas

A cinema is a venue for film screenings open to the public upon payment of an entry price. The necessary elements for a film session include:

  • Seats or Chairs: Cinemas offer a variety of seating options, with a focus on comfort and convenience.
  • Projection Booth: This booth houses all the mechanisms, tools, and instruments involved in the projection process. It must have an air conditioning system to remove heat from the lanterns and spotlights.
  • Screen: The screen is the surface onto which the film is projected.
  • Speakers: Speakers are strategically arranged around the room to create a realistic sound experience. A combination of speakers specializing in different frequencies (low, mid, and treble) is used. The location and layout of the speakers are crucial for creating a surround sound effect, where the inner soundtrack corresponds to the speakers near the screen, while the sidebands correspond to speakers further away.

1.7 New Projection Techniques

New projection techniques began to develop in the 1960s as a result of experimentation with new formats, mainly the 70 mm format, increased projection speed (between 48 and 60 frames per second), and the use of spherical screens. Some of these techniques include:

  • Cinerama: Recording is done with three cameras, and projection is done with three projectors onto a concave screen with a depth of 7 meters in its central arch. This curvature limits the optimal viewing point to the center position. A fourth projector is responsible for reproducing the soundtrack.
  • Cinemascope: The image is compressed within the 35 mm negative during recording using anamorphic lenses. The same type of lens is used on the projector to decompress the image during playback. The display requires a curvature of 1.5 meters deep at its central arch and can be viewed from anywhere in the room, maintaining the rectangular format. Cinemascope laid the foundations for the technical and artistic possibilities of large formats: speed, panoramic views, lighting, color, and epic staging.
  • Vista-Vision: To increase the surface impressed by the 35 mm frame during recording, the film is transported horizontally. This increases the number of perforations per frame to eight. It is the antecedent to the Imax system.
  • Imax: Developed in Canada by Imax Corporation, Imax is an integrated system from recording to playback. The first exhibition was held at the Imax Montreal Expo 1967 with the movie Labyrinth, recorded with 5 cameras in 65 mm format, with 15 perforations per frame. For playback, 5 screens were assembled vertically and horizontally. There are currently two types of Imax: HD, which uses 70 mm format screens, and Imax 3D, which uses 70 mm film with 15 holes and horizontal step, reproduced at 48 frames per second on a giant screen.
  • Omnimax: Also developed by Imax Corporation, Omnimax was originally used for projection in planetariums. Recording is done with a fisheye lens, and projection is made onto a hemispherical screen placed at an angle to the audience, who are situated in reclining seats. It occupies the entire field of human vision and immerses the audience in the picture. It uses a 70 mm format with fifteen horizontal perforations, reproduced at 48 frames per second.
  • Solid: (Imax Corporation) is a 3D simulation system. Projection is made on a spherical screen with two projectors whose lenses are synchronized to alternately reproduce the image on the right and left 96 times per second. The three-dimensional impression is achieved through a 3D generator that breaks the Photosynthesis in vision, but it is imperceptible to the eye.
  • Magnavision: Uses 70 mm format with five holes and is played on a 180ยบ screen.
  • Showscan: Uses 70 mm format with five holes, played at 60 frames per second.