ABSTRACT
Telecines may also be described as motion picture film scanners. The term telecine refers to a film scanner designed to provide television signals from the film image. The term film scanner is presently used to describe devices that can also provide images in a digital data form more closely related to computer image files than television signals. Telecines can be grouped into three distinct types: photo-
conductive, flying spot and CCD. The term photoconductive applies to those telecines that
incorporate an electronic tube camera as the pick-up device; a variety of camera tubes can be used, such as plumbicon, vidicon, saticon, etc. The light source is usually a tungsten halogen lamp and the projector will have an intermittent film transport so that the image on the film frame can be transferred to the camera tube target while the film is stationary, a necessary requirement since the camera tubes exhibit storage characteristics. The colour photoconductive camera has three separate tubes to produce the red, green and blue signals, and the scans on these tubes have to be accurately matched to obtain colour registration. Photoconductive telecines have not been manufactured since the 1970s and are therefore of historic interest only. Flying spot telecines can be grouped into two distinct types:
Cathode Ray Tube (CRT) and Laser-based telecines. The CRT-based flying spot telecine uses a single, white light,
flying spot cathode ray tube with an unmodulated raster as a light source. An image of the raster is projected onto the film by an object lens. Light passing through the film is modulated by the film image, and the light is then collected and directed through colour splitting optics to photomultipliers or in more recent telecines to Large Area Avalanche PhotoDiodes
(LAAPDs) which produce the electrical signal. Such detectors are generally referred to as photoelectric cells (PECs). Since the colour splitting process occurs after the imaging
process, there is no requirement for colour registration when using a white light CRT-based scan (see Figure 4.8.1). Laser telecines have been built experimentally; such devices
rely on three unmodulated RGB lasers whose flying spot beams are combined to project onto the film image. As with the CRTbased telecine, light passing through the film is modulated by the film image and is directed through colour splitting optics to PECs which produce the electrical signal. At the time of writing the author knows of no laser-based telecines that are commercially available. CRT-based flying spot telecines at present being manufac-
tured use continuous motion film transports, although there may be a small number still in use which have a 16mm transport with intermittent motion and a film frame pull-down time of 1.2ms.
