Film projection system

A film projection system for use with a continuous film motion telecine machine includes a film guide (17, 18) which guides the film (1) past a gate (13). The film guides (17, 18) form part of two endless bands (14, 15). The parts of the bands (14, 15) in contact with the film (1) are arranged to move at substantially the same velocity as the film and there is provided means (19, 20) for varying the spacing between the bands.

The invention relates to a film projection system including a light source, 
film transport means for continuously transporting the film past an 
aperture through which light from the source is directed and a guide for 
guiding the film in the region of the aperture to maintain a desired 
spacing between the film and the aperture, the guide being arranged to 
move at substantially the same velocity as the film. 
The invention further relates to a telecine machine including a film 
projection system as described in the preceding paragraph. 
A film projection system as described in the opening paragraph is disclosed 
in U.K. Patent Specification No. 1349857 which shows a film transport 
means comprising a drive roller and a flexible belt which passes round the 
drive roller and a following roller and forms a guide for the film which 
moves at the same velocity as the film. The flexible belt is optically 
transparent. The flexible belt has a film receiving channel in its outer 
surface, the width of the channel being such that the sides thereof engage 
the edges of a film received in the channel. 
This film projection system suffers from the disadvantage that if different 
sized films are to be projected e.g. 8, 16 or 35 mm it is necessary to 
remove the flexible belt and replace it with a different belt having a 
different width channel. 
The invention provides a film projection system as described in the opening 
paragraph characterised in that the guide comprises two endless bands each 
having a portion which engages with respective edges of the film and that 
there is provided means for varying the spacing between the bands. 
The provision of means for varying the spacing between the bands enables 
the projection system to be used for different sized films without 
requiring the substitution of parts of the film drive or guide mechanisms. 
The bands may be located on and encircle a single turret which may be in 
the form of a hollow cylinder having an aperture in its curved surface. 
The means for varying the spacing between the bands may comprise a carrier 
for each of the bands, the carriers being slidably mounted on the turret 
and being locatable by means of spring loaded balls engaging in indents. 
The turret may be mounted on an opaque deck, the light source being located 
on the opposite side of the deck from the turret and light from the source 
being reflected through the aperture. 
Sound reading transducers may be located adjacent to the guide means 
enabling a compact construction to be achieved. 
To enable the sound transducers for both 16 mm and 35 mm films to be both 
located adjacent the guide means spaced rollers may be provided to enable 
a loop to be formed in the film between the apertures and the sound 
reading transducers. The use of the spaced rollers enables the different 
spacing between the film and sound track for the two types of film to be 
compensated for.

FIG. 1 shows a diagrammatically telecine apparatus in which a film 1 from a 
reel 2 passes through a tension arm assembly 3 which comprises two rollers 
4 and 5 which are biased to produce a given tension in the film. The film 
then passes round a further roller 6, a turret 7, roller 8, and tension 
arm assembly 9 comprising two rollers 10 and 11 to a take up reel 12. 
The turret 7 is in the form of a hollow cylinder and as can be seen from 
FIG. 3 has a gate aperture 13 in its curved surface. Two endless bands 14, 
15 (FIG. 3) are located on and encircle the turret 7 and are friction 
driven by a drive roller 16. Each of the bands has a portion which engages 
the respective edge of the film. The portions of the bands 14 and 15 
locate the film 1 and transport the film round the turret 7 and past the 
gate 13. Thus the annular bands 14 and 15 act both as film transport means 
for continuously transporting the film in conjunction with the drive 
roller 16 and as a film guide in the region of the gate 13 in order to 
maintain a desired spacing between the film and the gate 13. A plane 
mirror 47 located within the turret 7 reflects light from a source (not 
shown), which is located under a deck 48 on which the turret is mounted, 
through the gate 13. The bands 14 and 15 are coated with a soft high 
friction material such as rubber at least over the surfaces 17 and 18 in 
contact with the film 1 so that there is little or no slip between the 
film 1 and the bands 14 and 15. 
The bands 14 and 15 are mounted on carriers, formed by rings 19 and 20 
respectively, ball races 21 and 22 providing a low friction bearing 
surface between the bands 14 and 15 and the rings 19 and 20. The rings 19, 
20 are slidable on splines 29, 30 between two positions to accommodate 
both 16 mm and 35 mm films. In this way there is provided by the rings 19 
and 20 means for varying the spacing between the bands 14 and 15. The ring 
19 is located by indents 23, 24 and the ring 20 by indents 25, 26. When 
the rings 19 and 20 are located by the indents 24 and 25 the bands 14 and 
15 are spaced for 16 mm film while when the rings 19 and 20 are located by 
the indents 23 and 26 the bands 14 and 15 are spaced for 35 mm film. 
Further indents may be provided on the turret 7 to enable the bands 14 and 
15 to be spaced for any other film size. 
The ring 19 is located in the indent 23 or 24 by means of a spring loaded 
ball assembly comprising a coil spring 27 and a ball 28. There are 
typically three identical assemblies located at 120.degree. intervals 
round the circumference of the ring and three corresponding indents on the 
turret 7. The spring and ball assemblies could alternatively be located in 
the turret 7 with co-operating indents being formed in the rings 19 and 
20. 
A light source (not shown) such as an incandescent lamp is located under 
the deck 48 and is reflected by the mirror 47 through the gate aperture 13 
onto the film 1. The chain dotted line 49 in FIG. 3 shows the path of 
light from the source through the gate to the detector. 
As shown in FIG. 2 three further rollers 30, 31 and 32 may be provided to 
enable a loop of film to be formed. This enables sound transducers 33, 34 
and 35 to be located adjacent to the turret 7. The transducer 33 is 
positioned to read an optical sound track on 35 mm film and in order that 
the correct synchronisation between the film and the sound track is 
obtained the film is taken in a loop round the rollers 30, 31 and 32. For 
16 mm film the spacing between corresponding film frames and soundtrack is 
closer enabling the film to be taken directly round the turret to obtain 
the correct spacing between the transducer and the film gate. 
The lower part of FIG. 1 shows an optical scanning system which enables a 
continuously moving film frame to be focused on a detector. In principle, 
the scanning system comprises a scanning mirror 123, which is pivotable 
about an axis 132 perpendicular to the plane of drawing, and at least one 
row of radiation sensitive detectors 129, which row extends 
perpendicularly to the plane of drawing. Furthermore, there is provided an 
imaging system comprising the semitransparent mirrors 120 and 124 and the 
concave mirrors 121 and 125. 
The scanning beam 140 which passes through the film 1 is partly reflected 
to the concave mirror 121 by the semitransparent mirror 120. The mirror 
121 reflects the incident light to the semitransparent mirror 120, which 
transmits a part of the beam to the scanning mirror 123. Upon reflection 
by the scanning mirror a part of the beam passes through the 
semitransparent mirror 124 and is subsequently incident on the concave 
mirror 125, which again reflects the beam. Via a further reflection on the 
semitransparent mirror 124 the scanning beam is directed to the row of 
detectors 129. 
The concave mirrors 121 and 125 are rectangular concave mirrors, whose long 
axes are perpendicular to the plane of drawing. The system 120, 121, 123, 
124 and 125 conjugates each point in the plane of the film gate to a 
separate point in the plane of detectors. Conversely, it may be said that 
the row of detectors is imaged on the film as a narrow strip whose 
longitudinal direction is transverse to the plane of drawing. Thus, at any 
instant a row of detectors observes only a narrow strip of a film frame 
being scanned. The width of this strip, hereinafter referred to as 
scanning line, is determined by the magnification of the system of concave 
mirrors 121 and 125 and by the height h of the detectors. 
FIG. 4 shows a detector row 29 in front view. This row comprises a number 
of separate detectors d.sub.1 to d.sub.n, for example photodiodes, 
phototransistors or other photosensitive elements. The height, i.e. the 
dimension transverse to the plane of drawing in FIG. 1, and the 
magnification of the selected optical imaging system dictate the length l 
of the detector row. The technology used in the manufacture of the 
semiconductor detectors determines how many detectors, having a length l', 
can be realised within the length l. This also defines the number of 
points of a scanning line that can be resolved. The imaging optics should 
be such that the detectors d.sub.1 to d.sub.n are separately imaged on the 
film. 
Which line of a film frame located within the film gate is scanned at a 
specific instant is obviously determined by the position of the scanning 
mirror at this instant. FIG. 1 shows the situation in which the scanning 
line is in the centre of the film gate. When the mirror 123 is rotated 
anti-clockwise or clockwise the scanning line is moved to the left and the 
right respectively. 
The focus of the concave mirror 121 is situated at the front of the film 1, 
i.e. the side where the picture information is located. Between the 
mirrors 121 and 125, and thus also at the location of the scanning mirror 
123, the beam 140 is a parallel beam. This ensures that, independently of 
the position of the scanning mirror, the beam 140 is always sharply imaged 
on the detector row and that no magnification errors can arise. 
The first part of the imaging optics by means of which an area of the sizes 
of two film frames is to be imaged, will always include a concave mirror 
121. By means of the part of the imaging optics behind the scanning mirror 
only one line need be imaged. Therefore, the concave mirror 125 may be 
smaller than the concave mirror 121. The semitransparent mirror 124 and 
the concave mirror 125 may also be replaced by a preferably achromatic 
lens system, such as a doublet. Such a lens system can be cheaper than a 
mirror system. Moreover, less light is reflected in that case, so that 
more light is available for the detectors. 
In principle, the scanning mirror 123 is a plane mirror. However, the 
reflecting surface of this mirror may also be slightly curved and thus 
function as a kind of spherical Schmidt corrector, by means of which the 
imaging errors of the optical mirror system can be corrected. If the 
elements 124 and 125 have been replaced by a lens system, steps can be 
taken to ensure that this lens system corrects the imaging errors of the 
mirror optics and the scanning mirror itself may be entirely plane. 
Generally, the film to be scanned will be a colour film. In that case, as 
is shown in FIG. 1, a colour splitting system 126 will be included between 
the semitransparent mirror 124 and the detection system, and the detection 
system will comprise three rows 129, 130 and 131 of radiation sensitive 
detectors. The detector rows 130 and 131 are constructed in a similar way 
as is shown in FIG. 4 for the row 129. The system 126 may be constituted 
by a colour splitting prism containing two dichroic layers 127 and 128. 
The layer 127 for example only reflects the blue colour component of the 
incident light to the detector row 130 and transmits the rest of the 
light. The layer 128 for example reflects only the red colour component of 
the incident light to the detector row 131. After traversing the layers 
127 and 128 only the green light component of the incident light is left. 
This component is incident on the detector row 129. 
Colour separation may also be achieved with the aid of a diffraction 
grating in the form of a phase grating, which comprises a multitude of 
each time three grating grooves, which three grating grooves have 
different depths. Such a colour separation grating is for example 
described in the German Patent Application No. 2,645.075, which has been 
laid open for public inspection, and is not discussed in more detail. When 
a colour separation grating is used the three rows of detectors may be 
arranged adjacent each other in one plane, the rows having the same 
direction as the grating grooves. If the detectors comprise photo diodes, 
the three rows of detectors may be integrated on one substrate, so that 
the detection system of FIG. 1 may be replaced by a very compact system. 
The optical scanning system shown in FIG. 1 is more fully described and is 
claimed in U.K. Patent Application No. 2044578A. Alternative scanning 
systems could be used to freeze the continuous motion so that individual 
frames of the film may be sequentially presented to a detection device. 
The detection device may alternatively be a television camera tube in 
which case it is necessary to produce a stationary image of each film 
frame on the active surface of the camera tube. The film projection system 
in accordance with the invention is not limited to use with the scanning 
and detection arrangement shown in FIG. 1 but may be used with any 
suitable scanning system such as scanning mirror, flying spot scanning or 
sequential to interlace conversion using a digital memory. 
It is possible to interchange the positions of the light source and the 
scanning arrangement so that the light source is above the deck and the 
mirror 7 deflects the film image downwards to the detection system. 
Various alternative embodiments could be constructed in accordance with the 
invention. For example, the bands 21 and 22 could be made from flexible 
materials and be located on driving and following shafts the bands being 
carried by pulleys which are located on the shafts by a similar means to 
that by which the rings 19 and 20 are located on the turrets. It may, in 
this case, be necessary to provide additional guide means for the bands 14 
and 15 in the region of the film gate by, for example, providing guide 
pulleys on further shafts located adjacent to the film gate.