GB2071863A

GB2071863A - Projector or viewer for cine film having the facility of single- frame operation

Info

Publication number: GB2071863A
Application number: GB8105393A
Authority: GB
Original assignee: Agfa Gevaert AG
Current assignee: Agfa Gevaert AG
Priority date: 1980-03-14
Filing date: 1981-02-20
Publication date: 1981-09-23
Also published as: DE3009791A1; DE3009791C2; ATA102581A; IT8148025A0; AT371940B

Abstract

A film guide track 3, 5 guides a cine film 7 between a lamp 1 and a projection lens 2, and is composed of a relatively flexible guide 5 nearer the lens and a relatively rigid guide 3 nearer the lamp. A projection window 4 in the guide track permits light to pass from the lamp 1 to the lens 2, and includes a planar glass plate 8 on the guide 3. During normal cine operation, the heat from the lamp 1 causes the film to bow convexly thereto and into contact with the plate 8. When the projector or viewer is used to project or view a single frame of the film, excessive bending of the film which would otherwise throw the projected or viewed image out of focus is prevented by the glass plate 8. This can be assisted by streams of cooling air from a ventilator 6 directed respectively onto the lamp-facing surface of the glass plate 8 and between the guide 5 and the projection lens 2. <IMAGE>

Description

SPECIFICATION Projector or viewer for cine film having the facility of single-frame operation This invention relates to a projector or viewer for cine film having a facility for projecting or viewing a single frame of the film.

In conventional projectors and viewers of this type, the film is cooled where it passes between a lamp and a projection lens to a degree which is just enough to prevent excessive overheating when the projector or viewer is used in cine mode (i.e. the film is transported continuously therethrough). This means that the film is exposed to a considerable amount of heat when the projector or viewer is used for the projection or viewing of a single frame. Since a guide track, which guides the film between the lamp and the projection lens, is normally directed towards the lamp, the film will arch or dome out transversely to the direction of its transportation so that it is convex to the lamp (and hence also concave to the projection lens).

During single-frame projection or viewing, this convex deformation towards the lamp is greatly increased so that the projected or viewed image soon goes out of focus and becomes blurred. Consequently, when operating the projector or viewer alternately in cine mode and single-frame mode, the operator must continually re-adjust the focus of the projection lens.

It is an object of the present invention to obviate or mitigate this problem by restricting the spherical deformation of the film during the projection or viewing of a single frame so that the image can be maintained in approximate sharp focus without adjustment of the projection lens.

Accordingly, the present invention provides in one aspect thereof a cine projector or viewer having a single-frame projection or viewing facility and comprising a lamp, a projection lens, and a film guide track which leads a film between the lamp and the projection lens, the film guide track including a projection window through which light passes from the lamp to the projection lens and which is formed by a light-transmitting plate.

According to a second aspect of the invention, a projector or viewer for cine film comprises a lamp, a projection lens, a film guide track for guiding said film through a space between the lamp and the projection lens, the film guide track including a projection window through which light passes from the lamp to the projection lens and which is formed by a light-transmitting plate, and transport means operable selectively to transport said film continuously along the film guide track and to arrest said film for projection or viewing of a single frame of said film.

Advantageously, the film guide track includes a pair of guides disposed in face-toface relation and spaced apart transversely of the direction of film transport, said film passing between the guides in use, the guide nearer the projection lens being flexible as compared with the guide nearer the lamp. In this case, the light-transmitting plate is preferably arranged so that it is flush with the guide nearer the lamp, although it may alternatively be slightly set back in relation thereto.

The projector or viewer can also comprise a ventilator providing two stream of cooling air, one of which sweeps a side of the lighttransmitting plate facing the lamp, the other passing over a surface of the film which faces the projection lens and preferably between the projection lens and the guide nearer thereto.

The ventilator can also provide one or more further streams of cooling air directed into the reflection range of the lamp.

The light-transmitting plate is preferably made of glass.

The present invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an exploded perspective view of the essential parts of a projector or viewer for cine film, according to the present invention; Figure 2 is a sectional side view of a modified form of projector or viewer, also according to the present invention; and Figure 3 is a similar view to Fig. 2 but showing the film during projection or viewing of a single frame thereof.

Referring to the drawings, the apparatus shown therein (which is applicable to both a projector and a viewer) comprises a lamp 1, a projection lens 2 and a film guide track 3 which guides a cine film 7 through a space between the lamp and the projection lens. The film guide track includes a pair of guides 3, 5 disposed in face-to-face relation and spaced apart transversely of the direction of film transport, the film 7 passing between the guides 3 and 5. The guide 3 nearer the lamp 1 is relatively rigid, whereas the guide 5 nearer the projection lens 2 is comparatively flexible. A projection window 4 is provided in the film guide track to allow light from the lamp 1 to pass to the projection lens 2, and includes a glass plate 8 on the guide 3.

Although not shown, a transport mechanism is provided for the film and is operable selectively to transport the film continuously through the guide track (cine mode) and to arrest the film for projection or viewing of a single frame (single-frame mode). As shown in Fig. 1, the film is transported horizontally through the guide track 3, 5: however, the whole arrangement could be turned through 90 so that the film is transported in a vertical direction.

The glass plate 8, which is planar at least on that side thereof which faces the film is of a size at least equal to the size of a single frame of the film 7. The glass plate 8 may be thin, with planar parallel surfaces, or may be a finely ground glass plate in which event, whilst absorbing some of the light from the iamp, it would provide a more uniform light distribution. In the embodiment of Fig. 1, the glass plate 8 is set in the guide 3 so as to be flush with the latter. In the embodiment of Figs. 2 and 3, however, the glass plate 8 is slightly set back relative to the film track towards the lamp 1 Whichever arrangement is preferred in a given case will depend on the type of the guide 5 nearer the projection lens 2 and the force which it applies to the film.If the elastic application force of the guide 5 is very strong so that the film edges are subjected to considerable degree of compression in the projection window. the slightly recessed position of the glass plate 8 shown in Figs. 2 and 3 will be of advantage. if, on the other hand, the guide 5 is softly elastic and resilient, then a flush mounting of the glass plate 8 in the guide 3 as shown in Fig. 1 would be preferred. In any case, the glass plate 8 must be so arranged that the apex 7a of a film frame which has deformed convexly relative to lamp 1 ( as shown in Fig. 2) makes some physical contact with the film-facing side of the glass plate 8 at normal heat exposure during operation in the cine mode.The objective lenses of projectors are normally corrected for this normal heat deformation so that the projected or viewed image will be in sharp focus over its entire area.

If the projector or viewer is operated in single-frame mode so that one frame of the film is projected or viewed for a longer period of time than in cine mode, this part of the film will be subjected to a considerably greater amount of heat from the lamp 1. If the projection window on the lamp side were simply an open space, the film region corresponding to the projected frame thus heated would bulge strongly into this open space so that it would be progressively less and less sharply focussed by the lens 2, especially in the middle of the picture which is usually the most important region.In the present apparatus, however, due to the presence of the glass plate 8 in the projection window, the film on heating up in the course of still projection progressively approaches and marries with the planar surface of the plate 8 starting from the apex 7a, i.e. from the centre of the picture, and is thus kept approximately in the focussing plane of the lens 2. The projected or viewed image therefore remains sharply focussed without the need to adjust the lens 2, even during single-frame projection or viewing. The position of an individual film frame during prolonged still projection is shown, albeit slightly exaggerated, in Fig. 3.

If required, namely depending on the degree of heat distortion for which the projection lens 2 is corrected, the above-described favourable effect of the glass plate 8 may be further assisted and improved by the provision of cooling air streams produced by a ventilator 6 ( Fig. 1) arranged either laterally of or beneath the film guide track 3, 5. In a preferred arrangement, a cooling air channel 9 extends from the ventilator 6 on the lamp side to directly above the guide 3, so that a flow of cooling air cools the glass plate 8 on the lamp side thereby reducing the amount of heat applied to the film 7 in the projection window, particularly during single-frame operation. In this way it is possible to prevent the film from clinging almost flat to the glass plate 8 in single-frame operation and to preserve more of the concave deformation relative to the lens 2. This effect may be further assisted by the provision of a further cooling air channel 10 from the ventilator 6 which blows cooling air in front of the projection window 4 on the lens side.

Since the lens is focussed on the lens-facing side of the film, any dust particles which may be present on the glass plate 8 or between the film 7 and the glass plate 8 are outside the focal plane and therefore remain unobserved in the projected or viewed image. The glass plate 8 affords the additional bonus that is contributes to a more uniform friction of the film 7 relative to the film guide track during operation in the cine mode because varying film distortions can no longer bay out into an open aperture on the lamp side.

Claims

1. A cine projector or viewer having a single-frame projection or viewing facility and comprising a lamp, a projection lens, and a film guide track which ieads a film between the lamp and the projection lens, the film guide track including a projection window through which light passes from the lamp to the projection lens and which is formed by a light-transmitting plate.

2. A projector or viewer for a cine film comprising a lamp, a projection lens, a film guide track for guiding said film through a space between the lamp and the projections lens, the film guide track including a projection window through which light passes from the lamp to the projection lens and which is formed by a light-transmitting plate, and transport means operable selectively to transport said film continuously along the film guide track and to arrest said film for projection or viewing of a single frame of said film.

3. A projector or viewer as claimed in Claim 1 or 2, wherein the film guide track includes a pair of guides disposed in face-toface relation and spaced apart transversely of the direction of film transport, said film passing between the guides in use, the guide nearer the projection lens being flexible as compared with the guide nearer the lamp.

4. A projector or viewer as claimed in Claim 3, wherein the light-transmitting plate is flush with said guide nearer the lamp.

5. A projector or viewer as claimed in any preceding Claim, further comprising a ventilator providing two streams of cooling air, one of which sweeps a side of the light-transmitting plate facing the lamp, the other passing over a surface of said film which faces the projection lens.

6. A projector or viewer as claimed in Claim 5 when appended to Claim 3 or 4, wherein said other stream of cooling air passes between the projection lens and the guide nearer thereto.

7. A projector or viewer as claimed in Claim 5 or 6, wherein the ventilator also provides one or more further streams of cooling air directed into the reflection range of the lamp.

8. A projector or viewer as claimed in any preceding Claim, wherein the light-transmitting plate is made of glass.

9. A projector or viewer substantially as hereinbefore described with reference to the accompacying drawings.