GB2253279A

GB2253279A - A light modulator

Info

Publication number: GB2253279A
Application number: GB9104160A
Authority: GB
Inventors: Alexander Charles Paton; Merlin Benedict Christo Milner
Original assignee: LIGHT WORKS Ltd
Current assignee: LIGHT WORKS Ltd
Priority date: 1991-02-27
Filing date: 1991-02-27
Publication date: 1992-09-02
Also published as: GB9104160D0

Abstract

A light modulator (1) for positioning adjacent a lens to regulate the light passing through the lens, comprising a plurality of leaves (7, 9) for defining an aperture (19) through which light passes, during use, and rotatable slide plate (5) with holes (15a) which accommodate drive pins so that when the plate is moved by moving handle (17) the pins cause the leaves (7, 9) to pivot about pivot pins (11) to vary the opening of the aperture (19), so that the aperture (19), forms arms (21) radiating outwardly from its centre to enable light passing through the aperture (19) to spread across the lens such that, when the positions of the leaves (7, 9) are altered, the light on the lens is evenly modulated. <IMAGE>

Description

A LIGHT MODULATOR This invention relates to light modulators, and in particular to a modulator which can be used to dim gradually and evenly a light source.

Luminaires for projecting images, slides and the like require a dimming facility, so that an image being screened can be illuminated with the optimum light intensity. Some projectors use tungsten or incandescent light sources, and the brightness of these can be controlled by adjusting the electrical voltage or current applied to the lamp. However, high intensity discharge lamps have many advantages over the aforementioned light sources, such as a four-fold increase in light output per watt and, more importantly, an output which spectrally matches "daylight colour" (i.e. the colour of normal daylight). Unfortunately, discharge lamps cannot be switched on and off or dimmed electrically with any degree of success. They have a warm up and a cool down period of 3-5 minutes and, when they are dimmed, the colour balance is distorted.Further, the discharge arc extinguishes itself at between 30-50% of the rated voltage.

It is therefore an aim of the present invention to provide means with which it is possible to produce a projector, incorporating a discharge lamp, which has a dimming facility.

A number of mechanical faders or dimmers are known, such as Venetian blind type shutters, iris diaphragms (as used in camera lenses) and comb shaped shutters.

Unfortunately these known faders all have drawbacks. For example, the Venetian blind type shutters and the comb shaped shutters both leave structure, which can image on the screen, in front of the light source even when the shutter is completely open. Further, iris diaphragms result in a high intensity spot in the middle of the lens, especially when the diaphragm has just opened and is allowing only a small amount of light therethrough. This also sharpens the image, which again is undersirable.

Accordingly, the present invention aims to overcome the drawbacks associated with the prior art shutters and faders, and to enable a controlled spread of light to be provided across a lens, thereby enabling a very even attenuation of the light to be achieved without affecting the image or the depth of field of the focus.With this in mind, there is provided a light modulator for positioning adjacent a lens to regulate light passing through the lens, comprising a plurality of leaves for defining an aperture through which light passes, during use, and drive means for moving the leaves between positions which vary the opening of the aperture, wherein the aperture, when defined, includes arms radiating outwardly from its centre to enable light passing through the aperture, during use, to spread across the lens such that, when the positions of the leaves are altered, the light on the lens is evenly modulated.

Preferably the leaves, when they are in a fully closed position, intermesh to close the aperture. Further, it is preferable that when the leaves are in a fully open position, they define an aperture through which light passes, during use, completely unhindered.

Preferably each arm of the aperture is defined by an opening between adjacent sets of leaves. Each arm preferably extends from the centre of the aperture to a radius which is substantially the same as the radius of the aperture when fully opened. In this way, as soon as the aperture is open, light may pass through the modulator at substantially all radii, thereby providing a degree of light on all parts of the lens.

The aperture, when defined, may have four arms.

However, if a light modulator were constructed with more or less leaves, a different number of arms may be defined.

The leaves are preferably divided into pairs, each pair including a front leaf and a back leaf. This arrangement enables the complete mechanism to be particularly compact, even when the aperture is fully open.

Each set of leaves preferably pivots about a single axis. The axis is preferably defined by a pivot pin mounted on a base plate.

The drive means preferably includes a slide plate which, during use, moves relative to the base plate to drive the leaves.

The drive means may include drive posts mounted on the slide plate for engaging and moving the leaves, during use.

The drive posts preferably engage in slots formed in each leaf, thereby enabling the aperture to be opened or closed in response to movement of the posts.

If each set of leaves includes two leaves, during opening of the aperture the inner leaf preferably moves first, before the two leaves begin to move together. This motion may be defined by the shapes of the slots in the leaves themselves.

Preferably the drive means may be activated remotely, possibly by adjusting a power supply to an electric motor acting on the slide plate. Alternatively, the slide plate, or other appropriate drive means, may be activated manually.

The leaves are preferably opaque. They may, however, be translucent and coloured, thereby acting as colour filters.

In accordance with a particular application of the present invention, there is provided a light projector comprising a light source, a lens and a light modulator according to the invention. Such a light projector may include more than one light modulator according to the invention, each modulator having translucent leaves of different colours. In this way, the projector can control the light intensity and colour of the film being screened.

A specific embodiment of the present invention is now described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic front view of a light modulator according to the present invention with its leaves in a closed position; Figure 2 is schematic front view as in figure 1, but with the leaves in a partially open position; Figure 3a is a front view of a base plate incorporated in the light modulator of figures 1 and 2; Figure 3b is a front view of a slide plate incorporated in the light modulator of figures 1 and 2; Figure 3c is a schematic front view of a back leaf incorporated in the light modulator of figures 1 and 2; and Figure 3d is a schematic front view of a front leaf incorporated in the light modulator of figures 1 and 2.

With reference to the drawings, a light modulator (1) according to the present invention comprises a base plate (3), a slide plate (5), four back leaves (7) and four front leaves (9). The light modulator (1) is held together as shown in figures 1 and 2 by means of pivot pins (11). Each pivot pin (11) passes through a hole (13a) in a front leaf (9), a hole (13b) in a back leaf (7), a slot (13c) in the slide plate (5) and a hole (13d) in the base plate (3). As will be appreciated, in the embodiment of light modulator shown in the accompanying drawings, four pivot pins (11) are required to hold the four pairs of back leaves (7) and front leaves (9) in communication with the base plate (3) and slide plate (5). Of course, if more or less than four pairs of leaves (7, 9) were utilised, a different number of pivot pins (11) would be required.

Four drive pins (not shown) extend through four holes (15a) in the slide plate (5). These drive pins slide in the four slots (15b) in the base plate (3), the slot (15c) in each back leaf (7) and the slot (15d) in each front leaf (9). The slide plate (5) is further provided with a drive handle (17) which is moveable between an open and a closed position.

The slot (15d - shown schematically as a line in figure 3d) in each front leaf (9) is shaped as a single curve. In contrast to this, the slot (15c - shown schematically as a line in figure 3c) in each back leaf (7) comprises two curves, the curve (15c')nearest its pivot hole (13b) being essentially the same shape, in a different orientation, as the corresponding portion of the slot (15d) of the front leaf (9). Due to this arrangement, as the drive handle (17) is moved from its closed position to its open position, each drive pin (not shown) is driven along the slots (15b, 15c and 15d) and results in outward movement of the front leaf (9), followed by outward movement of both the front leaves (9) and back leaves (7) together.

During rotation of the slide plate (5) relative to the base plate (3), the back leaves (7) and the front leaves (9), the pivot pins (11) pass back and forth along the slots (13c) in the slide plate (5).

As can be seen from the drawings, the back and front leaves (7, 9) have an arcuate shape which, when the leaves are in their fully closed positions (as shown in figure 1), enables them to intermesh to prevent any light passing through the light modulator (1). However, when the position of the drive handle (17) is adjusted, either manually or by means of an electric motor, the drive pins slide in the slots (15b, 15c and 15d) of the base plate (3), back leaves (7) and front leaves (9), thereby forcing the leaves to pivot outwardly about their pivot pins (11) (as shown in figure 2). As soon as an aperture (19) is defined between the leaves, it includes radially extending arms (21) which reach from the centre of the aperture to a radius which is substantially the same as the radius of the aperture when it is fully open.The shape of this aperture (19) ensures that light passing through the aperture, during use, strikes a neighbouring lens at essentially all radii of the lens, thereby providing a spread of light across the complete lens.

As stated above, due to the shapes of the slots in the leaves (7, 9), the front leaves (9) move first to define the aperture (19) before the back leaves (7) and front leaves (9) more together to complete the opening of the aperture.

When the leaves are in their fully open positions, a large aperture is provided which is not impeded by any part of the modulator, as is often the case in many of the prior art shutter devices.

Although it is envisaged that a light modulator according to the present invention will have leaves which are opaque, thereby preventing any light from passing, coloured translucent leaves may also be used. Hence, if, for example, three light modulators having different coloured leaves are incorporated in a projector, the colour of the light striking the lens (and therefore providing the picture on the screen) can be accurately controlled. If such a arrangement is utilised, clearly three primary colours would be preferred.

Finally, the slim shapes of the back leaves (7) and front leaves (9) enable the light modulator (1) to be very compact, because even when the aperture (19) is fully open the leaves do not extend far outside the base plate (3).

It will of course be understood that the present invention has been described above purely by way of example, and that modifications in detail can be made within the scope of the invention.

Claims

1. A light modulator for positioning adjacent a lens to regulate the light passing through the lens, comprising a plurality of leaves for defining an aperture through which light passes, during use, and drive means for moving the leaves between positions which vary the opening of the aperture, wherein the aperture, when defined, includes arms radiating outwardly from its centre to enable light passing through the aperture, during use, to spread across the lens such that, when the positions of the leaves are altered, the light on the lens is evenly modulated.

2. A light modulator as claimed in claim 1, wherein the leaves, when they are in a fully closed position, intermesh to close the aperture.

3. A light modulator as claimed in claim 1 or claim 2, wherein the leaves, when they are in a fully open position, define an aperture through which light passes, during use, completely unhindered.

4. A light modulator as claimed in any preceding claim, wherein each arm of the aperture is defined by an opening between adjacent sets of leaves.

5. A light modulator as claimed in claim 4, wherein each set of leaves pivots about a single axis.

6. A light modulator as claimed in claim 5, wherein the axis is defined by a pivot pin mounted on a base plate.

7. A light modulator as claimed in any preceding claim, wherein each arm extends from the centre of the aperture to a radius which is substantially the same as the radius of the aperture when fully open.

8. A light modulator as claimed in any preceding claim, wherein the aperture, when defined, has four arms.

9. A light modulator as claimed in any preceding claim, wherein the leaves are divided into pairs, each pair including a front leaf and a back leaf.

10. A light modulator as claimed in claim 9, wherein, during opening of the aperture, one leaf of each pair moves first, before the two leaves begin to move together.

11. A light modulator as claimed in any preceding claim, wherein the drive means includes a slide plate which, during use, moves relative to a base plate to drive the leaves.

12. A light modulator as claimed in claim 11, wherein the drive means includes drive posts mounted on the slide plate for engaging and moving the leaves, during use.

13. A light modulator as claimed in claim 12, wherein the drive posts engage slots formed in the leaves, thereby enabling the aperture to be opened or closed in response to movement of the posts.

14. A light modulator as claimed in any preceding claim, wherein the drive means is activated remotely.

15. A light modulator as claimed in claim 14, wherein the drive means is activated by adjusting a power supply to an electric motor.

16. A light modulator as claimed in any preceding claim, wherein the leaves are opaque.

17. A light modulator as claimed in any one of claims 1 to 15, wherein the leaves are translucent and coloured.

18. A light modulator substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

19. A light projector comprising a light source, a lens and a light modulator according to an preceding claim.

20. A light projector as claimed in claim 19, wherein more than one light modulator is provided, each modulator having translucent leaves of different colours.

21. A light projector as claimed in claim 19 or claim 20, wherein the light source is a discharge lamp.