GB2451886A - Flash lamp diffusion unit for compact cameras - Google Patents

Abstract

An optical diffusion unit includes a diffusing member 1 that can obscure the flash lamp B to scatter light passing through it, a supporting member 2 with light shielding means such that stray light exiting the diffuser may not then directly enter any optical sensors C on a camera A, and attachment means for attaching the unit to the flash lamp window B of a compact stills camera A. The diffusing member 1 may be moved away from the flash lamp window B whilst remaining attached to the camera A. The diffusing member 1 may have properties for reducing the amount of high frequency blue light passing through it. The unit is intended for use on domestic compact stills cameras with built in flash lamps. It results in the reduction of overexposure and shadow contrast when taking photographs on compact stills cameras with the flash turned on.

Description

Flash lamp diffusion unit for compact cameras.

This invention relates to a device for diffusing light emitted by the flash lamps that are built into compact stills cameras.

When taking photographs in me absence of adequate lighting, the majority of compact stills cameras can emit a short burst of high intensity light from a built-in flash bulb. These cameras measure the brightness and/or distance of the main subject and set the amount of light emitted by the flash accordingly so as to achieve a proper exposure However, it is widely acknowledged that the light emitted by camera flash bulbs is rarely suitable for achieving aesthetically pleasing images. For example, in portrait photographs that are taken with the use of flash lighting, people's faces can often look older than in real life with skin wrinkles and eye sockets appearing darker and deeper. To overcome this, professional photographers routinely use equipment and techniques to diffuse the light that illuminates their subjects.

There is a tendency for manufacturers of compact cameras to strive for greater miniaturisation, so the maximum size of built-in flash lamps is limited. As a result, compact cameras harness as much of the potential light available from the flash by emitting it Predominantly perpendicular to the face of the flash window. This light is therefore Concentrated in a relatively narrow beam in order to effectively illuminate subjects at distances from the camera of over three metres. When this beam of light hits a relatively close subject, the camera rightly chooses an exposure value that renders the central subject correctly. However, the background may look unnaturally dark in comparison due to a lack of illumination towards the edges of the scene.

The use of flash lamp diffusion reduces this central concentration of the light as well as the contrast of shadows by scattering the light at more varied angles from the source, It improves the appearance of a subject by making facial and/or other shadows appear less defined and by giving the impression that a physically larger light source was used.

As well as suffering from normal flaws in the aesthetic appearance of flash lighting, compact cameras also have further technical shortcomings in this area. Most compact cameras have a macro mode which forces the lens into focussing on objects when they are closer than the normal minimum focus distance. When in this mode, a camera will often also attenuate the flash illumination level at the same time. A focus "crossover zone" exists within which a subject can be sharply focussed regardless of whether the camera is in the normal mode or macro mode. On some models this crossover zone is large enough to cause the following problem. A subject that is in the crossover zone may well be focussed while the camera is in the normal mode. However, the subject may be too close for the minimum flash output level that the camera uses in this mode, to work. The flash emits too much light and results in an over-exposed photograph. There is rarely an automatic switchover or indication that macro mode is recommended; it normally has to be triggered manually by activating a switch or menu setting. If macro mode is manually selected in this circumstance then the camera reduces the level of light outputted by the flash to compensate for the close proximity and often results in a correct exposure. A further problem associated with macro focussing is that when a subject is near to the minimum possible focal distance, the light level outputted by the flash can still be too great (even with automatic attenuation) and result in an over-exposed image.

Even when a scene is correctly exposed and focussed there is often an unnatural colour bias in flash-lit photographs. With regard to traditional film cameras, the film's emulsion is commonly balanced to record daylight (which has a nominal value on the colour temperature scale of 5600° Kelvin) as pure white in colour when reflecting off a pure white surface. With regard to digital cameras, their electronic processors line up the colorimetry of the image to ensure that correct white balance is achieved. When the built-in flash lamp (which also has a colour temperature of 5600°K) is engaged, the processors ordinarily line up with that value by default to give a neutral white balance.

Much flash photography is carried out indoors where we are used to seeing under "warmer" types of light (3200°K for tungsten bulbs, 4700°K for fluorescent). In photographs of this nature it is common to see these "warmer" light sources: either directly (such as a visible table lamp) or inthrectly (the light cast on a wall by such a lamp). Therefore, when a camera provides additional illumination with a flash lamp, the resulting images can took unnatural as the main subject locks too "cold" in comparison with the "warm" background. A common anecdotal complaint is that people with pale skin can look "washed out", sometimes prompting the operator to take another photograph with no flash at all which rarely gives a correctly exposed image.

To overcome all of these problems, the present invention proposes a flash lamp diffusion unit with attachment means for attaching the unit to a compact stills camera, and light-shielding means such that stray diffused light may not be permitted to directly enter any nearby optical sensors the camera may possess. The unit has a mechanism for quickly disengaging the diffusing member when the amount of light passing through it, as a result of its diffusing properties, is not sufficient for producing a properly exposed photograph.

The diffusing member may possess filtering properties for altering the spectral composition of the light that is transmitted through it, resulting in a small reduction of the higher frequency wavelengths. The overall shape of the unit and its attachment means are such that the unit can be effectively used on a wide range of compact cameras without impeding their performance or harming their exterior surfaces.

The invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure 1 shows an optical diffusion assembly attached to the flash window on the front of a compact camera, seen from the front elevation, Figure 2 shows an optical diffusion assembly attached to the flash window on the front of a compact camera, seen from the left side elevation, Figure 3 shows an optical diffusion member seen from the left side elevation, Figure 4 shows an optical diffusion member seen from the rear elevation, Figure 5 shows a supporting frame for accommodating an optical diffuser, seen from the front elevation, Figure 6 shows a supporting frame for accommodating an optical diffuser, seen from the plan view, Figure 7 shows an optical diffusion member attached inside a supporting frame, seen from the front elevation, Figure 8 shows an optical diffusion member attached inside a supporting frame, seen from the left side elevation, FIgure 9 shows an optical, seen from the front elevation, Figure 10 shows an optical diffusion member attached inside a supporting frame, seen from the left side elevation, Figure 11 shows an optical diffusion assembly attached to the flash window on the front of a compact camera with additional mechanical support, as seen from the front elevation, Figure 12 shows an optical diffusion assembly attached to the flash window on the front of a compact camera with additional mechanical support, as seen from the left side elevation, In figure 1, an optical diffuser 1 is mounted inside a supporting frame 2 which is attached so as to surround the flash lamp window B of a compact camera A. The diffuser is shown in an upward position, exposing the flash lamp window.

In figure 2, the diffuser is positioned downward to cover the camera's flash window and diffuse the light emitted from it. The supporting frame has shielding means to prevent stray light from escaping the diffuser and directly entering any optical sensors C on the camera. When light passes from the flash lamp, through the diffuser, it is scattered by reflections inside the diffusion material so that it exits at differing angles. This decentralises the beam of light, causing the desired attenuation and reduction in shadow contrast.

Figures 3 and 4 show suggested features of the diffuser that would allow it to move within the supporting frame. A radius creates a rounded edge 9 along the upper rear of the diffuser. A groove featuring a semi-tubular channel 6 is made along the top of the diffuser. Directly opposite, on the other side of the groove, is a ninety degree corner 7 which forms a sharper edge along the upper front of the diffuser. A bevel shape 8 running along the bottom edge allows the diffuser to close inside the supporting frame In figures 5 and 6, an axle shaft 3 is located towards the top of the supporting frame. The diffuser is attached to the supporting frame by pressing the groove of the diffuser against the axle shaft, so that the shaft clips into the tubular channel. The supporting frame has an aperture 5 at its centre which allows light to pass into the diffuser. The rear face of the supporting frame 11 is where attachment means 4 (which may take the form of an adhesive pad) can be positioned in order to attach the device to a camera. The other three sides of the frame form the light shielding means 10.

Figures 7 and 8 show the diffuser mounted inside the supporting frame in the active, downward position. In order that the camera flash can return to normal functioning with ease, a mechanism to disengage the diffuser is suggested. Applying pressure to the upper front edge 7 of the diffuser can cause it to pivot around the axle shaft 3. The action is aided by the rounded edge of the diffuser 9, which reduces resistance against the rear face of the supporting frame 11 during initial rotation. When the diffuser has rotated by ninety degrees there is resistance to further movement caused by the upper front edge 7 as it makes contact with the rear face of the supporting frame.

Lifting the bevelled lower edge 8 upwards can force the upper front edge to pass between the axle rod 3 and the rear face of the supporting frame, allowing the diffuser to end in the upward position and not fall back down under gravity.

Figures 9 and 10 show the device in the inactive state, after upward rotation of the diffuser by 180 degrees has been completed. When the diffuser is needed again it can be rotated downwards by degrees as described above. The bevelled edge 8 of the diffuser allows it to shut inside the supporting frame without hitting the lower part of the shielding means 10.

On some cameras, the flash is positioned or shaped in such a way that mounting the device using a normal attachment means 4 becomes less effective. One example of this type of problem, and how it may be overcome, is shown in figures 11 and 12. A compact camera A is shown which has a flash lamp window D sited very close to the top of the camera. Using normal attachment means 4 on its own would result in a lack of attachment at the top of the supporting frame. However, an attachment means 12 with triangular cross section and bonding surfaces would be able to create a firm attachment at the top of the supporting frame and reduce the risk of it being pulled away from the camera.

Claims (4)

1. Claims 1. An optical diffusion unit comprising a diffusing member that can obscure the flash lamp window of a compact stills camera to scatter any light passing through it, light shielding means such that stray light exiting the diffuser may not then directly enter any optical sensors on a compact stills camera, and attachment means for attaching the unit to the flash lamp window of a compact stills camera.
2. 2. An optical diffusion unit according to claim 1, in which the diffusing member may be moved away from the flash lamp window whilst remaining attached to the camera.
3. 3. An optical diffusion unit according to claim 1, in which the diffusing member has the necessary filtering properties for reducing the amount of high frequency blue light passing through it.
4. 4. An optical diffusion unit according to claim I in which the attachment means are versatile in their ability to attach the unit to a wide variety of compact camera flash lamp windows without detaching easily by accident or harming the surface of the camera.