TECHNICAL FIELD:

The present invention relates to a method and a device for surveying light conditions upon photographing.

TECHNICAL PROBLEM:

When photographing outdoors, the work of the photographer is complicated by the changing lighting conditions. For instance, the sunlight may change due to clouds, and displacement of objects around the subject may affect the illumination of the subject.

TECHNICAL BACKGROUND:

In these conditions, the photographer may adjust his exposure settings according to different methods. He may measure incident light towards the subject, see for example WO 81/03385. Alternatively, from the camera he may measure the light reflected from the subject. In the latter case, he may utilize integral measurement, implying that the result of a measurement becomes a type of average value of the light reflected from the entire subject, or from parts of it. Alternatively, the photographer may utilize so- called spot measurement, wherein a limited angle of incidence is utilized.

When performing spot measurement, the reflected light from different parts of the subject is measured. The exposure values are thus usually determined from the measurement on the most significant part of the subject (e.g. a face, a flower). After the exposure values have been determined in

this way, however, it often happens that the photographer makes adjustments, for example lightens up a shadow by means of a reflector or artificial light. These measures should of course normally not affect the exposure of the significant portion of the subject.

During the time period when the photographer makes his adjustments, however, a change of the incident light may have taken place, for example due to cloud changes. Since slow changes of the incident light are difficult to detect with the naked eye, the exposure may easily become incorrect after the adjustments by the photographer.

SUMMARY OF THE INVENTION:

The object of the present invention is to avoid said unintended incorrect exposures.

Said object is achieved by means of the method and the device according to the present invention, whereby the intensity of the incident or reflected light is detected at a certain moment, stored and indicated as reference information. After this detection moment, deviations from the reference information are detected and indicated, whereby the photographer is informed of changes before exposure takes place.

BRIEF DESCRIPTION OF THE DRAWINGS:

In the following, the invention will be explained in greater detail with reference to the attached drawings, in which

Fig. 1 shows an example of an application in which the method and the device according to a first embodiment are utilized,

Fig. 2 shows an example of a surveying device according to the first embodiment, wherein the device is completely detached.

Fig. 3 is a side view of a viewfinder, which is detachable from a camera, into which a surveying device, according to a second embodiment of the invention, is integrated,

Fig. 4 schematically shows the surveying device in the viewfinder according to Fig. 3, mounted on a camera, whereas

Figs. 5-10 show a display integrated into the device, which is shown in different stages of the lighting surveillance.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS:

The method according to the present invention is most advantageously illustrated with an example of an application as shown in Fig. 1, wherein a model is photographed outdoors. In this situation, the lighting conditions may rapidly change radically, for instance, by means of the sun going behind a cloud after the photographer has prepared the photographing. The preparation work, inter alia, includes that the exposure values are determined e.g. by means of spot measurement towards the face of the subject, by means of an exposure meter, which is either separate or integrated into the camera. The method according to the invention implies that the light measurement system of the camera is supplemented

with a system for detecting the incident light at a certain moment, for example the moment when the photographer has determined the exposure values, whereafter this information is stored and deviations from the stored value thereafter are detected and indicated to the photographer. In the example shown in Fig. 1, according to a first embodiment, the method is accomplished by means of a separate device 1 for exposure surveying. This device can thus be placed in the vicinity of the subject in order to detect the light towards the subject. The surveying device 1 is thereby arranged to communicate in some way with the camera 2 of the photographer, or at least with the photographer, in order to provide him with information about deviations in the lighting conditions. In a more advanced design, both the surveying device 1 and the camera can be provided with means for emitting, as well as receiving, information regarding the exposure conditions, which information will be described in greater detail below. This communication may be constituted by wire communication, i.e. by means of a wire connection between the surveying device and the camera, or wireless communication, for example via radio, infrared light, ultrasonics, etc. In less complicated cases, the communication can be limited to an acoustic signal, which is emitted from the surveying device 1 to the photographer when certain preset deviations are reached and exceeded. The surveying device is of course placed so that it is not visible in the field of view.

Fig. 2 shows in greater detail an example of the construction of an entirely separate, i.e. detached, surveying device 1 for the exposure conditions. The device is designed with a resistant casing 3, which suitably is designed with a lower portion 4, forming a support against a basis 5, so that the device can be placed upright with a detector cell 6, for example built-in in a transparent, dulled half-sphere for incident light, facing upwards and

suitably placed on the upper side 7 of the device. The device is provided with a display or an indication window 8 which clearly provides information concerning the exposure conditions with visual symbols, e.g. with numerical information about chosen exposure values EV, or time of exposure-aperture combination. According to the invention, the display displays a symbol 9, containing information about a chosen reference 10, in the example in the form of a 0-point, and information about deviation from the reference value along a scale 11, see below for closer details with reference to Figs. 5 - 10.

The device further exhibits a number of manually operable control means, arranged in the casing 3, intended for adjustment of the surveying device, namely a lock button 12 for activating the surveying device and locking the reference information at a certain moment when the exposure values have been determined during the preparation work.

Furthermore, the device exhibits means for inputting and determining limits for said deviations in the light intensity. These means include an activation button 14 for activating and deactivating the limit function, and a correction button 14 for changing interval limits upwards or downwards. The device further comprises an audible alarm 15, which is activated when the limits are exceeded.

Figs. 3 and 4 show the device in a second embodiment, integrated into a viewfinder 16, which is detachably attachable to the viewfinder plate 17 on a camera 2 of reflex type.

As is evident from Fig. 3, the same type of control means as in the first embodiment is present in the viewfinder design, which control means are arranged in the casing 18 of the viewfinder. Accordingly, the lock button 12, the

activation button 13 and the correction button 14, having the above-described functions, are all present.

The surveying device, which in principle is a type of light meter, is advantageously integrated with an exposure meter for detecting the exposure values valid for the photographing. The viewfinder design thereby provides a possibility to switch between different measurement methods, such as spot measurement, integral measurement, and measurement of incident light, in all three cases of which the surveying device can be connected. These different measurement methods or programs can be scrolled by means of a program button 19. Further adjustment possibilities affecting the choice of exposure values are selection of the largest aperture with a selection button 20 and of film sensitivity with a selection button 21. Otherwise, as in the first embodiment, the detector cell 6 for incident light positioned on the casing 16, whereas the indicating window 8, which is shown in an entirely symbolic way in Fig. 4, can be observed in the viewfinder, which in a conventional way exhibits an eyepiece 22, attachment means 23 for attachment of the viewfinder to the viewfinder plate 17, and a viewfinder hood 24, facing the viewfinder, for allowing entry of the light beam 27, reflected through the lens 25 in the camera and via the mirror 26.

In Fig. 4, the integrated functions of the surveying device are illustrated in an entirely schematic way. The function for the three exposure programs, controlled by the program button 19, is illustrated with a block 28 for program selection to which, except the program button 19, detectors 19 for the three exposure types are connected. The measurement cell 6 for incident light comprises a detector 29 placed in such a way, under a suitably dulled, transparent dome 30, that light may reach directly into the detector with an angle of incidence of up to 180°. Inside

the viewfinder hood, a second detector 31 for integral measurement is placed, whereas a third detector 32 is placed behind a refractive lens 34 for reducing the angle of incidence, which in intended to be activated in the program position for spot measurement. The special functions of the surveying device are collected in a block 35, which thus comprises the above-mentioned means for storing exposure values at a certain given moment, and for activating and correcting a limit for deviation from the exposure value, locked at a certain moment. The display 8, which may have the same appearance as in Fig. 2, is connected to this function, as is described in greater detail below. The blocks 28, 35 are suitably realized in the form of microelectronics, such as a programmable microprocessor.

With reference to Figs. 5 and 10, the method upon photographing, with utilisation of the surveying device, will now be described. The appurtenant display 8 may either display detected EV-value, see Fig. 5, or the combination of time and aperture it corresponds to, see Fig. 6. The deviation from a pre-set reference value is symbolized with an additional scale symbol 36 below the fixed scale 9, which is described below.

The method of operation is as follows:

The photographer measures the prevailing light and, guided by the presented EV-value or time of exposure/aperture combination, he adjusts the time of exposure and aperture on the camera. Thereafter, he stores a reference value by means of activating the lock button 12 and pressing it for, for example, two seconds, whereby previous reference values are deleted. As a confirmation of a value being stored, for instance, a short audible signal may be emitted. The scale now shows deviation 0 (zero), see Fig. 7, which is symbolized with a central scale division 37 placed at 0.

When the device is set for measuring incident light and a change of the incident light occurs, for example when the sun goes behind a cloud, a change of the EV-value from for example 12 to 11 takes place, see Fig. 8. This deviation is symbolized with the additional scale symbol 36, which in this case has an extension identical to one unit in a negative direction.

According to the invention, there is a possibility to set a desired limit for deviation of the exposure value from the reference value by means of the activation button 13 and the correction button 14. These warning limits or alarm limits are set symmetrically around 0 by means of the correction button 14, and are indicated with scale divisions 38, 39 on each side of the 0-value.

Fig. 10 shows a situation in which the deviation has been achieved and the predetermined limit has been exceeded, since the exposure value has decreased by two steps, wherein a warning or an alarm is emitted, for instance, by means of the scale in the display blinking or, for example, by means of an audible signal being activated.

The display, shown schematically in Fig. 4, acts as a character window to the observer in the viewfinder, for example in the lower or upper portion of the field of view, whereby the photographer during the preparation work, when he is observing the subject through the viewfinder, obtains instantaneous information concerning deviation. The display may display further symbols, for example a symbol for each exposure program. A symbol 40, for selection of program for incident light measurement, is shown to the right in Figs. 5-10.

The invention is not limited to the embodiments described above and shown in the drawings, but may be varied within

the scope of the following claims. For instance, the limit function may be omitted entirely and the deviation can be symbolized in another way.