DE9007798U1 - Camera viewfinder with a device for detecting the viewing direction of the eye of the user of the camera - Google Patents

Description

Camera viewfinder with a device for detecting the viewing direction of the eye of the camera user

The invention relates to a camera viewfinder according to the preamble of claim 1. Such a camera viewfinder is known from DE 38 41 575 A1.

One of the characteristics of the eye is the difference between a visual axis, which is the same as the direction of gaze, and an optical axis. Figure 3 is taken from Figure 44 on page 426 of "Behavior Research Methods & Instrumentation 1975, Volume 7 (5)." In Figure 3 it can be seen that the visual axis generally makes an angle of 5° to 7° with the optical axis.

The previously known viewfinder does not detect the direction of view, but the direction of the optical axis. This detected direction differs slightly from the direction in which the user looks at something.

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Another problem is individual scatter or variation. The previously mentioned angle difference is a statistical mean. If the individual scatter is taken into account, the angle has a scattered distribution. The distance kl between the pupil center and the center of curvature of the cornea also changes with the individual scatter.

Therefore, even if the difference between the visual axis and the optical axis is optically corrected, the difference may still exist due to individual variation. In addition, the difference between the two axes changes when the user wears contact lenses.

It is an object of the invention to improve a viewfinder of the previously known type in such a way that the difference between the optical axis and the visual axis is compensated for the respective user.

The invention solves this problem by the features of claim 1. Advantageous further developments are specified in the subclaims.

The invention enables the storage of personal correction data, which indicate the difference between a logical viewing direction and a viewing direction during observation, and the correction of a detected signal on the basis of the correction data.

The invention is described below using embodiments with reference to the drawing.

Fig. 1 is a schematic view of focus detection zones and judgment zones in a viewfinder of a first embodiment of the invention;

Fig. 2 is a schematic view showing the general structure of a gaze direction detecting device in the first embodiment;

Fig. 3 is a schematic view of the structure of the human eye; and

Fig.4

(a),(b),(c) are diagrams showing video signals without corrections, where Fig. 4(a) shows the case when a user looks at the point X = 0.00 mm, Fig. 4(b) the corresponding case at X = -9.00 mm, and Fig. 4(c) the corresponding case at X = +9.00 mm.

Figures 1 and 2 show an embodiment of the invention.

First, the structure is explained using Fig. 2.

In Fig. 2 are shown: a pentagonal prism 40 built into a camera, a quick-fold mirror 41, a focusing plate 42, a condenser lens 43, an eyepiece finder lens 44, a user's eye 45 and the optical axis AxO of the finder system.

This camera is equipped with three optical focus detection systems (not shown) equipped with CCD line sensors 71, 72 and 73.

Three focus detection zones 80, 81, 82 each corresponding to a viewing direction of the focus detection optical systems are arranged as shown in Fig. 1. The outer zone 80 has a first correction point 91 (X = +dX) at its center, and the zone 82 has a second correction point 92 (X = -dX) at its center. The correction points are used for setting the personal correction data.

However, the invention is not limited to placing the correction points in the image focus measuring zones.

A line of sight detecting optical system has a light emitting system 46 and a light receiving system 47. The light emitting system 46 directs a parallel light beam to an eye 45 of a user looking into the viewfinder. The light receiving system 47 detects light reflected from the eye 45.

The light emitting system 46 has an infrared light emitting diode 48, a total reflection mirror 49 and a collimator lens 50. Infrared light emitted by the light emitting diode 48 is reflected by the total reflection mirror 49 and directed onto the collimator lens 50. The collimator lens 50 is provided with an aperture 51 on its outward-facing side surface. The collimator lens 50 has the function of converting the infrared light emitted by the light emitting diode 48 into a parallel beam of rays.

On the side of the eye 45 and the viewfinder eyepiece lens 44, a light path overlapping optical element 52 is provided for overlapping the optical axis of the light beam system 46 and the optical axis of the light receiving system 47. The light path overlapping optical element 52 is a rectangular parallelepiped with prisms having a reflecting surface 53.

The reflecting surface 53 used in this embodiment is semi-transparent to infrared light and transparent to visible light. Since the reflecting surface 53 transmits visible light, the user can see an image of the object formed on the focusing plate 42. The parallel beam of rays passed through the aperture 51 is reflected by the reflecting surface 53 toward the eye 45 and projected onto it.

The light beam for forming the first Purkinje image by the corneal reflection of the eye 45 and the light reflected on the retina pass through the reflecting surface 53 of the light path overlapping optical element 52 and are then guided to the light receiving system 47.

The light receiving system 47 has a compensating prism 59, a reducing lens 60, a total reflection mirror 61, an imaging lens 62 and a CCD line sensor 63.

The eye 45 is typically located at an eye location. The CCD line sensor 63 and the pupil of the eye 45 are optically conjugated to each other by the viewfinder eyepiece lens 44, the reducing lens 60 and the imaging lens 62. The light reflected from the eye 45 forms a silhouette of the pupil and the first Purkinje image on the CCD line sensor 63.

The output signal of the CCD line sensor 63 is amplified by the amplifier 65 and then converted into a digital signal by an A/D converter 66. The digital output signal of the A/D converter 66 is input to a CPU 67 as a judging and selecting means and then temporarily stored in a RAM 68.

A setting switch 67a and a selection switch 67b are connected to the CPU 67. The setting switch 67a is used to set the personal correction data, and the selection switch 67b is used to select one of the correction data.

Regarding the angle of rotation θ formed between the optical axis of the viewfinder and the visual axis, the distance d between the center of the pupil and the first Purkinje image and the distance kl from the center of the pupil to the center of curvature of the cornea are expressed by the following equation:

d = kl · sinG

If sin9 is expanded by a Taylor series and approximated to the first expression, the following expression results for the previously mentioned equation:

d - kl · &thetas;

If an expression dO is included in the approximate equation as an offset of the distance d, the following equation results:

d = kl · θ + dO

The coefficients kl and dO are calculated based on two pairs of coordinates (Θ, d). The following explains how to set the coefficients.

The CPU 67 calculates the rotation angle θ on the basis of the distance d resulting from a video signal stored in the RAM 68 and the distance kl and the offset do which are selected and stored back from the E ² PROM (electronically erasable programmable ROM) 69.

The CPU 67 calculates the coordinates (X, Y) of the viewpoint at which the user is looking based on the rotation angle θ and judges which judgment zone he is looking at at the coordinate. In the case that the viewpoint is positioned in any judgment zone, the CPU 67 judges that the user selects the focus detection optical system corresponding to the focus detection zone in which the viewpoint is positioned. After the judgment, the CPU 67 outputs a selection signal to a drive circuit 70. The drive circuit 70 drives one of the CCDs 71, 72, 73 corresponding to the selected focus detection optical system.

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The focus detection device (not shown) detects the state of focus of the lens on an object. An automatic focusing device of the camera controls the lens so that it is focused on the object.

Video signals without corrections are described below.

Fig. 4(a), (b) and (c) show video signals under observation. An eye to be tested is the left eye wearing a contact lens. The abscissa indicates the amount of light and the ordinate indicates the number of bits of the CCD line sensor.

Figure 4(a) shows a video signal when the user looks at the center of the viewfinder, that is, the value of the X coordinate is 0.00 mm, and the line of sight detected based on the video signal is X = -4.22 mm. Furthermore, Figure 4(b) shows a video signal when the user looks at a point at X = -9.00 mm, and the line of sight detected is X = -13.11 mm. Figure 4(c) shows a video signal when the X coordinate is +9.00 mm and the line of sight detected is X = 4.67 mm.

This means that the result of the recording differs by -4 mm from the logical value to be recorded. However, it is not clear how great the influence of individual scattering or variation and the decentration of the contact lens is on the difference. At least it can be seen that the optical axis is tilted towards the minus side (one side of the ear) in the result.

Next, setting and selecting the correction data is explained.

A sequence of setting and selecting is performed by operating the setting switch 67a and the selection switch 67b. As previously mentioned, the coefficients kl, d0

in the case that they are values to be corrected in the above approximate expression, are determined by two solutions of (θ, d). The gaze direction detecting device determines the coefficients after finding coordinates under observation based on an output video signal when the user observes the first and second correction points 91 and 92. Before setting correction data, a middle or logical value is set as a standard value of the correction data.

When the user sets correction data, he looks at the first correction point 91 and pushes the setting switch 67a to ON. The CPU 67 calculates the coordinate of the viewpoint under observation. When the CPU calculates the coordinate, it calculates an average of detections to set a value to increase reliability.

Next, the user looks at the second correction point 92 and presses the setting switch 67a to ON again. The CPU 67 also calculates the coordinates of the viewpoint corresponding to the second correction point as in the case of the first correction point.

Further, the CPU 67 substitutes two coordinates for the approximate expression to calculate the coefficients kl, dO which are personal values of the user and stores them in the E ² PROM. Next, the CPU 67 writes an identification code in the E ² PROM in continuation of the address of the correction data to establish a relationship between the correction data and the user. The personal value is inputted with a switch provided on the camera or an input device connected to the camera.

In addition, the previously mentioned procedure requires two correction points.

However, the correction can also be achieved if at least the offset dO is recorded as a personal datum and the distance kl is treated as a fixed datum. In this case, a correction point in the viewfinder is sufficient. The CPU 67 calculates the value dO on the basis of the coordinate of the point of view at which the user is looking.

When the user operates the camera, he or she operates the selection switch 67b to select his or her correction data identifiable by the identification code. After selecting the personal data and finding out the gaze direction, the detection data is corrected with the user's personal correction data. The gaze direction detection device can accurately detect a gaze direction because detection variation caused by individual differences is avoided.

In the aforementioned embodiment, only the correction of the gaze detection in the X-axis direction was explained. However, it is clear that correction in the Y-direction can also be achieved. In the latter case, when two coefficients kl, dO are used as variables, four correction points are required, and when only the coefficient dO is used as a variable, two correction points are required.

In this embodiment too, a user sets his or her personal correction data and selects it from a variety of personal data. However, if the device can store only one person's correction data, the user sets his or her correction data when using the camera after it has been used by another user.

Claims (4)

- 10 protection claims 1. Camera viewfinder with a device for detecting the viewing direction of the eye of the user of the camera, with an optical system for detecting a first Pukinje image appearing at the eye at a distance d from the pupil center by means of an opto-electrical light detecting element, the output signals of which are fed into a computing circuit for calculating the angle &thetas; between the optical axis of the viewfinder and the visual axis of the eye from the relationship d = k} · sin9, with k]_ = distance between the pupil center and the center of curvature of the cornea, characterized by at least one correction viewpoint (91, 92) fixed in the viewfinder field of view or at least two correction viewpoints (91, 92) fixed in the viewfinder field of view, by a device (67, 67a) with a computing circuit for determining correction values dO as differences to normal values for the at least one fixed correction viewpoint (91, 92) or correction values dO and values for k^ as differences to normal values for the at least two fixed correction viewpoints (91, 92), by a memory (69) for the determined correction values and by taking the determined correction values into account when determining the directions of view. 2. Camera viewfinder according to claim 1, characterized in that two fixed correction viewing points (91, 92) are provided on either side of the center of the viewfinder image field. 3. Camera viewfinder according to claim 1 or 2, characterized in that a setting switch (67a) is provided for writing the determined correction values into the memory (69) together with an identification code of a specific user. - 11 - 4. Camera viewfinder according to claim 3, characterized in that a special input device is used to enter the identification code.