DE3005043A1 - AUTOMATIC FOCUSING INDICATOR FOR A CAMERA - Google Patents

Description

HOFFMANN · ExTIiJE Oc PARTNER

DR. ING. E. HOFFMANN (1930-1974). DIPL.-I NG. W. EITLE DR. RER. NAT. K. HOFFMANN · Dl PL.-ING. W. LEH N

DIPL.-ING. K. FDCHSLE ■ DR. RER. NAT. B. HANSEN ARABELLASTRASSE 4 (STAR HOUSE). D-8000 MD NCH EN 81 TELEPHONE (08?) 911087. TELEX 05-29619 (PATHE)

33 061/2 s / cd

Asahi Kogaku Kogyo Kabushiki Kaisha, Tokyo / Japan

Automatic focus indicator for a camera

The invention relates to an automatic focus display device, in the in the focus position a focus indication signal is generated, indicating that the image of an object in question by a photographic Lens is properly focused.

A variety of cameras with automatic focus have been proposed for optical imaging systems, in which a correct focusing position is automatically determined so that the lens is in the focusing position can be moved. However, to date there has not been an automatic focusing single-lens reflex camera practically used through trade. An important reason

030033/0805

this is that a single lens reflex camera is a high quality camera, which in terms of the accuracy of the Determining the focus makes extremely strict requirements. There is also the lens of a single lens reflex camera is relatively heavy, the lens drive necessarily becomes large. After all, it's about stopping the photographic Lens in the focus position requires processing circuitry to provide who makes the decision whether the lens is just in front of or behind the focus position is located. The processing circuitry required for this is quite complex. These factors make the manufacture difficult with a single-lens camera with automatic focus.

A focus determination method is already known, in which, similar to a coincidence seeker working with a double image, the extent of a relative Shift between two optical images is detected electrically. Furthermore, there is a focus determination method known, in which a contrast information is taken from the image of an object to be photographed and a maximum value of the Contrast signal is detected.

The latter method uses the fact that the optical intensity or the power spectrum of each Spatial frequency of the image of an object to be photographed reaches a maximum at the time of focusing. In particular In this method, a serial position scanning output signal is obtained which is a measure of the brightness The distribution of the image is represented by the image with a

030033/0805

photoelectric converter element mechanically or electrically is sampled and the signal obtained in this way for the purpose of extracting high frequency components, namely the Contrast information, is differentiated. After the DifferentLabion signal is converted into an absolute value waveform the peak value of the absolute value waveform is extracted in a single sampling period and used as a focus signal.

A so-called "automatically focusing camera" can be built in which the photographic lens is automatic is moved depending on the focus signal described above. If a signal is also used, which is a measure of the focus position, it is also possible to use an automatic focus display device to create in which a light emitting element / such as a lamp, at the focus position is switched on.

Recently, a method has been proposed in which a self-scanning photoelectric conversion element is used as a Scanning device is used. The use of a self-scanning photoelectric conversion element makes it compact Scanning part possible. Therefore, the focus display device obtained according to this method can be used without difficulty in the arrangement of a single-lens reflex camera can be installed. That from the self-scanning photoelectric conversion element delivered signal is a maximum in the focus position. However, due to the presence of multiple objects within of the field of view of the photographic lens, more than one peak value can be obtained. Hence it is necessary to make the photographic

030033/0805

3QQ5Q43

Holding the lens in the focus position is a device to provide which makes the decision whether a peak value represents a real maximum. To this Purpose so far either two photoelectric conversion elements have been used, which are on the optical axis to both Sides of the focussing plane were arranged or a memory circuit for comparing the signals for two lens advance divisions were provided.

Efforts have been made to determine the correct focus position with high accuracy and to extract a digital signal corresponding to a single level that accurately indicates the focus position. However, as soon as an automatic focus indicating device is used in which a light emitting element is built in the camera which is operated in the focus position, the indication of the focus position with a focus signal of extremely high accuracy leads to other difficulties. The recording process occurs frequently _; while the camera is held in the photographer's hand. In this case, the camera is easily moved by the photographer's hand and, as a result, it is difficult to accurately focus the lens on the subject. Therefore, if a focus signal with extremely high display accuracy is used, the display of the signal can be turned on and off, making it difficult for the photographer to use the camera properly. On the other hand, in the case of images captured by a stationary camera, it is desirable to obtain high display accuracy of the focus. These two contradicting conditions affect cameras of high quality, such as single-lens reflex cameras, very significantly. This is a big reason why it is difficult to build a camera with an automatic focus indicator.

030033/0805

The invention is therefore based on the object of an automatic

To provide a table focus display device in which all of the aforementioned difficulties are eliminated and in which a focus signal with a high focus display accuracy is obtained when the camera is fixed in their position, but the focus signal has a lower focusing accuracy when the Camera is hand held.

An automatic focus display camera using a focus display device according to the present invention has has the considerable advantage that the in-focus position can be easily detected even when taking pictures with that of Hand-assisted camera can be recorded, while with stationary camera the focus indication with high accuracy he follows.

The invention is also intended to provide a simple focus display device can be created in which the contrast signal is immediately converted into a sound signal without that a complicated lens drive is used, so that the position of the photographic lens at which the desired Peak value reached a maximum by listening to the frequency or Amplitude change of the audio signal is determined. The device specifically uses the characteristics of the hearing, according to which it is possible to detect extremely small changes in tone, as well as the highest frequency or highest amplitude such tone changes. An essential feature of the invention Focus display device thus resides in coping with the difficult conditions of focus display accuracy can suffice that are required for a single-lens mirror camera.

030033/0805

The object on which the invention is based, mentioned at the outset is controlled by an automatic focus indicator solved for a camera having a photoelectric focusing signal detection device, which is actuated depending on the image of an object to be photographed in order to send an electrical signal generate which reaches a maximum value at the focusing position of a photographic lens of the camera, a display control means for generating a focus signal in response to the electrical signal when the photographic lens is located essentially in the focus position, and a display device that depends on the Focus signal works and in which a display state is dependent on the size of the focus signal changed that the display device is operated in a first mode to indicate that the photographic Lens is located within a predetermined focus position range while in a second Mode of operation indicates that the photographic lens is in the focus position. The display device may be a light emitting element whose brightness is controlled by the focusing signal. Furthermore, the Display device be a tone generator, for example a tone transducer, with at least the frequency or amplitude of the tone generated by the tone generator can be controlled by the focus signal. In the second mode of operation, either a zero or minimum frequency of the tone or a maximum frequency of the tone can be used.

According to one embodiment of the invention, the stated object and other objects on which the invention is based are achieved by a focus indicator

030033/0805

/ IO

§043

for a camera having a photoelectric conversion element for scanning the image of an object to be photographed to generate a serial position signal · which is a measure of the brightness distribution of the image, a Contrast determination circuit for taking a brightness signal in a high spatial frequency range, the brightness signal represents a measure for the image contrast, a circuit for converting the output changes of the contrast signal in frequency changes and a tone generator that works depending on the circuit, with the frequency of the sound supplied by the sound generator is at a peak value in the focusing position of the photographic lens of the camera. The amplitude of the generated sound can be changed in the Focus position be a maximum. Likewise, the peak value of the frequency of the tone can either be as desired Be a minimum or a maximum.

The invention will then be explained with reference to the drawings. Show it:

Figures 1A and 1B

graphic representations relating to the generation of a focusing signal in an automatic according to the invention Focus indicator,

Figure 2

a block diagram of a first embodiment of an inventive automatic focus indicator ,

030033/0805

Figure 3 shows a curve of the contrast signal in a circuit according to the invention, depending on Lens feed,

Figure 4 shows a series of waveforms representing the various stages of motion of the photographic Represent lens,

FIG. 5 shows a graphic illustration to explain the procedure in which the focusing signal is produced according to the invention,

FIG. 6 is a block diagram of a second embodiment of the automatic according to the invention Focus indicator,

Figure 7 is a block diagram of a third embodiment of the automatic focus display device for a camera according to the invention and

FIG. 8 shows a graph showing the frequency of the display signal generated as a function of the contrast of the object under consideration.

The invention will then be described in connection with the drawings. Figures 1A and 1B are graphical Illustrations indicating the generation of a focus signal in an automatic focus indicator. In particular, FIG. 1A shows the generation of a focusing signal according to a known method. The focus signal is used as a digital pulse

030033/0805

generated when the photographic lens is in a relatively narrow area S, which extends to both sides of the focus position. On the other hand, according to the present invention, the focus ^{signal is generated in a relatively wide area JL 1} which is located on both sides of the focus position. Furthermore, in accordance with the invention, the focus signal is changed in such a way that it has its maximum value when the photographic lens is in the focus position (focus position).

There now becomes a preferred embodiment of the invention in connection with one based on contrast detection Focus detection device described. Figure 2 shows an embodiment of a device in which a contrast signal based on the image of a object to be photographed. The image of an object 1 to be photographed is on a self-scanning photoelectric converter assembly 3 by a photographic Lens 2 received. The self-scanning photoelectric Converter arrangement consists of a plurality of photoelectric converter elements and a scanning circuit. In the converter arrangement the brightness distribution of the object image is scanned electrically in order to generate a time-series signal that the Corresponds to brightness distribution. The self-scanning photoelectric conversion device 3 is controlled by a control circuit which has a sampling pulse generator circuit to generate a discrete time-series waveform corresponding to the To deliver brightness distribution of an object image. -The waveform is after amplification by an amplifier circuit 5 with the help of a sample and hold circuit 6 into an analog

030033/0805

3001043

Waveform converted. The analog waveform obtained in this manner is supplied to a smoothing circuit 7, in which unwanted high frequency components from the analog waveform to be removed. Thus, the smoothing circuit 7 supplies a waveform which corresponds to the original brightness distribution of the object image. The waveform output by the smoothing circuit 7 is differentiated by a differentiating circuit 8, whereby a differentiation signal is obtained which represents a measure of the high spatial frequency of the image, ie the increase in the brightness distribution is indicated. The differentiation signal is converted into a positive or negative waveform by an absolute value circuit 9. The peak value of the output absolute values supplied by the absolute value circuit 9 for each sampling period is detected by a peak value detection circuit 10 and held until the next peak value is detected in the subsequent sampling period. The peak values obtained in this way form the aforementioned contrast signal. The contrast signal has its maximum value (amplitude) at the focusing position, ie when the photographic lens is in the focusing position indicated in FIG.

The focusing signal, which according to Fig. 1A changes digitally at the focusing position, can be used by using it in accordance with a method in which the maximum value of the contrast signal is stored once and when the contrast signal again reaches the stored fourth, a coincidence signal is generated. FIG. 4 is a diagram for a description of this method. In particular, the upper part of FIG.

030033/0805

Changes in the contrast signal, while the middle part of Fig. 4 shows the movements of the photographic lens, viz Indicates advance, retract and stop. The two parts of Fig. 4 illustrate the case in which the lens, the is initially in a stop position, is advanced, when the contrast signal reaches the maximum value, the lens is pushed back and when the contrast signal again reaches the maximum value, the lens is stopped. The first The maximum value of the contrast signal is stored and the contrast signal has the maximum value stored in this way compared. If the two values are the same, the aforementioned focusing signal is generated. Through the dash-dotted Line in the upper part of FIG. 4 indicates the stored peak value level. The lower part of Fig. 4 shows that, when the stored peak value coincides with the contrast signal, the focus signal is generated. A light emitting element can be switched on in digital mode using the focus signal.

The invention can be accomplished using the foregoing Contrast signal can be applied. Fig. 5 illustrates how the focus signal is generated in accordance with the invention. In particular, the upper part of FIG. 5 shows changes in the contrast signal, while the middle part of FIG. 5 shows the movements of the photographic lens similar to the case of FIG indicates. The photographic lens is stopped when the contrast signal, as in the case of FIG. 4, reaches its maximum value. It however, it should be noted that when the contrast signal reaches its maximum value, a value is stored which is subsequently is referred to as "voltage division peak value" and is smaller than the maximum value. The contrast signal is with compared to the voltage division failure value thus stored

030033/0805

* ^S I0OSOA3

and a focus signal is generated when the contrast signal is greater than this value. If the circuit is constructed in such a way that the focus signal changes accordingly the difference between the contrast signal and the stored value, the focusing signal can be taken. Of the The lower portion of Fig. 5 shows the focus signal generated in this way.

An example of an automatic focus indicator according to the invention is shown in FIG. The image of an object to be photographed 11 is on a for Contrast detection serving photoelectric converter arrangement 13 imaged by a photographic lens 12 in a similar manner, as described in connection with FIG. The output signal of the transducer arrangement 13 is sent to a contrast detection circuit 14 supplied, whereby a contrast signal is generated at the output of the transducer arrangement 13. the Contrast detection circuit can be a device according to FIG. However, it can also be a direction, a single one Contrast signal takes from the image of an object to be photographed.

The peak value of the contrast signal is detected by a peak value holding circuit composed of an operational amplifier A-. , a diode D., a resistor R ₁ and a capacitor C ₁ . The peak value hold signal, which occurs at the output of the peak value hold circuit, is _{subjected to a voltage division by resistors R "and R" after passing through a buffer amplifier, which is provided as operational amplifier A 2} , and the difference between the next following contrast signal and the voltage division peak value is taken through a differential amplifier which is fed by a

030033/0805

κ-

<f (t> 3QQ5Q43

Operational amplifier A _{3 is} formed. The output signal of the differential amplifier is a control signal which makes a transistor T .. conductive when the contrast signal is higher than the voltage division peak value. If the differential output signal of the differential amplifier increases, the current flowing between the collector and the "" emitter of the transistor T _{1 increases.} When the transistor T ₁ becomes conductive, current flows in a light-emitting diode D ₂ , which turns it on.

The peak value is stored in capacitor C. The capacitor C ₁ is discharged by operating an analog switch S ₁ which is controlled by a reset pulse from a reset pulse generator 15, whereby the peak hold signal is reset. This reset operation is necessary before the image of another object comes into focus. The jerk pulse can be generated in connection with the actuation of the shutter release button at the time of actuation of the shutter. The light-emitting diode is thus switched on when the photographic lens is essentially in the focusing position and the brightness of the light-emitting diode reaches its maximum value at the focusing position.

Another embodiment of the automatic according to the invention Focus indicating device in which focus is indicated by a sound signal is shown in Figs shown.

The device according to FIG. 7 has a so-called U / F converter 11 in order to convert voltage changes into frequency changes, and an amplifier circuit connected to the U / F converter 11.

030033/0805

If the of «a peak value detection circuit IO increases If the voltage value is held, the frequency of the tone supplied by a tone generating converter 13 increases. the The frequency of the generated tone is thus that of the peak value detection circuit 10 held voltage proportional. If an oscillator control circuit 14 between the U / F-ümsetzer 11 and the amplifier 12 inserted, it is possible to intermittently generate a tone signal with the tone generator, or a plurality of tone signals of different tone coloration. If at the focus indicator Changes in the tone amplitude are used, the peak value detection circuit 10 is connected to an oscillator circuit, which in turn is connected to an amplifier circuit, so that the gain of the amplifier circuit by the output of the peak value detection circuit is controlled.

The mode of operation of the device according to FIG. 7 will now be explained in more detail in connection with FIG. When looking at the The photographer pushes the edge-shaped part of the brightness distribution of an object within the focal area of the viewfinder the photographic lens 2 forwards or backwards. If the lens 2 is in the focusing position, 8, the frequency of the tone generated by the tone generator is the highest. The frequency is according to curve 15 at high object contrast, and according to curve 16 at low object contrast. The higher the contrast of the object, the greater the frequency change of the from Sound generator supplied sound. This means that when the contrast of an object is increased, the lens can effortlessly focus on the object can be focused. However, the lens can also be focused on a low contrast object because of the frequency

030033/0805

of the sound provided by the sound generator at the focus point becomes highest. This is a particularly advantageous feature of the focus display device according to the invention, which uses a sound signal generated at the focus position.

As can be seen from the preceding description, the light-emitting element in the device according to the invention turned on at the focus position and the focus signal reaches its maximum value in the position of correct focus. Furthermore, the focus indication signal gives the Photographers get a clear indication even when the camera is hand-held and yet has the focus indication signal very high display accuracy when the camera is held stationary.

In addition, the lens can be precisely focused on an object using only the maximum frequency value of the Tongeneratorwandler supplied tone is determined. Consequently is in a camera incorporating the focus display device of the present invention used, no usual laborious focus adjustment required. Because the edged Part of the brightness distribution of an object is determined, the lens can also be focused on a deep object. The sound generating element may be a piezoelectric buzzer that requires little space, or an earpiece.

In the device of Fig. 7, the contrast signal becomes immediate converted into an audio signal, so that the focus is determined on the basis of changes in the audio signal. the The device thus constitutes an acoustic focus indicator It goes without saying that the

030033/0805

acoustic focus indicator effective with a variety of visual focus indicators, for example a light emitting diode can be combined. Although with the tone generator circuit described above A tone with a maximum frequency at the focus point can also be a minimum or zero frequency be used.

In a case where. no further focusing is required, for example when photographing the same object repeatedly is, the sound signal generated by the sound generating element can disturb the photographer and it can in such Trap to be switched off. Thus, it is a combination of an acoustic focus indicator and a visual one Focus display device very advantageous.

In summary, the invention is an automatic Focus indicator has been created that is particularly suitable for use with a single lens reflex camera is suitable and in which a contrast signal is generated by taking the image through the photographic lens of the camera viewed object is scanned. This signal is converted into a display signal, which is either an acoustic signal or visual signal. When moving the lens to positions near the focus point, the display device operated in a first way. If the lens is exactly at the focus point, the display device will operated in a second way. In this way, the camera is well suited for both hand-held, as well as with the camera held stationary.

030033/0805

-ZO-

Blank page

Claims (9)

14ITlJS o £ PARTNER DR. ING. E. HOFFMANN (1930-1976). Dl Pl.-I NG. W. EITLE DR. RER. NAT. K. HOFFMANN · D IPL.-ING. W. LEH N DIPL.-ING. K. FDCHSLE DR. RER. NAT. B. HANSEN ARADELLASTRASSE 4 (STERN HAUS) D-8000 MO NCH EN 81 TELEPHONE (089) 911087 TELEX 05-29619 (PATH E) 33 061/2 s / cd Asahi Kogaku Kogyo Kabushiki Kaisha, Tokyo / Japan Automatic focus indicator for a camera Patent claims: 1 J Automatic focus indicator for a camera, characterized by a photoelectric working focus signal detection device, the works depending on the image of an object to be photographed to generate an electrical signal which has a maximum value at the focusing position of a photographic lens reached by the camera, a display for generating a Focusing signal, depending on the electrical signal when the photographic lens is substantially in the Focus position is located, and an indicator that depends 030033/0805 from the focus signal works, changing the display state the display changes depending on the magnitude of the focus signal in such a way that the display in a first operating mode is operated to indicate that the photographic lens is within a predetermined range of the Focus position is and wherein the display indicates in a second mode that the photographic lens is in the focus position. 2.. Automatic focus indicator 'according to Claim 1, characterized in that the display has a light-emitting element, the brightness of which is controlled by the focus signal. 3. Automatic focus display device according to claim 1, characterized in that the Display contains a tone generator and that at least the frequency or amplitude of the tone generated by the tone generator by the Focus signal can be controlled. 4. Automatic focus indicator after Claim 3, characterized in that the second mode of operation by a minimum frequency of the sound is pictured. 5. Automatic focus display device according to claim 3, characterized in that the second mode of operation by a maximum frequency of the sound is pictured. 030033/080 5 6. focus indicator for a camera, characterized by a photoelectric converter arrangement (3) for scanning the image of a photographing object to generate a time-series signal that represents the brightness distribution of the image, a contrast detection circuit (14) for extracting a brightness signal in a high spatial frequency range, wherein the luminance signal represents a contrast of the image, a circuit for converting the output signal changes of the contrast signal in frequency changes and a tone generator that works depending on the circuit, the tone frequency generated by the tone generator at the focusing position of a photographic lens of the camera Peak value reached. 7. focus display device according to claim 6, characterized in that the amplitude of the tone generated by the tone generator has a maximum at the time of focusing. 8. focus display device according to claim 6, characterized in that the peak value is a minimum. 9. focus display device according to claim 6, characterized in that the peak value is a maximum. 030033/0805