Fuji Photo Optical Co., Ltd.

Fujinon Corporation

Yoshikazu Mihara

Hideo Yoshida

In a rangefinder, if sensor data initially received by a sensor data storage part from an A/D converter includes data with low contrast, the sensor data storage part receives the sensor data at least one additional time, adds additionally received sensor data to the initially received sensor data, and stores their sum. In accordance with the sum of sensor data stored in the sensor data storage part, a correlation calculation and a rangefinding calculation are carried out, which enables rangefinding with respect to an object having low contrast; Also, the time required for A/D-converting the sensor data again and adding the resulting data to those initially obtained is much shorter than the integration time required for integrating output signals of a pair of line sensors a second time for a region with low luminance and low contrast.

Rangefinder apparatus

A distance measurement object is imaged by a pair of line sensors of an AF sensor, and sensor data showing the sensor images is generated. A CPU generates AF data showing the contrast of sensor images with the sensor data being sequentially acquired by the CPU for each cell. Then, the AF data is used to carry out calculation of correlation values or the like, thereby calculating the distance from the distance measurement object. Thus, generation of AF data for distance measurement calculation such as correlation value calculation showing the contrast of the sensor images formed by the pair of line sensors of the AF sensor, and distance measurement calculation using the AF data are carried out by the computation processing circuit (CPU) to simplify the circuit, and also the sensor data is sequentially acquired from the AF sensor, and at the same time the AF data is sequentially generated, whereby the amount of processing time for generation of the AF data is significantly reduced to shorten distance measurement time.

Distance measuring apparatus using passive AF sensor

Correlation value calculation is carried out while a pair of window ranges being shifted using uncorrected AF data, and a pair of window ranges providing the highest correlation value is determined. Then, the difference between the smallest values in the respective window ranges is evaluated. If it is determined that the distance is large, the AF data is corrected so that the smallest values in the respective window ranges are consistent with each other, and the corrected AF data is used to carry out correlation value recalculation. Then, if the highest correlation value after correction is smaller than the highest correlation value before correction, the result of correlation value calculation after correction is employed.

Distance measuring apparatus

A rangefinder apparatus includes an effective minimum value certifying unit for comparing a minimum value, exhibiting the smallest value in correlation values calculated for the each rangefinding area, with a reference value for a degree of correlation and certifying a minimum value smaller than the reference value as an effective minimum value, effective for a rangefinding calculation, a distance calculating unit for calculating the distance to the object according to the effective minimum value certified for each rangefinding area; and a correlation calculation restricting unit for omitting the correlation calculation within a specific distance range, farther by at least a predetermined amount than the shortest distance calculated according to the effective minimum value in the correlation calculation for a rangefinding area to be later subjected to the correlation calculation, when the effective minimum value exists in the rangefinding area earlier subjected to the correlation calculation.

In the distance measuring apparatus which uses a passive AF sensor and determines the subject distance by carrying out correlation value calculation according to AF data obtained from a pair of line sensors of the AF sensor to detect the smallest minimum value of the correlation value, if the difference between the smallest minimum value and the second smallest minimum value of the correlation values is smaller than a predetermined value, it is determined that distance measurement is impossible, and the predetermined value is changed in accordance with the magnitude of the smallest minimum value, thus making it possible to appropriately determine whether distance measurement is possible or impossible according to the aspect of AF data. Therefore, problems such that it is determined that distance measurement is impossible more than necessary, or erroneous distance measurement occurs can be prevented. Also, if the distance object is located at a distance shorter than the closest distance at which distance measurement is possible, it is determined that distance measurement is impossible, and/or a short distance warning is given, so as to prevent erroneous distance measurement.

In multi-point distance measurement, the distance of a distance measurement object is three-way divided into a very short distance range, a short distance range and a moderate to long distance range, and if the distance of an object located at a very short distance is measured in any one of the endmost distance measurement areas of a plurality of distance measurement areas, and all the distances measured in other distance measurement areas belong to the moderate to long distance, the distance belonging to the very short distance range is not employed, and the shortest distance of distances belonging to the moderate to long distance range is employed as a measured distance. On the other hand, if any of the distances measured in other distance measurement areas belongs to the short distance range which is closer than the moderate to long distance range, the distance belonging to the very short distance range is employed, thereby reducing the frequency of erroneous distance measurement. If of five distance measurement areas including left, left middle, middle, right middle and right areas, the left area corresponds to the very short distance range, and other distance measurement areas correspond to the moderate to long distance range, for example, the distance in the moderate to long distance range is employed as the measured distance.

The camera is capable of appropriate judgment as to whether or not an auxiliary light is to be emitted according to a luminance of a subject to be focused on by basing that judgment on a sensor output used in auto-focusing control. The camera is also capable of judging whether or not an auxiliary light is needed in a short period of time by setting a sensor sensitivity at a high level and of accurate auto-focusing control by setting the sensor sensitivity at a low level when an auxiliary light is to be emitted. When a shutter release button is half pressed, first an R sensor and an L sensor, which are passive type range finding devices are set at high sensitivity to shoot the subject, and a time taken to obtain a prescribed sensor output is measured. According to a length of time so measured, it is judged whether or not to emit an auxiliary light for auto-focusing use. If the auxiliary light is to be emitted, the sensor sensitivity is set at a low level and the subject is shot again to determine the subject distance on the basis of the sensor output at the time.

Camera with auxiliary light emission and auto-focus

In the distance measuring apparatus, it is determined whether or not a pair of AF data obtained by a pair of employed sensors indicate a first predetermined necessary contrast, and a correlation value calculation is performed only when the contrast is detected. Then, it is determined whether or not the AF data in a pair of window ranges where the highest correlation is obtained in a correlation value calculation indicate a second predetermined necessary contrast. Only when it is determined that there is the contrast, the subsequent process such as a calculation of the distance from a distance measurement object is performed. Thus, an unnecessary correlation value calculation can be possibly omitted at a low contrast level. Furthermore, erroneous measurement of distance can be avoided.

Where a subject is dark, half pressing of a shutter release button causes an auxiliary light for auto-focusing use to be emitted from an electric flash. If half pressing and cancellation take place consecutively, a power of a main capacitor for the electric flash will become in sufficient, it is charged after emission of an auxiliary light. A camera is to be provided which can prevent charge processing from deteriorating an operating convenience by limiting either a duration of charging or a charging voltage then. Where the subject is dark, half pressing of the shutter release button causes the electric flash to emit an auxiliary light (AF pre-emission) and auto-focusing control to be executed. If half pressing of the shutter release button and its cancellation take place consecutively, charging of the main capacitor of the electric flash is performed alternately for different lengths of time, 150 ms and 300 ms.

Camera

The sensor sensitivity and the method of setting the peak selected area of the AF sensor are changed according to the luminance level of the distance measurement object. The distance measuring apparatus uses a passive AF sensor to determine the distance of a distance measuring object by sensor data obtained from the AF sensor, wherein: if the distance measurement object has high luminance, the sensor sensitivity is set at low sensitivity, the distance measurement area is divided into three areas, and sensor data is acquired for each area as a peak selected area of the AF sensor; if the distance measurement object has moderate luminance, the sensor sensitivity is set at low sensitivity, and sensor data is acquired with the entire area of the distance measurement area being the peak selected area of the AF sensor; and if the distance measurement object has low luminance, the sensor sensitivity is set at high sensitivity, and sensor data is acquired with the entire area of the distance measurement area being the peak selected area, whereby proper sensor data is acquired to carry out distance measurement suitably and reliably.

A correlation value calculation is performed by using AF data arranged at predetermined intervals in the AF data in a pair of window ranges, so that a frequency of calculation can be reduced. On the other hand, a correlation value calculation is performed by using all the AF data in the pair of window ranges only in predetermined ranges before and after the shift amount of the pair of window ranges when the highest correlation value in the correlation values is obtained, thereby suppressing a reduction in measurement precision. For example, in a pair of the AF data obtained from a pair of window ranges, the correlation value calculation is performed by using every third piece of the AF data. Then, the correlation value calculation (normal calculation) is performed by using all the AF data in the pair of window ranges in predetermined ranges (range for re-performing the calculation) before and after the shift amount of the pair of window ranges when the highest correlation value is obtained in the correlation values obtained by the former correlation value calculation.

In the distance measuring apparatus, a passive AF sensor is used in which signals outputted from cells of a pair of line sensors are integrated for each cell to generate sensor data and an integration start signal is outputted upon start of integration, and when the peak value of the sensor data reaches an integration end value, an integration end signal is outputted. If the integration end signal is not outputted even after predetermined time elapses after integration is started in the AF sensor, the peak value of the sensor data is read to determine whether the integration is normally carried out. If the integration is not normally carried out, it is determined that distance measurement is impossible. If the integration is normally carried out, the sensor data is acquired from the AF sensor to carry out distance measurement thereby lessening the likelihood that it is determined that distance measurement is impossible more than necessary. The distance measuring apparatus comprises the passive AF sensor and a CPU which carries out various kinds of control of the AF sensor and calculation of the distance from a distance measurement object according to AF data acquired form the AF sensor. Whether or not integration is normally carried out is determined by the CPU with the integration end signal.

When the reflectance of an object at a distance to be measured is low and when the distance to the object is far, these conditions are discriminated and the distance is measured with a clamp signal set at a low level, thereby enhancing distance measurement accuracy. First a distance measurement is carried out with the clamp signal set at a high level. When the first distance value is larger than a predetermined distance, a second distance measurement is carried out with the clamp signal set at the low level. Then it is determined whether the second distance value is larger than a set value. When the second distance value is larger than the set value, the clamp signal is set to the high level and third a distance measurement is carried out. When the second distance value is not larger than the set value, on the other hand, the clamp signal is set to the low level under certain conditions and the third distance measurement is carried out.

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Saitama, Japan

Yoshikazu Mihara