JP2003029312A - Photometric device for automatic focusing camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a proper photometry result right after the focus of a photographic lens is adjusted when focus detection is carried out by lighting a subject with an auxiliary light. SOLUTION: The photometric device, used for an automatic focusing camera equipped with focus detecting means 15, 16, and 18 which detect the focus adjustment state of the photographic lens, a subject lighting means which lights the subject by emitting the auxiliary light for focus detection, and a focus adjusting means 21 which adjusts the focus of the photographic lens according to the focus detection result, is equipped with a charge accumulation type photoelectric converting means 16 which accumulates electric charges according to subject luminance in every set charge accumulation time and outputs an electric signal, a luminance arithmetic means 17 which computes the subject luminance according to the output of the photoelectric converting means 16, an accumulation time setting means 19 which sets the charge accumulation time so that the output level of the photoelectric converting means 16 reaches a predetermined proper level, and a storage means 20 which stores the charge accumulation time right before the auxiliary light is emitted; and the accumulation time setting means 19 sets a next charge accumulation time according to the charge accumulation time right before the fill-in light emission stored in the storage means 20 right after the auxiliary light of the subject lighting means is ceased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photometric device for an autofocus camera.

[0002]

2. Description of the Related Art There is known an autofocus camera which detects a focus adjustment state of a photographing lens by using a charge storage type sensor including a plurality of pixels such as CCD and automatically adjusts the focus of the photographing lens. Also known is a photometric device that measures the brightness of a field using a charge storage type sensor composed of a plurality of pixels such as a CCD (for example, Japanese Laid-Open Patent Publication No. H09-0909.
-257574 publication). Further, a technique is known in which a charge storage type sensor is used for both focus detection and photometry.

In the photometric device disclosed in Japanese Unexamined Patent Publication No. 09-257574, the charge storage time of the charge storage type sensor is shortened when the subject brightness is high, and the charge storage time is lengthened when the subject brightness is low. By doing so, control is performed so that an appropriate level of sensor output can be obtained regardless of subject brightness. The charge accumulation time is determined based on the charge accumulation time at the previous accumulation and the output level of the sensor obtained at that time.

On the other hand, when the brightness of the subject is low, the charge accumulation time becomes long in order to obtain the sensor output at a level suitable for focus detection, and the usability deteriorates. Therefore, an autofocus camera has been proposed that illuminates the subject with auxiliary light when the luminance is low to increase the luminance of the subject and enables focus detection in a short charge accumulation time.

[0005]

By the way, even in the above-described autofocus camera which detects the focus by illuminating the auxiliary light when the brightness is low, the auxiliary light is an obstacle when actually taking a picture, so the auxiliary light is turned off and the picture is taken without the auxiliary light. I do. Since shooting is performed without auxiliary light, the subject brightness for determining the exposure value at the time of shooting must also be measured without auxiliary light. In addition, it is desirable to set the time from obtaining the photometric result to the actual shooting as short as possible.Therefore, the auxiliary light is emitted to detect the focus, and after the focus of the shooting lens is achieved, the auxiliary It is necessary to set the sequence so that the light is turned off, photometry is performed, and the image is taken immediately.

However, when the focus adjustment of the taking lens is finished and the auxiliary light is turned off, the brightness of the subject suddenly drops. Therefore, the conventional method for determining the charge storage time of the next sensor, which determines the charge storage time of the next sensor based on the charge storage time at the previous storage and the output level of the sensor, is the same as the conventional method for determining the charge storage time. When applied to a camera, an appropriate charge accumulation time cannot be set immediately, and the charge accumulation operation is repeated several times until a sensor output of an appropriate level is obtained. Therefore, since the photometric time becomes long, the time from the end of the focus adjustment to the shooting becomes long, the feeling of use deteriorates, and a photo opportunity may be missed.

An object of the present invention is to provide a photometric device for an autofocus camera which can obtain an appropriate photometric result immediately after the focus adjustment of the taking lens is finished when the subject is illuminated with auxiliary light to perform focus detection. Especially.

[0008]

The present invention will be described with reference to FIGS. 1 and 2 showing the configuration of an embodiment. The present invention is based on a focus detecting means 15 for detecting a focus adjustment state of a photographing lens. 16, 18 and subject illuminating means 13, 14 for illuminating the subject by lighting auxiliary light for focus detection,
A photometric device for use in an autofocus camera including focus adjusting means 11 and 21 for adjusting the focus of a taking lens 3 based on a focus detection result, wherein a charge corresponding to a subject brightness is set for each set charge accumulation time. Is stored and outputs an electric signal, a charge storage type photoelectric conversion means 16, a brightness calculation means 17 for calculating subject brightness based on the output of the photoelectric conversion means 16, and an appropriate output level of the photoelectric conversion means 16 is predetermined. Is provided with a storage time setting means 19 for setting the charge storage time so that the charge storage time is set to a high level, and a storage means 20 for storing the charge storage time immediately before the auxiliary light is turned on. Immediately after the auxiliary light is turned off, the next charge accumulation time is set based on the charge accumulation time stored in the storage unit 20 immediately before the auxiliary light is turned on. Further, in the photometric device of the autofocus camera according to claim 2, the photoelectric conversion means 16 causes the accumulation time setting means 1 to operate.
The electric charge is accumulated by the electric charge accumulation time set immediately after the auxiliary light is turned off by 9, and the luminance calculator 17 calculates the subject luminance based on the output of the photoelectric converter 16.

In the section of means for solving the above-mentioned problems, the drawings of one embodiment are used for the sake of easy understanding of the description, but the present invention is not limited to this embodiment. .

[0010]

1 is a cross-sectional view of an autofocus camera of one embodiment. A replaceable lens barrel 2 is attached to the camera body 1. The light flux from the subject is guided to the main mirror 4 of the camera body 1 through the taking lens 3. A part of the light flux from the subject is reflected by the main mirror 4 and guided to the finder 5, passes through the screen 6, the pentaprism 7 and the eyepiece lens 8 and is guided to the photographer's eyes, and the screen image is observed by the photographer. To be done.

Another part of the light flux from the subject passes through the main mirror 4 and is reflected by the sub-mirror 9 to be guided to the photometric focus detection section 10 as a light flux for photometry and focus detection. The photometric focus detection unit 10 detects the defocus amount and the subject brightness indicating the focus adjustment state of the taking lens 3 based on the output of one charge storage type sensor. The motor 1 is based on the detected defocus amount of the taking lens 3.
1 is driven and controlled, and the taking lens 3 is moved in the optical axis direction so as to be in focus. At the time of photographing after the focus adjustment, the main mirror 4 and the sub-mirror 9 are retracted from the photographing optical path toward the finder 5, and the photographing lens 3 forms a subject image on the silver salt film or the image sensor 12. When the brightness is low, the LED 13 is caused to emit light, and the auxiliary light is emitted to the subject through the light projecting lens 14 to illuminate the subject.

FIG. 2 shows the detailed structure of the photometric focus detection section 10. The focus detection optical system 15 guides the subject light flux reflected by the sub-mirror 9 to the charge storage sensor 16, and forms a pair of subject images on the pair of pixel rows of the charge storage sensor 16. The charge storage sensor 16 has a pair of pixel rows composed of a plurality of pixels, and the focus detection optical system 1
An electric signal corresponding to the light intensity distribution of the pair of subject images formed by the image sensor 5 is output. The photometric calculator 17 calculates subject brightness based on the output of the charge storage sensor 16 and the charge storage time. The focus detection calculation unit 18 calculates a defocus amount indicating the focus adjustment state of the taking lens 3 based on the output of the charge storage sensor 16. The detailed calculation contents of the photometry calculation unit 17 and the focus detection calculation unit 18 are well known, and thus the description thereof will be omitted.

The charge accumulation control unit 19 sets a charge accumulation time for adjusting the output level of the charge accumulation sensor 16 to an appropriate level, and performs charge accumulation control. For example, if the maximum value Pk is obtained among the plurality of pixel outputs in the charge storage time IT, the charge storage time IT is updated by the following equation.

## EQU1 ## IT = IT.Po / Pk where Po is the target maximum level. In this embodiment, the maximum value is used as an example, but the charge storage time may be determined using, for example, the average value of a plurality of pixel outputs.

The storage time storage unit 20 is a memory for storing the charge storage time immediately before lighting of the auxiliary light. The motor drive control unit 21 drives and controls the motor 11 based on the defocus amount calculated by the focus detection calculation unit 18. The auxiliary light emission control unit 22 emits light from the LED 13 according to the subject brightness calculated by the photometric calculation unit 17, and controls turning on and off of the auxiliary light.

FIG. 3 is a flowchart showing the overall operation of the photometric focus detection section 10. While the shutter release button of the camera is half-pressed, the photometric focus detection unit 10
The operation shown in FIG. 3 is repeatedly executed. That is, the initial operation (step 1) shown in detail in FIG. 4, the intermediate operation (step 2) shown in detail in FIG. 5, and the end operation (step 3) shown in detail in FIG. 6 are sequentially and repeatedly executed.

The initial operation of the photometric focus detection section 10 will be described with reference to FIG. In step 101, a predetermined initial value is set as the charge accumulation time IT because there is no previous accumulation result in the first charge accumulation. In the following step 102, the charge accumulation control unit 19 accumulates charges in the charge accumulation type sensor 16 to obtain an output. In step 103, the maximum value of a plurality of pixel outputs is detected and set as Pk.
In step 104, it is determined whether the maximum value Pk is within a predetermined reference range, and it is confirmed whether the output level of the charge storage sensor 16 is appropriate. When the sensor output is at the proper level, the process proceeds to step 106, and when it is not at the proper level, the process proceeds to step 105. If the sensor output is not at an appropriate level, the charge accumulation control unit 19 calculates the charge accumulation time I according to Equation 1 in step 105.
T is updated, and the process returns to step 102 to charge again.

On the other hand, when the sensor output is at an appropriate level, in step 106 the photometric calculator 17 calculates the subject brightness based on the sensor output and the charge storage time IT. In step 107, the subject brightness calculated by the photometric calculation unit 17 is compared with the brightness of a predetermined determination reference,
When the subject brightness is lower than the determination reference value, it is determined that auxiliary light irradiation is necessary. If the auxiliary light irradiation is required, the process proceeds to step 108, and if not necessary, the process proceeds to step 115. If the auxiliary light irradiation is unnecessary, the focus detection calculation unit 18 calculates the defocus amount of the taking lens 3 using the sensor output of an appropriate level in step 115.

If auxiliary light irradiation is required, step 10
In step 8, the charge storage time IT calculated in step 106 immediately before turning on the auxiliary light is stored in the storage time storage unit 20 as ITp. In the following step 109, the LED 13 is caused to emit light by the auxiliary light emission control unit 22 and the auxiliary light is emitted to the subject.
In step 110, the charge accumulation control unit 19 anticipates an increase in the brightness of the subject due to the auxiliary light emission, and the charge accumulation time IT
Is shortened at a predetermined rate. In this embodiment, it is shortened to 1/4. In step 111, the charge accumulation control unit 19 performs the accumulation operation of the charge accumulation sensor 16 and inputs the charge accumulation data for each pixel.

In step 112, the maximum output value among a plurality of pixel outputs is detected and set as the maximum value Pk. Then, in step 113, it is determined whether or not the maximum value Pk is within a predetermined determination reference range, and it is confirmed whether or not the output level of the charge storage sensor 16 is appropriate. If it is determined that the output level of the sensor 16 is not appropriate, step 11
In 4, the charge accumulation control unit 19 updates the charge accumulation time IT by Formula 1, and returns to step 111 to accumulate charges again.

On the other hand, if it is determined that the output level of the charge storage sensor 16 is appropriate, then in step 115 the focus detection calculation unit 1 is used by using the sensor output of an appropriate level.
8, the defocus amount of the taking lens 3 is calculated. This completes the initial operation.

As described above, since the photometric calculation is always performed once before the auxiliary light emission, the photometric result can be obtained immediately after the start of the photometric and focus detection operations. A camera having a function of displaying a photometric result can display the photometric result immediately after the start of the photometric and focus detection operations.

The intermediate operation of the photometric focus detection section 10 will be described with reference to FIG. In step 201, it is determined whether the defocus amount calculated by the focus detection calculation executed in step 115 of the initial operation or the focus detection calculation executed in step 209 of this intermediate operation is within a predetermined focus determination reference range. A determination is made to see if the taking lens 3 is in focus. If the taking lens 3 is in focus, this intermediate operation is terminated, and if it is not in focus, the process proceeds to step 202.

The motor 11 is driven and controlled by the motor drive controller 21 based on the defocus amount calculated in step 202. In the following step 203, the charge accumulation control unit 19 performs the charge accumulation operation of the charge accumulation sensor 16 and inputs the charge accumulation data for each pixel. In step 204, the maximum output value of the plurality of pixel outputs is detected and set as the maximum value Pk. In step 205, it is determined whether the maximum value Pk is within a predetermined reference range, and it is confirmed whether the output level of the charge storage sensor 16 is appropriate. If the output level of the sensor 16 is an appropriate level, the process proceeds to step 207, and if not, the process proceeds to step 206.

If the output level of the charge storage type sensor 16 is not an appropriate level, the charge storage control unit 19 updates the charge storage time IT by using Equation 1 in step 206, and the process returns to step 203 to restart charge storage. To do.
On the other hand, when the output level of the sensor 16 is an appropriate level, it is confirmed in step 207 whether or not the auxiliary light is being lit. When the auxiliary light is lit, it is not necessary to perform the photometric calculation. If it is skipped and the auxiliary light is not lit, a photometric calculation is performed in step 208. That is, the photometric calculator 17 calculates the subject brightness based on the output of the charge storage sensor 16 and the charge storage time IT. Next, in step 209, the focus detection calculation unit 18 performs focus detection calculation using the sensor output of the appropriate level obtained by the charge accumulation in step 203, and the defocus amount of the taking lens 3 is calculated. Then, the process returns to step 201 and the focus determination is performed again.

As described above, since the photometric calculation is not performed when the auxiliary light is turned on, the result obtained in step 106 during the first operation is held as the photometric result, and the subject brightness is increased by turning on the auxiliary light. However, this does not cause a problem that the photometric result changes.

The ending operation of the photometric focus detection section 10 will be described with reference to FIG. In step 301, it is confirmed whether or not the auxiliary light is on, and if it is not on, the ending operation is ended, and if it is on, the process proceeds to step 302. In step 302, the auxiliary light emission control unit 22 controls the LED 1
3 is turned off and the auxiliary light irradiation is stopped. Continued Step 30
In step 3, the charge storage time ITp stored in the storage time storage unit 20 immediately before lighting of the auxiliary light is set as the storage time IT.

In step 304, the charge accumulation control unit 19 performs the charge accumulation operation of the charge accumulation type sensor 16, and the charge accumulation data for each pixel is input. Continued Step 305
Then, the maximum output of a plurality of pixel outputs is detected and set as the maximum value Pk. In step 306, it is determined whether the maximum value Pk is within a predetermined reference range, and it is confirmed whether the output level of the charge storage sensor 16 is appropriate. If the output level of the sensor 16 is an appropriate level, the process proceeds to step 308, and if not, the process proceeds to step 307. If the output level of the charge storage sensor 16 is not an appropriate level, the charge storage control unit 19 updates the charge storage time IT by using Equation 1 in step 307, and returns to step 304 to store the charge again. On the other hand, when the output level of the sensor 16 is an appropriate level, the photometric calculation unit 17 calculates the subject brightness based on the output of the charge storage sensor 16 and the charge storage time IT in step 308. With this, the ending operation is completed.

The time for illuminating the subject by illuminating the auxiliary light for focus detection is short, and it is considered that the brightness of the subject does not change significantly before and after the illumination of the auxiliary light. The charge accumulation time at the time of acquisition is stored, read immediately after turning off the auxiliary light, and set as the previous charge accumulation time. Based on this, the next charge accumulation time is set to immediately obtain an appropriate sensor output. It is possible to obtain an accurate photometry result immediately after focusing of the taking lens.

In this embodiment, an example in which the photometric sensor and the focus detection sensor are used in common is shown, but the present invention can be applied to an autofocus camera equipped with a charge storage type sensor dedicated to photometry. .

[0030]

As described above, according to the present invention, even when the subject is illuminated with the auxiliary light to detect the focus and the focus of the photographing lens is adjusted, the charge immediately before the auxiliary light is turned on after the focus adjustment is completed. An appropriate next charge storage time can be set based on the storage time, and the output of the photoelectric conversion unit at an appropriate level can be obtained immediately after the focus adjustment is completed. Therefore, even when the auxiliary light is turned on, an accurate photometric result can be obtained immediately after the focus adjustment is completed, and the image can be taken immediately.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an autofocus camera according to an embodiment.

FIG. 2 is a block diagram showing details of a photometric focus detection unit of the autofocus camera according to the embodiment.

FIG. 3 is a flowchart showing the overall operation of the photometric focus detection unit according to the embodiment.

FIG. 4 is a flowchart showing an initial operation of the photometric focus detection unit according to the embodiment.

FIG. 5 is a flowchart showing an intermediate operation of the photometric focus detection unit according to the embodiment.

FIG. 6 is a flowchart showing an ending operation of the photometric focus detection unit according to the embodiment.

[Explanation of symbols]

10 Photometric focus detector 13 LED 14 Projection lens 15 Focus detection optical system 16 Charge storage type sensor 17 Photometry calculator 18 Focus detection calculation unit 19 Charge accumulation controller 20 Storage time storage 22 Auxiliary light emission control unit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 5/232 G02B 7/11 N 5/235 G03B 3/00 A (72) Inventor Hiroyuki Iwasaki Chiyoda, Tokyo Ward Marunouchi 3 2-3 No. F-term in Nikon Corporation (reference) 2H002 DB00 DB02 DB06 DB08 DB20 DB24 FB84 GA54 HA04 HA05 HA11 JA02 2H011 DA01 DA08 2H051 EB02 EB19 5C022 AA13 AB04 AB05 AB15 AB17 AB28 AC32 AC74

Claims (2)

[Claims] 1. A focus detecting means for detecting a focus adjustment state of a photographing lens, a subject illuminating means for lighting auxiliary light for focus detection, and a focus adjustment of a photographing lens based on a focus detection result. A charge accumulating photoelectric conversion means for accumulating electric charge according to subject brightness at each set electric charge accumulation time and outputting an electric signal. A brightness calculation means for calculating the subject brightness based on the output of the photoelectric conversion means, and an accumulation time setting means for setting the charge accumulation time so that the output level of the photoelectric conversion means becomes a predetermined appropriate level. A storage unit that stores the charge storage time immediately before the auxiliary light is turned on, and the storage time setting unit stores the charge immediately after the auxiliary light of the subject illumination unit is turned off. A photometric device for an autofocus camera, characterized in that the next charge storage time is set based on the charge storage time immediately before lighting of the auxiliary light stored in the means. 2. A photometric device for an autofocus camera according to claim 1, wherein the photoelectric conversion means accumulates electric charges for the electric charge accumulation time set immediately after the auxiliary light is turned off by the accumulation time setting means, The photometric device for an autofocus camera, wherein the brightness calculation means calculates subject brightness based on an output of the photoelectric conversion means.