JP2013130757A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a deviation of a focusing position caused by an influence of various aberrations of a lens, in a lens adjustment stage for a dimensional tolerance, etc., in manufacturing a lens.SOLUTION: An imaging apparatus includes diaphragm control means which is diaphragm control means 117 controlling diaphragm means 103 restricting a luminous flux made incident through a zoom lens 102 performing variable power and a focus lens 105 adjusting a focus and correcting a change of a focal plane position caused by the variable power and restricts the open amount of the diaphragm means according to the position of the zoom lens, storage means which is storage means 120 storing information of the relation between the zoom lens and the focus lens for each subject distance and stores information of a focusing position relationship in such a state that the open amount of the diaphragm means is restricted by the diaphragm control means, and adjustment means which detects the focusing position of the focus lens to adjust the reference positions of the zoom lens and the focus lens, in such a state that the open amount of the diaphragm means is restricted according to the position of the zoom lens.

Description

  The present invention relates to an imaging apparatus that adjusts a focus position relationship between a zoom lens and a focus lens in a lens system having a diaphragm.

FIG. 10 shows a simple configuration of a general rear focus type lens system.
In FIG. 10, 101 is a fixed first lens group, 102 is a second lens group (zoom lens) for zooming, 103 is a stop, and 104 is a fixed third lens group. Reference numeral 105 denotes a fourth lens group (focus lens) having both a focus adjustment function and a so-called compensator function for correcting movement of the focal plane due to zooming, and 106 is an image sensor such as a CCD. As is well known, in the lens system configured as shown in FIG. 10, the focus lens 105 has both a compensator function and a focus adjustment function, so that the imaging surface of the image sensor 106 is focused even if the focal lengths are equal. Therefore, the position of the focus lens 105 varies depending on the subject distance. Even if the subject distance is the same, if the focal length is changed by the zooming operation, the focus lens position for focusing is different. Then, when the zoom lens is driven and the zooming operation is performed for each subject distance, the position of the focus lens 105 for focusing on the imaging surface is continuously plotted as shown in FIG. . In FIG. 11, the horizontal axis indicates the zoom position, that is, the focal length, and the vertical axis indicates the focus lens position. During zooming operation, if any of the trajectories shown in FIG. 11 is selected according to the subject distance and the focus lens 105 is moved according to the trajectory, the zooming operation without blurring becomes possible. .

  In the control of the rear focus type lens system, the lens control microcomputer in any form (the locus itself or a function with the lens position as a variable) may be used as the locus information (cam locus information) based on the optical design values in FIG. Remember me. In general, a locus is selected and specified according to the positions of the focus lens and the zoom lens, and zooming is performed while following the selected locus. However, in an actual lens system, cam trajectory information is created based on optical design values, but in reality, when manufacturing a lens, there is a dimensional tolerance in each component of the lens, or a lens barrel. The mounting dimension tolerance of the position with respect to. For this reason, this locus is not as designed, and when zooming is performed, a focus shift occurs.

  Therefore, usually, in the adjustment stage after manufacture, the amount of focus deviation is detected for each manufactured product, and the correction amount calculated from the detected amount of deviation is stored in, for example, the nonvolatile memory of the control circuit of each product. In this way, the focus is not shifted. As an adjustment method, as described in Patent Document 1, the stroke of the zoom lens from the tele end to the wide end is kept as designed, and the focusing position of the focus lens at the tele end and the wide end at an adjustment distance (for example, infinite) is used. The difference (balance) is also determined to be the design value. In addition, find the zoom lens position where the focus lens reaches the highest point on the path at the middle (intermediate focal length) and the zoom lens position where the amount of movement from the focus lens position at the tele end is the design value. There is known a so-called tele-middle tracking adjustment method for setting the position of the zoom lens. Furthermore, after adjusting by the above method, a so-called cam that detects the amount of deviation between the actual in-focus position at the adjustment distance and the position on the designed cam locus at a plurality of zoom positions and calculates it as a correction amount. A correction adjustment method is also known.

Japanese Patent No. 4072224

  In the conventional adjustment method as shown in Patent Document 1, when the focus position is obtained by moving the focus lens or the zoom lens, the aperture is set so that the depth of focus becomes shallow in order to ensure the detection accuracy of the focus position. Control to the most open state (mechanical open state) on the mechanical mechanism. Then, the focus position is determined based on the sharpness (AF evaluation value) of the video signal, and the reference position is determined by detecting the amount of deviation from the designed cam trajectory information in the mechanical open state, and the cam correction amount is calculated. It was common to do.

  However, the lens has various aberrations, especially spherical aberration, at the periphery, so that the accuracy of the spherical surface at the periphery of the lens can be improved with an inexpensive lens that suppresses the production cost of mass production or an ultra-small and ultra-high magnification lens. difficult. For this reason, at some focal lengths, spherical aberration may deteriorate when the diaphragm is opened, or the resolution may be reduced due to the phenomenon of flare. Therefore, the adjustment is performed including the shift of the in-focus position due to the influence of the above. On the other hand, in the actual camera control, at the focal length where the aberration is bad, the control is performed to reduce the influence of the aberration in the lens peripheral portion by limiting the opening amount of the aperture, and from the in-focus position including the influence of the aberration. There is a problem that determining the reference position or calculating the cam correction amount does not match the actual control.

  In addition, when the aperture is changed, the focus position gradually changes due to the influence of aberration around the lens. For example, when the aperture is changed with the focus lens position fixed by the manual focus lock (MF) function. Corrects the focus lens position in accordance with the aperture amount. This is so-called aperture focus correction control. In this aperture focus correction control, conventionally, the amount of deviation between the in-focus position when the aperture is in the mechanical open state and the in-focus position when the aperture is set to the predetermined aperture amount (F value) is obtained from design data, measured values, and the like. In advance, correction values such as table data are stored. Then, the focus lens position is moved by the correction value according to the aperture amount.

  However, the mechanical opening position of the aperture varies depending on the dimensional tolerances of the components of the aperture and the mounting tolerances during assembly, especially for low-cost lenses that are low in manufacturing costs and ultra-small, ultra-high magnification lenses. Tolerances and mounting tolerances vary greatly compared to conventional lenses. For this reason, the in-focus position in the mechanical open state also varies greatly. Even if the focus lens is moved by the correction value obtained from the design data or the like in that state, there remains a correction residue. If the focus lens is bad, the correction correction amount exceeds the depth of focus, so that it appears as blur.

  In order to reduce the aberration in the lens peripheral portion as described above, it is necessary to increase the accuracy of the spherical surface in the lens peripheral portion when designing the lens, which requires development costs. In addition, there are some lenses that cannot ensure accuracy during mass production, which may result in poor yield and high manufacturing costs.

(Object of invention)
An object of the present invention is to reduce the shift of the in-focus position due to the influence of various aberrations of the lens in the adjustment stage for adjusting the reference position of the zoom lens and the focus lens due to the dimensional tolerance in manufacturing the lens. An imaging device that can be used is provided.

  In order to achieve the above object, an imaging apparatus of the present invention limits a light beam incident through a zoom lens that performs zooming and a focus lens that performs focus adjustment and corrects a change in focal plane position due to the zooming. A diaphragm control unit for controlling the diaphragm unit, information on a relationship between the diaphragm control unit for limiting the opening amount of the diaphragm unit according to the position of the zoom lens and the subject distance between the zoom lens and the focus lens Storage means for storing focus position relationship information in a state where the opening amount of the aperture means is limited by the aperture control means, and the aperture according to the position of the zoom lens In a state where the opening amount of the means is limited, the focus position of the focus lens is detected, and the reference position of the zoom lens and the focus lens is adjusted. Is characterized in further comprising adjusting means that.

  According to the present invention, in the adjustment stage for adjusting the reference position of the zoom lens and the focus lens due to the dimensional tolerance in manufacturing the lens, it is possible to reduce the shift of the in-focus position due to the influence of various aberrations of the lens. it can.

1 is a block diagram illustrating a configuration of a video camera as an imaging apparatus that is Embodiment 1 of the present invention. FIG. 3 is a flowchart illustrating tele-middle tracking adjustment according to the first exemplary embodiment. 3 is a flowchart showing a continuation of FIG. 6 is a flowchart illustrating cam correction adjustment according to the first exemplary embodiment. 6 is a flowchart illustrating aperture focus correction control according to the first embodiment. It is a conceptual diagram which shows the change of the aperture amount to restrict | limit according to the focal distance in Example 1. FIG. FIG. 6 is a conceptual diagram illustrating an aperture focus correction amount according to an aperture amount according to the first exemplary embodiment. It is a flowchart which shows aperture focus correction | amendment control of Example 2 of this invention. FIG. 10 is a conceptual diagram illustrating an aperture focus correction amount according to an aperture amount according to the second exemplary embodiment. It is a conceptual diagram which shows the structure of a general rear focus type lens system. It is a conceptual diagram which shows the focusing cam locus | trajectory according to to-be-photographed object distance.

  The mode for carrying out the invention is as described in Examples 1 and 2 below.

  The feature of the first embodiment is that the reference position of the zoom lens and the focus lens caused by dimensional tolerances in manufacturing the lens in the actual lens is adjusted, and the deviation from the design data of the cam trajectory shape is designed. In the adjustment stage where adjustment is performed by matching with the locus, adjustment is performed by limiting the opening amount of the aperture to a state in which the aperture is reduced more than the aperture amount (F value) of the lens itself according to the focal length (zoom position). Thus, in detecting the actual in-focus position, it is intended to reduce the influence of the shift of the in-focus position due to the influence of various aberrations of the lens, particularly the spherical aberration. Further, in focus correction control when the aperture is changed, there is to suppress a variation remaining after correction due to variations in the mechanical opening position of the aperture.

  Embodiment 1 of the present invention will be described with reference to the drawings.

  FIG. 1 shows a configuration of a video camera as an image pickup apparatus equipped with a zoom lens, a focus lens, and a lens system including a diaphragm, which is Embodiment 1 of the present invention. Note that the present invention is not limited to a video camera, and can also be applied to various imaging devices such as a digital still camera.

  Reference numeral 101 denotes a fixed first lens group, reference numeral 102 denotes a zoom lens that is a second lens group that moves in the optical axis direction and performs zooming, and reference numeral 103 denotes an iris with a diaphragm blade structure that limits an incident light beam. A diaphragm 104 is a fixed third fixed lens group. Reference numeral 105 denotes a focus lens that is a fourth lens group that has a focus adjustment function and a compensator function that corrects a change in focal plane position due to zooming and moves in the optical axis direction behind the zoom lens 102. . The photographing optical system constituted by these lens group units is a rear focus optical system constituted by four lens groups having positive, negative, positive and positive optical powers in order from the object side (left side in the figure). . In the drawing, each lens group is described as being composed of a single lens. However, in actuality, it may be composed of a single lens or a plurality of lenses. It may be configured. In the first embodiment, a rear focus optical system will be described as an example. However, the present invention is not limited to this, and the present invention can be applied to an optical system having another lens configuration.

  Reference numeral 106 denotes an image sensor constituted by a CCD or CMOS sensor. The light beam from the object that has passed through the photographing optical system forms an image on the image sensor 106. The imaging element 106 photoelectrically converts the formed object image and outputs an imaging signal. The imaging signal is amplified to an optimum level by an amplifier (AGC) 107 and input to the camera signal processing circuit 108. The camera signal processing circuit 108 converts the input imaging signal into a standard television signal, which is sent to the monitor device 109 and displayed as a captured image.

  The output signal of the AGC 107 is also input to the AF signal processing circuit 114 and the AE detection circuit 115. The AF signal processing circuit 114 detects information corresponding to the contrast of the captured image. The AF evaluation value signal (sharpness signal) generated by the AF signal processing circuit 114 is read as data by communication with the camera microcomputer 116. The AE detection circuit 115 detects the luminance level from the output signal of the AGC 107, detects the exposure state of the subject, and outputs it to the aperture control means 117 in the camera microcomputer 116. The aperture control means 117 performs opening / closing control of the aperture 103 according to the output of the AE detection circuit 115.

  Reference numerals 110 and 111 denote a zoom drive source and a focus drive source such as a stepping motor for driving the zoom lens 102 and the focus lens 105 in the optical axis direction according to a drive signal output from a zoom / focus control means 119 described later. Reference numeral 112 denotes an aperture drive source such as an IG meter that drives the aperture 103 to open and close by a drive signal output from the aperture control means 117. Reference numeral 113 denotes a diaphragm amount detection means (iris encoder) using a Hall element or the like that detects the state of the diaphragm 103 (a diaphragm amount or an open amount).

  The camera microcomputer 116 includes an aperture control unit 117 that controls the aperture 103, and a frame generation unit 118 that generates a frame such as a so-called AF frame that limits the range of a captured image when generating the AF evaluation value signal described above. . In addition, a zoom / focus control unit 119 that outputs a signal for driving the zoom lens 102 and the focus lens 105 and controls the zoom lens 102 and the focus drive source 113 is provided. Furthermore, the cam locus storage means 120 for storing a plurality of electronic cam loci as information on the focus position relationship designed for each subject distance as shown in FIG. 11, the actual in-focus position at the time of adjustment and the cam locus storage means 120. A correction amount calculation unit 121 is provided that calculates a correction amount for correcting a shift by comparing with a stored design position.

  The zoom / focus control means 119 generates a signal (target drive position and drive speed) for driving the zoom lens 102 in the tele or wide direction corresponding to the direction in which an operation member such as a zoom switch (not shown) is operated. To do. Also, based on the AF evaluation value signal obtained from the AF signal processing circuit 114, a so-called AF operation is performed in which the focus lens 105 is driven in the closest or infinite direction via the focus drive source 111 to focus. The zoom / focus control unit 119 controls the focus lens 105 so as to correct the image plane movement accompanying the movement of the zoom lens 102 based on the cam track information stored in the cam track storage unit 120. Performs zoom (cam trace) operation.

  The diaphragm control unit 117 controls the diaphragm amount of the diaphragm 103 via the diaphragm drive source 112 in order to suppress the influence of the shift of the in-focus position and the decrease in the projection resolving power due to the influence of the aberration in the lens periphery. That is, data defining a limit value of the aperture opening amount according to the focal length (zoom position) as shown in FIG. 6 (the locus itself, a function using the lens position as a variable, or discrete table data may be used). Is compared with the current aperture amount output from the aperture amount detecting means 113. Then, the aperture amount of the aperture 103 is controlled so that they are the same. Here, management of the lens position referred to by the aperture control unit 117 will be described. In the first embodiment, the zoom drive source 110 and the focus drive source 111 are described as stepping motors, but the zoom / focus control means 119 has a stepping motor step counter. For example, a position of a reset sensor (not shown) is found when the camera is activated, and the position is grasped by increasing or decreasing the step counter according to the driving direction with reference to the step counter at that time. In addition, position detection means may be attached to the moving shafts of the respective lenses and position management may be performed based on the detection results.

  Next, a description will be given of an adjustment method and a post-adjustment focus correction control which are performed in the camera microcomputer 116 and adjust the shift for each lens manufactured product while reducing the influence of the lens aberration, which is a feature of the first embodiment.

  FIG. 2 is a flowchart showing the flow of tele-middle tracking adjustment in the first embodiment.

  In Step 201, the zoom lens 102 is moved to the zoom position Zs at the start of tele-middle tracking adjustment. In the first embodiment, the zoom position Zs is set to a zoom position corresponding to a position where the focus lens 105 reaches the highest point on the locus on the design cam locus. In Step 202, the aperture amount Is corresponding to the zoom position Zs is read out from the aperture amount (F value) data corresponding to the focal length (zoom position) as shown in FIG. In Step 203, it is determined whether or not the zoom lens 102 has reached the zoom position Zs set in Step 201, and whether or not the aperture is the aperture amount Is set in Step 202. If both of the conditions are satisfied, the process proceeds to Step 204. If neither of the conditions is satisfied, the process proceeds to Step 201. In Step 204, an AF focusing operation is performed in which the focus lens 105 is driven and focused based on the AF evaluation value calculated based on the video signal in the AF frame set by the frame generation means 118 in the AF signal processing circuit 114. And go to Step 205. Here, the subject distance is set to the adjustment distance, and a subject such as a chart for some adjustment is arranged.

  In Step 205, it is determined whether or not the subject is in focus, and the AF focusing operation in Step 204 is repeated until the subject is in focus. Actually, the focus position is searched while determining the moving direction in focus by examining the correlation between the AF evaluation value related to the contrast of the subject and the moving direction of the focus lens 105. Details are omitted in the flow.

  If it is determined in step 205 that the focus has been achieved, the focus lens position that is the focus position is stored as Fs in step 206, and the process proceeds to step 207. In Step 207, the focus lens 105 is moved to the infinite side by a specified amount A. Here, the defined amount A is defined by the distance from the position where the focus lens 105 is the highest point in the design cam trajectory shape to the focus lens focus position at the telephoto end. In Step 208, the zoom lens 102 is moved to a position Ztm slightly wider than the tele end at the design value. Here, the movement to the slightly wide position is caused by exceeding the in-focus position at the time when the search driving is started in the search of the in-focus zoom position by the search driving of the zoom lens 102 in Step 211 described later. This is to avoid being. If the in-focus position is exceeded, the driving direction of the zoom lens 102 is reversed and it takes time to search for the in-focus position, so that the in-focus position is not exceeded at the start time. However, when the control is performed by an actuator such as a stepping motor, the driving is reversed when the driving direction is reversed. Therefore, it is desirable to perform the search driving in the driving direction as a reference of the state where the backlash is shifted. In the first embodiment, the zoom search drive is described as being performed from the wide to the tele direction. However, in the case where the search drive is performed from the tele to the wide direction, in Step 208, the zoom lens 102 is slightly telescopic from the tele end at the design value. You may make it move to this position.

  In Step 209, the aperture amount It corresponding to the zoom position at the telephoto end is read and set. In Step 210, it is determined whether or not the zoom lens 102 has reached the zoom position Ztm set in Step 208, and whether or not the aperture amount is the aperture amount It set in Step 209. When both of the conditions are satisfied, the process proceeds to Step 211, and when neither of the conditions is satisfied, the process proceeds to Step 208. In Step 211, the zoom lens 102 is searched for a zoom position to be focused based on the AF evaluation value, and the focused zoom position is stored as Zt. This zoom position Zt corresponds to the zoom position at the tele end. In Step 212, the AF focusing operation is performed in the same manner as in Step 204, and the process proceeds to Step 213. In Step 213, similarly to Step 205, it is determined whether or not the subject is in focus, and the AF focusing operation in Step 213 is repeated until the subject is in focus.

  If it is determined in step 213 that the focus has been achieved, the focus lens position that is the focus position is stored as Ft in step 214 in FIG. 4, and the process proceeds to step 215. In Step 215, the focus lens 105 is moved to the close side by a specified amount A. In Step 216, the zoom lens 102 is moved from the zoom position Zt to the zoom position Zm that is moved to the wide side by a specified amount B. Here, the defined amount B is defined by the distance from the zoom position corresponding to the position where the focus lens 105 is the highest point in the design cam trajectory shape to the tele end position. In Step 217, the aperture amount Im corresponding to the zoom position Zm is read and set. In Step 218, it is determined whether or not the zoom lens 102 has reached the zoom position Zm set in Step 216, and whether or not the aperture amount is the aperture amount Im set in Step 217. If both of the conditions are satisfied, the process proceeds to Step 219. If neither of the conditions is satisfied, the process proceeds to Step 216. In Step 219 and Step 220, the AF focusing operation is repeated until focusing is performed in the same manner as in Step 204 and Step 205.

  If it is determined in step 220 that the focus is achieved, the focus lens position that is the focus position is stored as Fm in step 221, and the process proceeds to step 222. In Step 222, a difference between the focus lens position Fs stored in Step 206 and the focus lens position Fm stored in Step 221 is calculated, and it is determined whether or not the difference is within a specified value. Here, the specified value may be a value based on the depth of focus, or may be a value determined from an actual measurement value, and the adjustment accuracy improves when the value is as small as possible. If it is within the specified value, the process proceeds to Step 223, and if it is greater than the specified value, the process proceeds to Step 206 in FIG. 2, and the focus lens position at the time when Step 220 ends is overwritten as Fs. In Step 223, the tele end value and the wide end value, which are the reference positions of the zoom lens 102, are defined based on the zoom positions Zt and Zm. Further, the focus lens position Ft is determined as the reference position of the focus lens 105. In Step 224, the reference positions of the zoom lens 102 and the focus lens 105 determined in Step 223 are stored in a non-illustrated non-volatile memory (EEPROM) or the like.

  Next, after performing the tele-middle tracking adjustment described above, the amount of deviation between the actual in-focus position at the adjustment distance and the position on the designed cam locus at a plurality of zoom positions is detected and calculated as a correction amount. A cam correction adjustment method will be described. FIG. 4 is a flowchart showing the flow of cam correction adjustment in the first embodiment.

  In Step 301, the number n of zoom positions at which cam correction adjustment is performed is set. The zoom position for cam correction adjustment is set in advance in the table data or EEPROM. For example, the zoom stroke may be set to an equally divided zoom position, and the amount of deviation from the design cam locus and the deviation direction may vary. You may set the zoom position which becomes large. In the first embodiment, as shown in FIG. 6, description will be made on the assumption that cam correction adjustment is performed at seven points of a zoom position Z [n] (n = 6 to 0) including the tele end and the wide end. In Step 302, the zoom lens 102 is moved to the cam correction adjustment zoom position Z [n]. In Step 303, the focus lens position F [n] on the design cam trajectory at the zoom position value Z [n] set in Step 302 is read from the design cam trajectory information, and the focus lens 105 is moved to that position. In Step 304, the aperture amount I [n] corresponding to the zoom position Z [n] is read and set. Here, the aperture amount I [n] corresponding to the zoom position Z [n] is the aperture amount (F value) corresponding to the focal length (zoom position) as shown in FIG. 6 as in the tele-middle tracking adjustment. It is set based on data indicating the relationship (the locus itself, a function using the lens position as a variable, or discrete table data). In Step 305, whether or not the zoom lens 102 has reached the zoom position Z [n] set in Step 302, whether or not the focus lens 105 has reached the focus lens position F [n] set in Step 303, and the aperture amount. Is determined to be the aperture amount I [n] set in Step 304. When all the conditions are satisfied, the process proceeds to Step 306, and when any one is not satisfied, the process proceeds to Step 302.

  In Step 306, as in the tele-middle tracking adjustment, an AF focusing operation is performed based on the AF evaluation value, and the process proceeds to Step 307. In Step 307, it is determined whether or not the subject is in focus, and the AF focusing operation in Step 306 is repeated until the subject is in focus. If it is determined in step 307 that the focus has been achieved, the focus lens position that is the focus position is stored as F [n] ′ in step 308, and the process proceeds to step 309. In Step 309, the difference between the focus position F [n] set in Step 303 and the focus position F [n] ′ stored in Step 308 is calculated, and the difference is stored as a cam correction amount in a nonvolatile memory (EEPROM) or the like. . In Step 310, in order to move the zoom position to the next cam correction adjustment point, the index value n for referring to the zoom position is decremented, and the process proceeds to Step 311. In Step 311, it is determined whether or not the index value n for referring to the zoom position is smaller than 0. If it is equal to or larger than 0, the processing from Step 302 to Step 310 is repeated, and if it is smaller than 0, the cam correction adjustment is finished. finish.

  Next, focus correction, that is, so-called stop focus correction control when the focus position of the focus lens 105 is changed in accordance with the change in the stop amount of the stop 103 in the lens system that has been adjusted as described above will be described. FIG. 5 is a flowchart showing the flow of aperture focus correction control in the first embodiment.

  In Step 401, it is determined whether or not the MF is locked. If the MF is locked, the process proceeds to Step 402. If the MF is not locked (AF operation), the process is terminated without performing the aperture focus correction. With the MF lock function, the camera microcomputer 116 receives an input by a switch operation or menu operation (not shown) and fixes the focus lens position to the current position. In Step 402, the current zoom position Z and focus lens position F are detected. As described above, the reading of the zoom position and the focus lens position may be detected by the output of a position sensor (not shown), but in the first embodiment, it is read by the step counter of the stepping motor. In Step 403, the current aperture amount I is detected by an aperture amount detecting means (iris encoder) 113 using a Hall element or the like. In Step 404, an aperture amount threshold value Ith [n] for enabling aperture focus correction is set. Here, the setting of the aperture amount threshold value Ith [n] for enabling the aperture focus correction will be described. As described above, when the aperture is changed, the focus position changes due to the influence of aberration. However, for example, even when there is a change in the aperture amount and the in-focus position changes in a focused state with a certain predetermined aperture amount, if the change amount is small with respect to the depth of focus, it will not be seen as blurred. Therefore, there is no problem even if the aperture focus correction is not performed. Further, as the aperture is narrowed down, the depth of focus becomes deeper. Therefore, when the aperture is stopped from a certain predetermined aperture amount, even if there is a change in the in-focus position, it becomes invisible. Therefore, it is predicted by simulation or the like whether the amount of change in the in-focus position exceeds the depth of focus, and how much the aperture is limited from the amount of aperture that restricts the open amount at each zoom position (focal length). And if the amount of change in the focus position exceeds the depth of focus, you can correct the blur so that it will not be visible if you set the focus correction before changing to that amount. Can do. However, since the amount of change in the in-focus position differs depending on the aperture amount, it is not possible to perform proper correction simply by entering a correction amount uniformly. Therefore, a plurality of aperture amount threshold values for enabling the aperture focus correction may be set, and the correction amount to be corrected may be switched in accordance with the threshold values. In the first embodiment, description will be made assuming that the number of thresholds is 4 (n = 3 to 0).

  In Step 405, it is determined whether or not the aperture amount I detected in Step 403 is smaller than the threshold value Ith [n] set in Step 404. If it is reduced, the process proceeds to Step 406. If not, the process proceeds to Step 407. In Step 406, as shown in FIG. 7, the aperture focus correction amount Firis corresponding to the focal length (zoom position) is read. The aperture focus correction amount Firis is stored in a nonvolatile memory (EEPROM) (not shown). This memory corresponds to the correction amount storage means. Here, the aperture focus correction amount is set based on data indicating a correction amount corresponding to the focal length (zoom position) (the locus itself, a function using the lens position as a variable, or discrete table data). To do. FIG. 7 shows the focus position that changes when the aperture amount is set to I [2] and I [5] with respect to the focus position on the design cam trajectory in a state where the opening amount is limited as shown in FIG. A change amount, that is, a correction amount is shown. Since the amount of change is based on the focus position on the design cam trajectory with the opening amount limited, the influence of the variation in the focusing position due to the variation in the mechanical opening position as described above should be reduced. Can do. Since the opening amount is limited as shown in FIG. 6, for example, when the aperture amount is reduced to I [2], it is necessary to correct the telephoto area where the aperture amount exceeds I [2]. Therefore, the correction amount is set to zero. When the correction amount is stored in a discrete table, the correction accuracy can be increased by obtaining the correction amount by interpolation calculation according to the zoom position.

  In Step 407, it is determined whether or not the threshold index n is 0. If not, n is decremented in Step 408, and the processing from Step 404 to Step 405 is repeated. If n is determined to be 0 in Step 407, it is determined that the current aperture amount I is larger than any threshold value Ith [n], and the process ends without performing focus correction. In Step 409, the focus lens 105 is moved to a position obtained by adding the aperture focus correction amount Firis read in Step 406 to the current focus lens position F read in Step 402. In Step 410, it is determined whether or not the focus lens position (F + Firis) set in Step 409 has been reached, and Step 409 is repeated until the focus lens position is reached. The means for executing Step 409 and Step 410 corresponds to the focus correction control means.

  As described above, according to the first embodiment, the adjustment of adjusting the reference position of the zoom lens and the focus lens due to the dimensional tolerance in manufacturing the lens and adjusting the deviation from the design data of the cam locus shape. In aperture focus correction control when changing the stage or the aperture, it is possible to reduce the correction remaining due to the shift of the in-focus position due to the influence of various aberrations of the lens and the variation in the mechanical opening position of the aperture. Further, even when an inexpensive lens or a high magnification lens having lens aberration is used, zooming performance and focus correction performance can be ensured.

  In Example 1, the opening amount of the aperture is limited so that the influence of aberration is reduced, and aperture adjustment is performed when the lens is adjusted or the aperture is changed. However, when the amount of opening is limited, the aperture is narrowed down, so that the brightness of the subject cannot be sufficiently obtained particularly in the tele area, and it may be difficult to photograph a subject with low illuminance. Since the contrast of the subject is low at low illuminance, there is a risk of erroneous operation even in the AF focusing operation. In the case of low illuminance, there is a method of amplifying the image pickup signal by the AGC 107 to ensure brightness, but there is a disadvantage that the image quality is deteriorated because the noise included in the image pickup signal is also amplified. There are other methods of securing the brightness by slowing down the shutter speed. However, there are cases where the brightness cannot be secured even by combining them, and there is a case where it is desired to secure the light quantity by opening the aperture.

  Therefore, a feature of the second embodiment is that an appropriate aperture focus correction is performed in a lens system that controls the aperture to the open side even at the expense of resolution at low illuminance.

  The configuration of the second embodiment is the same as the configuration of the first embodiment. In the lens system that has been adjusted as described above, the brightness of the subject is dark, especially in the shooting at low illuminance, in order to ensure the brightness of the subject, more than the opening amount that restricts the aperture amount of the aperture 103. A description will now be given of aperture focus correction control for appropriately correcting the shift of the in-focus position due to a change in aperture amount even when the opening control is performed. FIG. 8 is a flowchart illustrating a flow of aperture focus correction control according to the second embodiment.

  In Step 701, it is determined whether or not the MF is locked. If the MF is locked, the process proceeds to Step 702. If the MF is not locked (AF operation), the process ends without performing the aperture focus correction. In Step 702, the current zoom position Z and focus lens position F are detected. In Step 703, the current aperture amount I is detected. In Step 704, the aperture amount I [Z] at the time of opening limit corresponding to the zoom position Z detected in Step 702 is read in the same manner as in the first embodiment. In Step 705, it is determined whether or not the aperture amount I detected in Step 703 is smaller than the aperture amount I [Z] read in Step 704. If the aperture is smaller than the aperture amount I [Z], the process proceeds to Step 706. Otherwise, the process proceeds to Step 713. This is a feature of the second embodiment. Whether the aperture amount is I [Z] when the opening amount is limited, that is, the aperture amount when adjusting (first correction mode), or is open (second). ) To switch aperture focus correction control. That is, the first correction mode and the second correction mode are switched according to the magnitude relationship between the aperture amount I and the aperture amount I [Z]. When the aperture is narrowed (first correction mode), the focus correction amount (first correction amount) when the aperture is narrowed in the same manner as in Step 404 to Step 408 of the first embodiment is read and opened (second correction mode). Reads out another correction amount (second correction amount). Steps 706 to 710 are the same as steps 404 to 408 of the first embodiment, except that the threshold value is replaced with Ith [n] by Iclose [n]. The explanation is omitted for simplicity. In Step 713, an aperture amount threshold value Iopen [n] for enabling the aperture focus correction is set. Here, the setting of the aperture amount threshold value Iopen [n] for enabling the aperture focus correction will be described. As in the case of narrowing down the aperture, set the aperture amount to enable aperture focus correction by predicting whether the change in focus position exceeds the depth of focus by simulation etc. It should be noted that because the depth of focus becomes shallower, it becomes easier to see as a blur. Similarly to the first embodiment, the amount of change in the in-focus position differs depending on the aperture amount. Therefore, it is not possible to perform appropriate correction simply by uniformly adding the correction amount. Therefore, the threshold value of the aperture amount that enables aperture focus correction is set. A plurality of values may be set and the correction amount to be corrected may be switched according to the threshold value.

  In Step 714, it is determined whether or not the aperture amount I detected in Step 703 is larger than the threshold value Iopen [n] set in Step 713. If it is open, the process proceeds to Step 715. If not, the process proceeds to Step 716. In Step 715, as shown in FIG. 8, the aperture focus correction amount Firis corresponding to the focal length (zoom position) is read out. FIG. 9 shows the amount of change in the focus position that changes when the aperture amount is set to I [2] with respect to the focus position on the design cam trajectory with the opening amount limited as shown in FIG. The correction amount is shown. It should be noted that the correction amount in the opening direction is set to 0 because it is not necessary to perform correction in the wide side region where the aperture amount is less than I [2] than the limited opening amount.

  In Step 716, it is determined whether or not the threshold index n is 0. If it is not 0, n is decremented in Step 717, and the processing from Step 713 to Step 714 is repeated. If it is determined in step 716 that n is 0, it is determined that the current aperture amount I is narrower than any threshold value Iopen [n], and the process ends without performing the focus correction. In Step 711, the focus lens 105 is moved to a position obtained by adding the focus correction amount Firis read in Step 708 or Step 715 to the current focus lens position F read in Step 702. In Step 712, it is determined whether or not the focus lens position (F + Firis) set in Step 711 has been reached, and Step 711 is repeated until the focus lens position is reached.

  As described above, according to the second embodiment, the adjustment of the lens is reduced by reducing the in-focus position shift due to the influence of various aberrations of the lens and the correction remaining due to the variation in the mechanical opening position of the diaphragm. It is possible to perform proper focus correction while ensuring the brightness of the subject at low illuminance, while performing focus correction when the aperture is changed.

  Although the present invention has been described in detail based on the preferred embodiments 1 and 2, the present invention is not limited to these specific embodiments, and various forms without departing from the gist of the present invention are also possible. It is included in the present invention. A part of the above-described embodiments may be appropriately combined.

DESCRIPTION OF SYMBOLS 102 Zoom lens 103 Aperture 105 Focus lens 113 Aperture amount detection means 116 Camera microcomputer 117 Aperture control means 119 Zoom / focus control means 120 Cam locus storage means 121 Correction amount calculation means

Claims (4)

A zoom lens that performs zooming, and a diaphragm control unit that controls a diaphragm unit that performs focus adjustment and restricts a light beam incident through a focus lens that corrects a change in a focal plane position accompanying the zooming, the zoom lens Diaphragm control means for limiting the opening amount of the diaphragm means according to the position of
Storage means for storing information on the relationship between the zoom lens and the focus lens for each subject distance, and information on the in-focus position in a state where the opening amount of the aperture means is limited by the aperture control means. Storage means for storing;
Adjusting means for detecting a focus position of the focus lens and adjusting a reference position of the zoom lens and the focus lens in a state where an opening amount of the aperture means is limited according to a position of the zoom lens; An imaging apparatus characterized by the above. A correction amount storage means for storing a correction amount for correcting a change in the focus position of the focus lens in accordance with a change in the aperture amount from the opening amount of the aperture means limited by the aperture control means;
A diaphragm amount detecting means for detecting a diaphragm amount of the diaphragm means;
The imaging apparatus according to claim 1, further comprising a focus correction control unit that corrects a position of the focus lens based on the aperture amount detected by the aperture amount detection unit and the correction amount.   3. The opening amount of the aperture means limited by the aperture control means is determined based on a projection resolving power of an image formed through the zoom lens and a focus lens. The imaging apparatus according to item 1. The focus correction control means includes a first correction mode for correcting the position of the focus lens by a first correction amount when the aperture is narrower than an opening amount of the restricted diaphragm means, and a restriction of the iris means to be restricted. A second correction mode for correcting by the second correction amount when the opening is larger than the opening amount;
Control is performed by switching between the first correction mode and the second correction mode in accordance with the magnitude relationship between the aperture amount detected by the aperture amount detecting unit and the limited opening amount of the aperture unit. The imaging apparatus according to claim 2.

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