KR100340943B1 - Zoom camera having a focusing error compensation and control method thereof - Google Patents

Abstract

The present invention discloses a zoom camera having a focus error correction function and a control method thereof. When the release switch is operated in the first stage of release, the final moving direction of the barrel is made in the opposite direction to the reference direction in which the gears are engaged during the zooming operation, and when the subject distance measured by the ranging means is far, Move the set distance further in the direction opposite to the direction set as the reference from the current remote zoom position, and then return to the remote zoom position to correct the focus error before taking a picture. On the other hand, if the measured subject distance is near, the barrel is moved to the near zoom position close to the far zoom position currently being positioned, and after the shooting, the barrel is moved back to the original far zoom position. As a result, a focus error due to a backlash or the like during the zoom operation is compensated for, and thus a picture having a precise focus can be taken regardless of the direction in which the zoom operation is performed.

Description

ZOOM CAMERA HAVING A FOCUSING ERROR COMPENSATION AND CONTROL METHOD THEREOF}

The present invention relates to a zoom camera having a focus error correction function and a control method thereof, and more particularly, to a zoom camera for correcting a focus error caused by a backlash amount of a zoom camera and a control method thereof.

In general, a zooming method of a zoom camera is to move a lens barrel in a corresponding direction as a user moves a zoom switch mounted on the camera to a wide or wide tele.

When the user selects tele or wide operation by operating the zoom switch, the control unit drives the barrel driving integrated circuit (IC), and the barrel driving IC rotates the motor in the corresponding direction, thereby moving the lens barrel to the set position. .

At this time, the control device determines whether the barrel has been moved to the corresponding position according to an encoder outputted from an encoder whose contact point is variable in connection with the barrel, that is, a sensor for detecting the zoom position of the lens barrel. The zoom operation ends when the position is reached.

However, when moving the barrel from the wide to the tele and from the tele to the wide, the focus error occurs due to the backlash of the gears, which are mechanical parts, and the difference between the boundary and the boundary distance of the encoder.

More specifically, in the case where the position and the direction in which the gears for moving the barrel are engaged based on the movement of the barrel from the wide to the tele in the zooming operation are designed, the gear is moved from the tele to the wide. The position and direction of engagement are changed so that the barrel is not positioned in the correct position.

In the zoom camera, since the AF step according to the subject distance is set based on the position where the barrel stops due to the gears that move the barrel along the camera design reference direction, the barrel is moved from tele to wide as described above. In the case of moving, the focus is not achieved even if the focus is adjusted according to the subject distance.

Therefore, an object of the present invention is to provide a zoom camera that compensates for a focus error caused by backlash.

1 is a block diagram of a zoom camera having a focus error correction function according to an embodiment of the present invention.

2A is a structural diagram of a barrel position detecting unit according to an embodiment of the present invention.

2B is a waveform diagram of a signal of a barrel position detector according to an embodiment of the present invention.

3 is a state diagram illustrating a barrel movement operation of a zoom camera according to an embodiment of the present invention.

4 is an operation flowchart of a focus adjustment method in the zoom operation from the wide to the tele direction according to the embodiment of the present invention.

5 is a flowchart illustrating a method of adjusting a focus during tele to wide zooming according to an embodiment of the present invention.

In order to achieve the above object, a zoom camera having a focus error correction function according to a feature of the present invention has one of a first direction in which a barrel moves from a wide to a tele direction and a second direction in which a barrel moves from a tele to a wide direction. The zoom camera is designed to be geared to move the barrel on the basis of the reference, and the barrel is selectively moved to a plurality of remote zoom positions set on the basis of a long distance, a plurality of short zoom positions set on the basis of a short distance. in,

A zoom switch for selecting a zoom operation for moving the barrel from the wide direction to the tele direction or for moving the barrel from the tele direction to the wide direction; Barrel moving means for moving to a corresponding remote zoom position during a zoom operation; Barrel position detecting means for detecting a far zoom position and a near zoom position respectively according to the movement of the barrel; Ranging means for measuring a subject distance; A release switch which is sequentially operated in the first and second release stages when the photographing operation is selected; And when the release switch is operated in the first stage of release, the final moving direction of the barrel is made in a direction opposite to the direction set as the reference, and when the subject distance measured by the ranging means is far, the barrel is currently far The barrel moving means is driven to move further a set distance in a direction opposite to the direction set as a reference from the zoom position and then returns to the remote zoom position, and when the subject distance measured by the ranging means is near, the barrel is A control means for driving the barrel moving means to move to the near zoom position close to the currently located far zoom position to perform a focus error correction operation, and then output a photographing signal; And photographing means for photographing by operating the shutter according to the photographing signal.

On the other hand, when the subject distance measured by the ranging means is close, the barrel is positioned at the near zoom position and photographed, and then the barrel is moved back to the original far zoom position.

The barrel position detecting means includes: a pattern portion comprising a far-field pattern indicating a plurality of far-field zoom positions according to a zooming operation and a near-field pattern indicating a plurality of near-field zoom positions; And a pattern detecting unit for detecting a far zoom position according to the far pattern in conjunction with the barrel movement, detecting a near zoom position according to the near pattern, and outputting a corresponding electric signal to the control means.

According to another aspect of the present invention, a control method of a zoom camera having a focus error correction function includes a first direction in which a barrel moves from a wide to a tele direction and a second direction in which a barrel moves from a tele to a wide direction. In a zoom camera that is designed to be engaged with the gears to move the barrel on the basis of the reference, the barrel is selectively moved to a plurality of remote zoom position set on the basis of the remote, a plurality of near zoom position set on the basis of the short range Selectively moving the barrel in a first direction or a second direction according to the zoom switch operation; Determining whether the release switch for starting photographing when the zooming operation is completed; Measuring a subject distance when the release switch is operated in a first release stage; When the final movement direction of the barrel is made in the direction opposite to the direction set as the reference and the measured object distance is far, the barrel is further moved in the direction opposite to the direction set as the reference at the current far zoom position, and then Performing focus error correction by returning to the far zoom position; When the final moving direction of the barrel is made in the direction opposite to the direction set as the reference and the measured object distance is near, the barrel is moved to a near zoom position close to the far zoom position at which the current position is positioned to perform focus error correction. Doing; And photographing after performing the focus error correction.

In the photographing step, when the subject distance is close, it is preferable to return the barrel back to the original far zoom position.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 shows a structure of a zoom camera having a focus error correction function according to an embodiment of the present invention, FIG. 2A shows a structure of a barrel position detecting unit according to an embodiment of the present invention, and FIG. 2B illustrates the present invention. The signal waveform of the barrel position detector according to the embodiment of the present invention is shown.

As shown in FIG. 1, a zoom camera having a focus error correction function according to an exemplary embodiment of the present invention includes a distance measuring unit 10, a light metering unit 20, a barrel position detecting unit 30, a main switch SW1, and a zoom camera. A release switch SW2, a tele switch SW31 and a wide switch SW32 for a zoom operation, a control unit 40 connected to an output end thereof, and a barrel moving unit connected to an output end of the control unit 40; 50, the display unit 60, and the shutter unit 70.

The ranger 10 measures the distance between the camera and the subject, and the photometer 20 measures the luminance of the subject. Metering unit 10 and the light metering unit 20 is a known technique, so a detailed description thereof will be omitted.

As shown in FIG. 2, the barrel position detecting unit 30 includes a pattern portion 31 including a ground pattern 311, a distant pattern 313, a close pattern 315, and a near field pattern 317. It is provided and is in contact with each pattern of the pattern portion 31 in accordance with the movement of the barrel consists of a pattern detecting unit 33 for outputting an electrical close signal (A), a long distance signal (B), a short-range signal (C), respectively.

The close pattern 315 is a pattern indicating a close position where the barrel is stored in the camera. The distant pattern 313 represents angular focus positions for focusing when the object distance is farther than the reference distance (for example, 3.2 m), and the pattern is used for zooming in the tele direction or the wide direction at the same time. Indicates the zoom position. The short distance pattern 317 is a pattern representing respective focal positions for focus adjustment when the object distance is closer than the reference distance, and each pattern 311, 313, 315, and 317 is made of a conductor. As shown in FIG. 2, the far-field pattern 313 and the near-field pattern 317 are formed at a predetermined interval so that the conductor pattern is detected at each focal position.

The barrel moving unit 50 is composed of a motor M and a plurality of gears for transmitting power to the barrel in association with the motor M, and detailed structures thereof are well known and thus will be omitted.

The pattern detecting unit 33 is composed of a brush installed in one of the plurality of gears, one terminal of the brush is in contact with the ground pattern 311, and the other terminal is a long-distance pattern 313 by moving the barrel in the optical axis direction. ) And the close pattern 315 and the near pattern 317 may be selectively contacted with each other.

Therefore, when the gear rotates according to the driving of the motor M, the pattern detecting unit is configured as the other terminal selectively contacts each pattern 313, 315, and 317 while one terminal of the brush is in contact with the ground pattern 311. 33 outputs a low level or high level signal. For example, in the embodiment of the present invention, when the brush, which is the pattern detecting unit 33, contacts each of the patterns 313, 315, and 317, a corresponding signal having a low level is output, and the respective patterns 313, 315, and 317 are output. If it does not touch), the corresponding signal of high level is output.

Signal configuration for each zoom position of the barrel position detecting unit 30 according to the embodiment of the present invention is as follows.

division One Close One 0 0 0 2 Gap1 One One 0 0 3 38 mm (round) One 0 One One 4 Gap2 One One One One 5 38 mm (root) One 0 One 0 6 Gap2 One One One One 7 45 mm (round) One One 0 One 8 Gap2 One One One One 9 45 mm (root) One One One 0 10 Gap2 One One One One 11 50 mm (round) One 0 0 One 12 Gap2 One One One One 13 50 mm (root) 0 One 0 0 14 Gap2 One One One One 15 60 mm (round) 0 One 0 One 16 Gap2 One One One One 17 60 mm (root) 0 One One 0 18 Gap2 One One One One 19 70 mm (round) 0 One One One 20 Gap2 One One One One 21 70 mm (root) 0 0 One 0

The control unit 40 controls zooming from wide to tele and tele to wide according to the remote pattern 311 of the barrel position detecting unit 30 when the tele switch SW31 or the wide switch SW32, which is a zoom switch, is operated. When the zooming control unit 41 and the release switch SW2 are operated to control the zoom operation of the camera, it is determined whether the object distance measured by the distance measuring unit 10 is far or near, and then the far pattern 313 or the near pattern. According to 317, the AF control unit 43 controls the focus adjustment operation at a long distance or near distance, and the exposure control unit 45 controlling the exposure amount according to the object distance and luminance.

The zooming control unit 41 outputs a tele signal or a wide signal for controlling the zooming operation, and the barrel moving unit 50 rotates the motor M forward according to the tele signal and reverses the motor M according to the wide signal. Rotate The AF controller 43 outputs a focus adjustment signal for controlling the AF operation, and the barrel movement unit 50 rotates the motor M forward according to the focus adjustment signal.

Under the control of the exposure controller 45, the shutter unit 70 captures light corresponding to a subject to the film through the photographing lens.

The main switch SW1 is a switch for supplying power to each device of the camera to set the camera to a shooting standby state. The release switch SW2 is a switch for initiating a photographing operation. When the user presses a shutter button (not shown) to start photographing, the release switch SW2 is sequentially operated to release first stage and release second stage in association with the shutter button. The zoom switch is composed of a tele switch SW31 for moving the barrel in the tele direction and a wide switch SW32 for moving the barrel in the wide direction.

The operation of the zoom camera having the focus error correction function according to the embodiment of the present invention having such a structure will be described.

The zoom camera described below is a zoom camera designed to be engaged with gears for moving the barrel on the basis of the barrel moving in the wide to tele direction, but is not limited thereto.

3 illustrates a barrel movement operation of a zoom camera according to an embodiment of the present invention, and FIG. 4 illustrates an operation flowchart of a focus adjustment method during a zoom operation in a wide to tele direction according to an embodiment of the present invention. FIG. 5 shows an operation flowchart of a focus adjustment method in the tele to wide zoom operation.

First, the focus adjustment operation during the zoom operation from the wide to the tele direction will be described. As shown in FIG. 4, when the user operates the main switch SW1 of the camera to take a picture, a power supply of a battery unit (not shown) is applied to each device (photometer, ranger, etc.), and the zooming control unit ( 41 drives the barrel moving part 50 to move the barrel from the closed position to the open position.

When the main switch SW1 is not operated in the automatic zoom camera, the barrel is positioned at a closed position accommodated inside the camera, and when the main switch SW1 is operated, the barrel is moved to an open position that can be photographed. In general, since the lens cover is closed in the closed position, photographing is not performed. As the lens cover is opened as the lens cover is moved to the open position, the photographing is possible.

As the barrel moving unit 50 rotates the motor M forward, the barrel starts to move out of the camera at a close position stored in the camera, and at this time, the pattern detecting unit is interlocked with the barrel moving unit 50. As shown in FIG. 2, when 33 detects the close pattern 315 and outputs the low level close signal A, when the barrel starts to move, the high level close signal A is output. .

When the high level close signal A is output from the barrel position detector 30, the zooming controller 41 determines that the barrel is being moved to the open position, and continues to the barrel mover 50 until the open position is detected. ).

When the barrel continues to move toward the open position and the pattern detecting unit 33 detects the open position (f = 38mm in FIG. 3) of the far pattern 313, the pattern detecting unit 33 generates a low level far signal B. Outputs When the low-distance long distance signal B is output from the barrel position detector 30, the zoom controller 41 determines that the barrel is moved to the open position and stops the motor (S110 to 120).

After stopping the barrel movement in the open position as described above, the zooming control unit 41 determines whether to select the zoom operation. When the tele switch SW31 for moving the barrel in the tele direction is operated, the zooming control unit 41 outputs a tele signal, and the barrel moving unit 50 rotates the motor M forward in response to the tele signal. Start to move in the tele direction (S130).

As the barrel is moved in the tele direction, the pattern detector 33 of the barrel position detector 30 also starts to move in the tele direction, whereby the pattern detector 33 is a low-distance long distance signal B in the open position. While outputting the signal, the high-distance long distance signal B is started to be output as the barrel moves.

When the tele switch SW31 is turned off while the barrel is being moved in this manner, the zooming controller 41 causes the far-field signal B output from the barrel position detector 30 to move from a high level to a low level according to the remote feeding position detection. If converted, the operation of the barrel moving unit 50 is stopped.

Therefore, when the tele switch SW31 is operated in the open position (f = 38mm) as shown in FIG. 3, the barrel moves according to the rotation of the motor M. At this time, when the tele switch SW31 is turned off, the barrel is turned off. It stops at the remote feeding position (f = 45mm) (S140).

That is, according to the operation of the tele switch SW31, the barrel is continuously moved in the tele direction, and when the tele switch SW31 is turned off, the barrel is stopped at the remote feeding position.

Next, when the tele switch SW31 is operated again, the zooming control unit 41 rotates the motor M forward as described above so that the barrel is positioned at the next remote feeding position (for example, f = 60mm) (S150). ).

As described above, when the barrel performs the zoom operation in the tele direction, and the user operates the release switch SW2 to start shooting, the AF control unit 43 performs the shooting operation (S160).

When the first stage of the release switch SW2 is operated, the AF controller 43 operates the ranger 10 and the photometer 20 to measure the subject distance and the brightness of the subject. The exposure amount and the exposure time are calculated according to the luminance (S170 to S180).

The AF control unit 43 compares the measured subject distance with a set reference distance (for example, 38 mm), determines that the measured subject distance is shorter than the reference distance, and determines that the measured subject distance is short distance if the subject distance is larger than the reference distance. It is determined (S190).

Next, when the release switch SW2 is operated in the second release stage, the AF control unit 43 performs AF adjustment depending on whether the measured object distance is near or far.

More specifically, since the zooming operation is performed based on the long distance pattern 313, when the subject distance is near, the AF control unit 4 outputs a focus adjustment signal for forward rotation of the barrel moving unit 50. According to the focus adjustment signal, the barrel moving unit 50 rotates the motor M forward to move the barrel in the tele direction from the corresponding zoom position, that is, the remote feeding position. As the barrel is moved, the pattern detector 33 detects the near pattern 317 close to the far pattern 313 and outputs a corresponding pulse signal, and the AF controller 43 receives the near pattern from the barrel movement detector 30. The AF operation is stopped at the time point at which the signal according to the detection is output (S200 to S210).

For example, as shown in FIG. 4, when the barrel is located near the second remote dispensing position (f = 45 mm) according to the zooming operation, and the object distance is determined to be near, the barrel is rotated forward to the second remote dispensing position. To the second near-feed position for focus control

When the above-described AF operation is completed, the exposure controller 45 drives the shutter unit 70 to open the shutter by the exposure amount for the calculated exposure time (S220). When the shutter operation is completed, that is, when the photographing is finished, the AF control unit 43 returns the barrel to the remote feeding position set in accordance with the zooming operation. That is, the barrel is reversely rotated to move from the second near-immediate dispensing position positioned in accordance with the AF operation to the second remote dispensing position (S230).

On the other hand, when the release switch SW2 is operated in the second release stage when the subject distance is far, the AF controller 43 does not perform a separate AF operation because the zoom operation is performed based on the far pattern 313. In addition, the exposure controller 45 performs shooting by operating the shutter as described above at the current barrel position (S240 to S250).

For example, when the barrel is positioned at the second remote dispensing position (f = 45mm) according to the zooming operation, imaging is performed at the second remote dispensing position. Even after the shooting is completed, the barrel continues to be positioned at the second remote dispensing position.

Next, a focus adjustment operation in the case of performing a zoom operation in the tele direction in the tele will be described.

As shown in FIG. 5, when the wide switch SW32 is operated, the zooming control unit 41 outputs a wide signal to the barrel moving unit 50, and the barrel moving unit 50 is connected to the motor M according to the wide signal. Reverse rotation to move the barrel in the wide direction.

For example, when the wide switch SW32 is operated while the barrel is positioned at the tele position, that is, the fourth remote dispensing position (f = 70 mm) as shown in FIG. 3, the zooming controller 41 is configured to move the barrel. By controlling 50, the barrel is moved to the next remote dispensing position, that is, the third remote dispensing position (f = 60mm). In this case as well, the zooming control unit 41 determines the movement state of the barrel in accordance with the level change of the far-field signal A output from the barrel position detecting unit 30 in the same way as the zooming operation in the tele direction. It moves to the feeding position (S310-S320).

In this state, when the wide switch SW32 is operated again, the zooming control unit 41 repeatedly performs the above-described operation to continuously move the barrel in the wide direction (S330).

When the release switch SW2 is operated in the first release stage after the zoom operation in the wide direction is performed in this manner, the AF control unit 43 operates the ranger 10 and the light metering unit 20, respectively, The luminance of the subject is measured, and an exposure amount and an exposure time are calculated (S350 to S360).

Next, it is determined whether the measured distance is close or near by comparing the measured distance with the reference distance (S370). When the release switch SW2 is operated in the release 2 stage when the close distance is close, the zoom in the tele direction described above is performed. In the same manner as the operation, the AF control unit 43 moves the barrel to the near-field dispensing position for focusing at the current far-field dispensing position to perform shooting, and then returns the barrel to the original far-field dispensing position (S380 to S410). ).

On the other hand, when the release switch SW2 is operated in the second release stage when the object distance is far, the AF controller 43 performs a focus adjustment operation to compensate for the focus error caused by the backlash.

More specifically, since the zoom camera according to the embodiment of the present invention is designed to be engaged with gears for moving the barrel on the basis of the barrel moving from the wide to the tele direction, the tele-wide as described above. When the zooming operation is performed, the positions where the gears are engaged are changed.

In order to correct the change in the position at which these gears are engaged, that is, to correct the amount of backlash, the control section 43, for example, as shown in the accompanying FIG. 4, the subject distance in the state that the barrel is located at the third remote feeding position. If is determined to be far, the barrel moving unit (M) is controlled so that the barrel is moved a predetermined distance in the wide direction to return to the original third remote feeding position (S430).

As the barrel moving unit 50 rotates the motor M in a reverse direction to move the barrel in the wide direction from the third remote dispensing position, the barrel position detecting unit 30 outputs a low level remote signal B and then high. The long distance signal B of the level is output. The AF control unit 43 causes the motor M to rotate in the reverse direction for a predetermined time when the high-distance remote signal B is output, and then rotates the motor M forward again when the set time elapses, thereby returning the barrel to the original. Move to the third remote dispensing position. Accordingly, when a low level signal is output from the barrel position detector 30, the AF controller 43 stops driving the barrel mover 50 to stop the motor M.

Therefore, the barrel is positioned at the third remote feeding position while the focus error caused by the backlash is corrected.

As described above, after performing the focus adjustment during the zoom operation in the wide direction, the exposure controller 45 operates the shutter unit 60 according to the calculated exposure amount to perform photographing (S440).

In the above-described embodiment, the motor M is stopped when the corresponding remote dispensing position or the near dispensing position is detected. Alternatively, when the short-range signal C is output, the barrel may be further moved in the moving direction for a predetermined time and the motor M may be stopped.

In addition, although the zoom operation is performed based on the far pattern 313 in the embodiment of the present invention, the present invention is not limited thereto, and the far distance pattern 313 is performed when the subject distance is far while performing the zoom operation based on the near pattern 317. It is also possible to make focus adjustment on the basis of.

In the exemplary embodiment of the present invention, the functions of the control unit 40 are divided into the zooming control unit 41, the AF control unit 43, and the exposure control unit 45 for convenience, but the present invention is not limited thereto. And control the shooting operation.

This invention is capable of various modifications and implementations without departing from the scope of the following claims.

As described above, according to the embodiment of the present invention, it is possible to always take a picture with the correct focus regardless of the direction in which the barrel moves.

Claims (5)

The gear is designed to be engaged with the gears for moving the barrel relative to one of a first direction in which the barrel moves from the wide to the tele direction and a second direction in which the barrel moves from the tele to the wide direction. In a zoom camera that is selectively moved to a plurality of far zoom positions set on the basis of a plurality of short distance zoom positions set on the basis of a short distance, A zoom switch for selecting a zoom operation for moving the barrel from the wide direction to the tele direction or for moving the barrel from the tele direction to the wide direction; Barrel moving means for moving to a corresponding remote zoom position during a zoom operation; Barrel position detecting means for detecting a far zoom position and a near zoom position respectively according to the movement of the barrel; Ranging means for measuring a subject distance; A release switch which is sequentially operated in the first and second release stages when the photographing operation is selected; And When the release switch is operated in the first stage of release, the final movement direction of the barrel is made in the opposite direction to the direction set as the reference, and when the object distance measured by the ranging means is far, the barrel is currently zoomed far. Driving the barrel moving means to further move a set distance in a direction opposite to the direction set as a reference from the position and then return to the far zoom position, If the subject distance measured by the ranging means is close, the barrel moving means is driven to move the barrel to a near zoom position close to the far zoom position at which the current position is located, and then a focus error correction operation is performed. Control means for outputting; Shooting means for shooting by operating the shutter according to the shooting signal Zoom camera having a focus error correction function comprising a. The method of claim 1 wherein the control means If the subject distance measured by the measuring means is a short distance, a focus error of driving the barrel moving means to move the barrel back to the original far zoom position after photographing the barrel at a near zoom position. Zoom camera with correction function. The method of claim 1, The barrel position detecting means, A pattern unit including a far field pattern indicating a plurality of far zoom positions and a near pattern indicating a plurality of near zoom positions according to a zooming operation; And The pattern detecting unit detects a far zoom position according to the far pattern in conjunction with the barrel movement, detects a near zoom position according to the near pattern, and outputs a corresponding electrical signal to the control means. Zoom camera having a focus error correction function comprising a. The gear is designed to be engaged with the gears for moving the barrel relative to one of a first direction in which the barrel moves from the wide to the tele direction and a second direction in which the barrel moves from the tele to the wide direction. In a zoom camera that is selectively moved to a plurality of far zoom positions set on the basis of a plurality of short distance zoom positions set on the basis of a short distance, Selectively moving the barrel in the first direction or the second direction according to the zoom switch operation; Determining whether the release switch for starting photographing when the zooming operation is completed; Measuring a subject distance when the release switch is operated in a first release stage; When the final movement direction of the barrel is made in the direction opposite to the direction set as the reference and the measured object distance is far, the barrel is further moved in the direction opposite to the direction set as the reference at the current far zoom position, and then Performing focus error correction by returning to the far zoom position; When the final moving direction of the barrel is made in the direction opposite to the direction set as the reference and the measured object distance is near, the barrel is moved to a near zoom position close to the far zoom position at which the current position is positioned to perform focus error correction. Step; and Photographing after performing the focus error correction Control method of a zoom camera having a focus error correction function comprising a. The method of claim 4, wherein And a focus error correction function for returning the barrel back to the original far zoom position when the subject distance is close at the photographing step.