KR101712545B1 - Apparatus and method for de-focusing of infrared detector - Google Patents

Abstract

The present invention relates to a defocus device and a defocus method of an infrared ray detector, and more particularly, to a defocus device and a defocus method of an infrared ray detector for adjusting the focus of an infrared ray detector so as to have a uniform sensitivity in all pixels .
The defocus device of an infrared detector according to an embodiment of the present invention includes a lens unit including a first lens unit and a second lens unit and adjusting a magnification according to an interval between the first lens unit and the second lens unit; A memory unit for storing a focus setting position and a defocus setting position according to the magnification of the lens unit, respectively; An error measuring unit for respectively calculating an actual focus position according to a magnification of the lens unit and calculating focus offset values corresponding to a difference between the focus setting position and the actual focus position; A control unit for determining a defocus correction position from the defocus setting position and the focus offset values; And a driving unit for moving the first lens group and the second lens group to the defocus correction position, respectively.

Description

TECHNICAL FIELD [0001] The present invention relates to a defocus device and a defocus method for an infrared ray detector,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defocusing apparatus and a defocusing method for an infrared ray detector, and more particularly to a defocusing apparatus and a defocusing method of an infrared ray detector for adjusting a focus of an infrared ray detector will be.

A key component of thermal imagers that detect the difference between the radiant energy emitted by the target and the background in the absence of light is the infrared detector.

The operating principle of the infrared detector is to detect the infrared rays of the infrared region of the infrared ray emitted from the object (the long wave region has a wavelength of 8 to 12 μm and the middle wave region has a wavelength of 3 to 5 μm). The electric signal converted through the infrared ray detector is displayed on the monitor and displayed as a constant image according to the temperature distribution of the object. Infrared detectors are variously classified according to the wavelength band and the cooling method.

In the case of an infrared detector, fixed pattern noise (FPN) is generated in the horizontal and vertical directions due to the processing in row and column units. In order to suppress such fixed pattern noise, Non-uniformity correction (NUC) processing is indispensable for uncooled infrared detectors.

This nonuniformity correction processing is performed by using a nonuniform correction table which is calculated with a uniform sensitivity in all the pixels. Here, in order to create a non-uniformity correction table that is calculated with a uniform sensitivity in all pixels, it is necessary to capture a uniform surface having a uniform temperature to obtain output data of a uniform surface.

Conventionally, in order to form such a uniform surface, a separate defocus optical system is added to the lens portion of the thermal imaging camera or the inner surface of the shutter for opening and closing the lens is used as a uniform surface. However, when a separate defocus optical system is added to the lens unit or a shutter for opening and closing the lens is used, there arises a problem of space limitation and cost increase of the thermal imaging camera by additional additional equipment. In addition, even when the lens portion of the thermal imaging camera is defocused to form a uniform surface, the actual focus position can be determined visually, whereas the actual defocus position can not be distinguished by the naked eye, There is a problem that it is difficult to do.

KR 10-1076027 B1

The present invention provides a defocusing apparatus and a defocusing method of an infrared ray detector capable of aligning a lens unit of an infrared ray detector to an efficient defocus position in order to correct non-uniformity of an infrared ray detector.

The defocus device of an infrared detector according to an embodiment of the present invention includes a lens unit including a first lens unit and a second lens unit and adjusting a magnification according to an interval between the first lens unit and the second lens unit; A memory unit for storing a focus setting position and a defocus setting position according to the magnification of the lens unit, respectively; An error measuring unit for respectively calculating an actual focus position according to a magnification of the lens unit and calculating focus offset values corresponding to a difference between the focus setting position and the actual focus position; A control unit for determining a defocus correction position from the defocus setting position and the focus offset values; And a driving unit for moving the first lens group and the second lens group to the defocus correction position, respectively.

Wherein the control unit selects one of the focus offset values according to magnifications of the first lens group and the second lens group and adds the selected focus offset value to the defocus setting position stored in the memory unit, The position can be determined.

The controller may compare the sensitivities according to magnifications of the first lens group and the second lens group to select a focus offset value for each lens group.

Wherein the error measuring unit determines a temperature correction position corresponding to a temperature change of the lens unit and calculates a temperature offset value corresponding to a difference between the actual focus position and the temperature correction position, It is possible to determine the defocus correction position.

According to another aspect of the present invention, there is provided a defocus method for an infrared ray detector, comprising: storing a focus setting position and a defocus setting position according to a magnification of a lens unit including a first lens group and a second lens group; Determining an actual focus position according to a magnification of the lens unit; Calculating focus offset values corresponding to a difference between the actual focus position and the focus setting position; Determining a defocus correction position from the defocus setting position and the focus offset values; And moving the first lens group and the second lens group to the defocus correction position, respectively.

Wherein the step of determining the defocus correction position comprises the steps of: comparing sensitivity of each of the first lens group and the second lens group according to a magnification; Selecting a focus offset value having the highest sensitivity among the focus offset values of the first lens group and the second lens group; And determining a defocus correction position by adding the selected focus offset value to a defocus setting position of each of the first lens group and the second lens group.

The process of calculating the focus offset values may be performed while maintaining a constant temperature.

Determining a temperature correction position according to a temperature change of the lens unit; And calculating a temperature offset value corresponding to a difference between the actual focus position and the temperature correction position, wherein the step of determining the defocus correction position further comprises: The focus correction position can be determined.

Wherein the step of determining the temperature correction position and the step of calculating a temperature offset value are repeated by varying the temperature of the lens unit at a constant temperature interval and the step of determining the defocus correction position comprises: It is possible to determine the defocus correction position by reflecting the temperature offset value corresponding to the current temperature of the lens unit among the temperature offset values.

According to the defocus device and the defocus method of the infrared ray detector according to the embodiment of the present invention, the focus offset value corresponding to the difference between the actual focus position and the focus setting position is applied to the defocus setting position, An accurate defocus correction position reflecting the error can be determined.

Further, not only the optical error and the mechanical error according to the shape and the interval of the lens but also the focus change according to the temperature change caused by the contraction or expansion of the lens due to the change of the ambient temperature are reflected in the defocus correction position, It can be defocused to have a uniform sensitivity in all the pixels.

In addition, the non-uniformity correction table can be created by correct defocus correction position, and the non-uniformity of the thermal imaging camera can be more accurately corrected by the non-uniformity correction table, thereby providing a stable thermal image without noise.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing a defocusing apparatus of an infrared ray detector according to an embodiment of the present invention; Fig.
Fig. 2 is a view exemplarily showing focus offset values of the first lens group and the second lens group at a low magnification. Fig.
3 is a view exemplarily showing focus offset values of the first lens group and the second lens group at a high magnification.
4 is a view exemplarily showing a state in which defocus correction positions of the first lens group and the second lens group are determined;
5 is a flow chart schematically illustrating a defocusing method of an infrared detector according to an embodiment of the present invention.

The defocus device of the infrared ray detector according to the present invention and the non-uniformity correction method using the same are technically capable of aligning the lens portion of the infrared ray detector with a correct defocus position so as to form a uniform surface having a uniform temperature in order to correct the non-uniformity of the infrared ray detector. It presents features.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, Is provided to fully inform the user. Wherein like reference numerals refer to like elements throughout.

Prior to the description of the present invention, an example of obtaining a thermal image in an infrared detector will be briefly described.

The infrared detector detects an infrared ray of an object (subject) and converts it into an electrical signal. The principle of operation of the infrared ray detector is a wavelength range of the infrared ray region (8 to 12 μm long wave range, (Hereinafter, referred to as " thermal image data ") is obtained on a frame-by-frame basis.

As described above, the infrared ray detector detects infrared rays of a subject to obtain thermal image data in the form of an electrical signal, and the obtained thermal image data is digitized by a predetermined amount of bits. At this time, the thermal image data obtained from the subject of the same target does not have a constant value but has a constant value according to the temperature of the infrared ray detector.

Since the infrared detector can not maintain the constant temperature, the temperature of the infrared detector changes as the external temperature changes. Therefore, the thermal image data, which is the output value of the thermal image for the same target, does not appear constantly. Fixed pattern noise (FPN: Fixed Pattern Noise) occurs when image processing is completed by using thermal image data, which is an output value of a thermal image, but has a value that varies with temperature without being constant.

In order to remove such fixed pattern noise, the infrared detector is subjected to a nonuniformity correction (NUC) process for correcting non-uniformity using a non-uniformity correction table calculated with uniform sensitivity at all pixels. Here, in order to create a non-uniformity correction table that is calculated with a uniform sensitivity in all pixels, it is necessary to capture a uniform surface having a uniform temperature to obtain output data of a uniform surface.

Conventionally, in order to form such a uniform surface, a separate defocus optical system is added to the lens portion of the thermal imaging camera or the inner surface of the shutter for opening and closing the lens is used as a uniform surface. However, when a separate defocus optical system is added to the lens unit or a shutter for opening and closing the lens is used, there arises a problem of space limitation and cost increase of the thermal imaging camera by additional additional equipment. In addition, even when the lens portion of the thermal imaging camera is defocused to form a uniform surface, the actual focus position can be determined visually, whereas the actual defocus position can not be distinguished by the naked eye, There is a problem that it is difficult to do.

1 is a block diagram schematically showing a defocusing apparatus of an infrared ray detector according to an embodiment of the present invention. Fig. 2 is a view showing focus offset values of the first lens group and the second lens group at a low magnification, and Fig. 3 is a diagram showing focus offset values of the first lens group and the second lens group at a high magnification. 4 is a view showing a state in which defocus correction positions of the first lens group and the second lens group are determined.

Referring to FIG. 1, a defocus device of an infrared ray detector according to an embodiment of the present invention includes a first lens group L1 and a second lens group L2, A lens unit 100 for adjusting a magnification according to an interval between the two lens groups L2; A memory unit 200 for storing a focus setting position and a defocus setting position according to the magnification of the lens unit 100; An error measuring unit 300 for determining an actual focus position according to a magnification of the lens unit 100 and calculating focus offset values corresponding to a difference between the focus setting position and the actual focus position, respectively; A control unit (400) for determining a defocus correction position from the defocus setting position and the focus offset values; And a driving unit (500) for moving the first lens group and the second lens group to the defocus correction position, respectively.

The lens unit 100 adjusts the magnification according to the distance between the first lens unit L1 and the second lens unit L2. The first lens group L1 and the second lens group L2 may have a structure in which one or more lenses having various shapes are combined and the first lens group L1 and the second lens group L2 are the same And they can be disposed apart from each other on the optical axis. Further, the lens unit 100 may further include a lens group disposed in addition to the first lens group L1 and the second lens group L2, and may be configured to adjust the magnification according to the interval between the lens groups Various known techniques can be applied, and a detailed description thereof will be omitted.

The memory unit 200 stores a focus setting position and a de-focus setting position according to the magnification of the lens unit 100, respectively. For example, when the lens unit 100 is arranged at a low magnification position having a telephoto end or is arranged at a high magnification position having a wide angle end, the memory unit 200 may be arranged at a low magnification, The focus setting position of each of the first lens group L1 and the second lens group L2 at the focus setting position and the high magnification of the first lens group L1 and the second lens group L2, The defocus setting position of each of the first lens group L1 and the second lens group L2 can be stored. The memory unit 200 is a non-volatile storage device for storing data, and may be implemented as a semiconductor memory device such as a hard disk drive, a flash memory, an SD memory card, or the like.

The error measuring unit 300 determines the actual focus position according to the magnification of the lens unit 100 and calculates the difference between the focus setting position according to the magnification of the lens unit 100 stored in the memory unit 200 and the determined actual focus position (? 1_low,? 1_high,? 2_low,? 2_high) corresponding to the values of the focus offset values.

Referring to FIG. 2, the focus offset values? 1_low and? 2_low of the first lens group L1 and the second lens group L2 are calculated at a low magnification, The lens group L2 has a focus setting position (shown by a dotted line) of the first lens group L1 and a focus setting position (shown by a dotted line) of the second lens group L2 provided at the time of designing.

Such a focus setting position is a design position provided in the manufacturing process of each of the lens groups L1 and L2 and is an optical error due to the shape of each lens group L1 or L2 or a movement of each lens group L1 and L2 It does not reflect the mechanical error caused by Therefore, the focus setting position is different from the actual focus position of each lens group L1, L2.

The error measuring unit 300 measures the actual focus position of the first lens group L1 (shown by the solid line) and the actual position of the second lens group L2 from the focus setting position at the low magnification of each of the lens groups L1 and L2 And determines a focus position (shown by a solid line). The actual focus position may be determined by moving the position of each lens group L1 or L2 while observing it with the naked eye. Alternatively, the derivative value and the integral value of the detected contour line may be detected and automatically determined.

When the actual focus position at the low magnification is determined as described above, the error measuring unit 300 calculates the focus offset values (? 1_low,? 2_low) corresponding to the difference between the focus setting position and the actual focus position. That is, the error measuring unit 300 calculates the focus offset value? 1_low at the low magnification of the first lens group L1 and the focus offset value? 1_low at the low magnification of the second lens group L2 by the difference between the focus setting position and the actual focus position. The focus offset value? 2_low can be calculated.

Referring to FIG. 3, the focus offset values (? 1_high,? 2_high) of the first lens group L1 and the second lens group L2 are calculated at a high magnification. The lens group L2 also has a focus setting position (indicated by a dotted line) of the first lens group L1 and a focus setting position (indicated by a dotted line) of the second lens group L2 provided at the time of designing.

The error measuring unit 300 measures the actual focus position of the first lens group L1 (shown by the solid line) and the actual position of the second lens group L2 And determines a focus position (shown by a solid line). The actual focus position can be determined by moving the positions of the respective lens groups L1 and L2 while observing it with the naked eye. Alternatively, the derivative values and integral values of the detected contours may be determined by detecting the contours, Same as.

When the actual focus position at the high magnification is determined as described above, the error measuring unit 300 calculates a focus offset value (? 1_high,? 2_high) corresponding to the difference between the focus setting position and the actual focus position. That is, the error measuring unit 300 measures the focus offset value (? 1_high) at the high magnification of the first lens group (L1) and the focus offset value (? 1_high) at the high magnification of the second lens group The focus offset value? 2_high can be calculated.

The controller 400 determines a defocus correction position from the defocus setting position stored in the memory unit 200 and the focus offset values calculated by the error measuring unit 300. [ The defocus correction position is obtained by correcting the defocus setting position provided at the time of designing by reflecting an optical error due to the shape of each lens group L1 or L2 or a mechanical error caused by movement of each lens group L1 or L2 Position.

In order to reflect the optical errors and mechanical errors of the lens groups L1 and L2 at the defocus design position, the controller 400 controls the focus offset values (? 1_low,? 1_high,? 2_low,? 2_high Can be added to the defocus setting position of the first lens unit L1 and the defocus setting position of the second lens unit L2 to determine the defocus correction position. That is, the focus offset value? 1_low of the first lens unit L1 at the low magnification and the focus offset value? 1_high of the first lens unit L1 at the high magnification are set at the defocus setting position of the first lens unit L1, Focus correction position of the second lens unit L2 at the low magnification is added to the defocus setting position of the second lens unit L2 to determine the defocus correction position of the first lens unit L1, And the focus offset value (2_high) of the second lens unit (L2) at a high magnification can be added to determine the defocus correction position of the second lens unit (L2).

In order to improve the driving speed of the infrared ray detector, the controller 400 selects one of the focus offset values according to magnifications of the first lens group L1 and the second lens group L2, The offset value may be added to the defocus setting position stored in the memory unit 200 to set the defocus correction position.

That is, the focus offset value corresponding to the magnification of each lens group L1 and L2 varies depending on the sensitivity of the lens groups L1 and L2, and there is a difference in the optical error and the mechanical error range. Here, the sensitivity means the degree of change of the image formed according to the shape of each lens group L1 and L2 and the distance between the lens groups. Such sensitivity is determined by the lens groups L1 and L2 and the lens groups L1 and L2 ) May have different sensitivities depending on the magnification.

Therefore, the control unit 400 compares the sensitivities of the first lens group L1 and the second lens group L2 according to the magnification, selects the focus offset value for each lens group, and sets the selected focus offset value to the defocus setting Position to the defocus correction position.

For example, in the case of the first lens group L1, assuming that the sensitivity at a high magnification is higher than that at a low magnification and the sensitivity at a low magnification is lower than that at the high magnification in the case of the second lens group L2, 4, the control unit 400 adds the focus offset value? 1_high at the high magnification of the first lens group L1 to the defocus setting position (shown by the dotted line) of the first lens group L1, (Shown by a solid line) of the second lens group L2 is set to a defocus setting position (indicated by a broken line) of the second lens group L2, and a focus offset at a low magnification of the second lens group L2 Value to the defocus correction position (shown by the solid line) of the second lens group L2.

In this way, only the selected focus offset value among the focus offset values according to the magnifications of the first lens group L1 and the second lens group L2 is added to the defocus setting position of each lens group L1 and L2 according to the sensitivity By setting the defocus correction position, errors in the defocus setting position of the thermal imaging camera can be corrected efficiently and the driving speed can be improved.

The error measuring unit 300 further determines a temperature correction position corresponding to a temperature change of the lens unit 100 and further calculates a temperature offset value corresponding to a difference between the actual focus position and the temperature correction position, May set the defocus correction position to the focus setting position by reflecting the focus offset and the calculated temperature offset value.

In general, the infrared lens used in infrared detectors needs to be adjusted manually whenever the ambient temperature changes, because the focus of the lens changes. A special lens, an infrared athermal lens, can maintain an accurate focus regardless of ambient temperature changes, which does not require the user to adjust the focus separately, but it has a problem of high cost.

Therefore, it is possible to determine the temperature correction position, which is the position of the focus change according to the temperature change, with respect to each of the first lens group L1 and the second lens group L2, and determines the difference between the actual focus position and the determined temperature correction position It is possible to calculate the defocus correction position considering the focus change according to the temperature change by calculating the corresponding temperature offset value, adding the focus offset to the defocus setting position, and further adding the temperature offset value.

The error measuring unit 300 changes the temperature of the lens unit 100 to a constant temperature interval and outputs a temperature corresponding to each temperature The temperature offset values corresponding to respective temperatures are respectively calculated from the correction position and the calculated temperature offset values can be stored in the memory unit 200. [ Accordingly, the control unit 400 can determine the defocus correction position by reflecting the temperature offset value corresponding to the current temperature of the lens unit 100 from the respective temperature offset values according to the temperatures stored in the memory unit 200, to be.

The driving unit 500 moves the first lens group and the second lens group to the defocus correction position determined by the controller 400 according to the above-described configuration. The driving unit 500 may include any means for receiving an electric signal such as VCM (Voice Coil Motor), MEMS (Micro-Electro Mechanical Systems), stepping motor, etc. and transmitting the driving force to each of the first lens group and the second lens group have.

5 is a flowchart schematically illustrating a defocusing method of an infrared ray detector according to an embodiment of the present invention. The description of the defocusing method of the infrared ray detector and the defocusing apparatus of the infrared ray detector described above will be omitted.

5, a defocusing method according to an embodiment of the present invention includes storing a focus setting position and a defocus setting position according to a magnification of a lens unit including a first lens group and a second lens group, respectively (S100 ); A step (S200) of determining an actual focus position according to a magnification of the lens unit; Calculating a focus offset value corresponding to a difference between the actual focus position and the focus setting position (S300); (S400) of determining a defocus correction position from the defocus setting position and the focus offset values; And moving the first lens group and the second lens group to the defocus correction position, respectively (S500).

(S100) of storing a focus setting position and a defocus setting position, respectively, are stored in a memory section for storing data, at a focus setting position of each of the first lens group and the second lens group at a low magnification provided in designing the lens section, The focus setting position of each of the first lens group and the second lens group and the defocus setting position of each of the first lens group and the second lens group for defocus are stored.

In step S200, the actual focus position of each lens group reflecting the optical error due to the shape of each lens group or the mechanical error caused by the movement of each lens group may be visually observed, The autofocus method of FIG.

In step S300 of calculating the focus offset values, the focus offset values corresponding to the difference between the focus setting position and the actual focus position of the first lens group and the second lens group at the low magnification and the high magnification, respectively, are calculated. That is, when the actual focus position at the low magnification is determined, the error measuring unit calculates the focus offset value corresponding to the difference between the focus setting position and the actual focus position, and when the actual focus position at the high magnification is determined, And calculates a focus offset value corresponding to a difference between the position and the actual focus position.

The process of determining a defocus correction position (S400) is performed by reflecting the defocus setting position and the focus offset values. That is, all of the focus offset values corresponding to the magnification of the first lens group are added to the defocus setting position of the first lens group, and the focus offset values corresponding to the magnification of the second lens group at the defocus setting position of the second lens group are all In addition, the defocus correction position can be determined.

In addition, in order to improve the driving speed of the infrared detector, the step of determining the defocus correction position (S400) may include comparing sensitivity of each of the first lens group and the second lens group according to magnification; Selecting a focus offset value having the highest sensitivity among the focus offset values of the first lens group and the second lens group; And setting the selected focus offset value to a defocus correction position by adding the selected focus offset value to the defocus setting position of each of the first lens group and the second lens group.

That is, since the focus offset value according to the magnification of each lens group has a difference in error range according to the sensitivity of each lens group, the effect of correction of the focus offset value of the lens group having low sensitivity according to the magnification becomes insignificant. Therefore, a focus offset value having a high sensitivity is selected for each of the first lens group and the second lens group according to the magnification and is applied to the defocus setting position to determine the defocus correction position, It is possible to effectively correct the error and improve the driving speed.

The method of calculating the focus offset values (S200) may be performed at a predetermined temperature, for example, a state where the room temperature is maintained. According to an embodiment of the present invention, Determining a temperature correction position according to a temperature change of the lens unit to correct an error caused by the temperature change; And calculating a temperature offset value corresponding to a difference between an actual focus position and a temperature correction position, wherein the step of determining the defocus correction position further comprises: It can be determined as the correction position.

That is, as described above, since the focus of the lens changes according to the change of the ambient temperature, the lens used in the infrared detector calculates the focus offset values at the room temperature, It is possible to calculate an accurate defocus correction position by applying not only optical errors and mechanical errors but also errors due to temperature changes by determining the defocus correction positions reflecting the respective temperature correction positions.

Preferably, the process of determining the temperature correction position and the process of calculating the temperature offset value are repeated by changing the temperature of the lens unit to a predetermined temperature interval, and the process of determining the defocus correction position comprises: The defocus correction position can be set to reflect the temperature offset value corresponding to the current temperature of the lens unit among the temperature offset values of the temperature interval. Accordingly, the control unit can quickly determine the defocus correction position according to the temperature change by reflecting the temperature offset value corresponding to the current temperature of the lens unit from the respective temperature offset values according to the temperature stored in the memory unit.

In step S500 of moving the first lens group and the second lens group, if an accurate defocus correction position is determined by the above process, the first lens group and the second lens group are moved The defocus of the infrared ray detector is performed, and then a non-uniformity correction process for correcting the non-uniformity of the infrared ray detector can be performed.

While the preferred embodiments of the present invention have been described and illustrated above using specific terms, such terms are used only for the purpose of clarifying the invention, and the embodiments of the present invention and the described terminology are intended to be illustrative, It will be obvious that various changes and modifications can be made without departing from the spirit and scope of the invention. Such modified embodiments should not be individually understood from the spirit and scope of the present invention, but should be regarded as being within the scope of the claims of the present invention.

100: lens unit 200: memory unit
300: error measuring unit 400:
500:

Claims (9)

A lens unit including a first lens unit and a second lens unit, the lens unit adjusting a magnification according to an interval between the first lens unit and the second lens unit;
A memory unit for storing a focus setting position and a defocus setting position according to the magnification of the lens unit, respectively;
An error measuring unit for respectively calculating an actual focus position according to a magnification of the lens unit and calculating focus offset values corresponding to a difference between the focus setting position and the actual focus position;
The sensitivity of the first lens group and the second lens group is compared with each other to select one of the focus offset values of the first lens group and one of the focus offset values of the second lens group A control unit for adding a selected focus offset value to a defocus setting position of each lens group stored in the memory unit to determine a defocus correction position; And
And a driving unit for moving the first lens group and the second lens group to the defocus correction position, respectively.
delete delete The method according to claim 1,
Wherein the error measuring unit determines a temperature correction position according to a temperature change of the lens unit and calculates a temperature offset value corresponding to a difference between the actual focus position and the temperature correction position,
Wherein the control unit further determines the defocus correction position by further reflecting the temperature offset value.
Storing a focus setting position and a defocus setting position according to a magnification of a lens unit including a first lens group and a second lens group, respectively;
Determining an actual focus position according to a magnification of the lens unit;
Calculating focus offset values corresponding to a difference between the actual focus position and the focus setting position according to magnifications of the lens unit;
The sensitivity of the first lens group and the second lens group is compared with each other to select one of the focus offset values of the first lens group and one of the focus offset values of the second lens group Determining a defocus correction position by adding the selected focus offset value to a defocus setting position of each lens group stored in the memory unit; And
And moving the first lens group and the second lens group to the defocus correction position, respectively.
The method of claim 5,
Wherein the step of determining the defocus correction position comprises:
Comparing sensitivity of each of the first lens group and the second lens group according to magnification;
Selecting a focus offset value having the highest sensitivity among the focus offset values of the first lens group and the second lens group; And
And determining a defocus correction position by adding the selected focus offset value to a defocus setting position of each of the first lens group and the second lens group.
The method of claim 5,
Wherein the calculating of the focus offset values is performed while maintaining a constant temperature.
The method of claim 5,
Determining a temperature correction position according to a temperature change of the lens unit; And
And calculating a temperature offset value corresponding to a difference between the actual focus position and the temperature correction position,
Wherein the step of determining the defocus correction position further determines the defocus correction position by further reflecting the calculated temperature offset value.
The method of claim 8,
Wherein the step of determining the temperature correction position and the step of calculating the temperature offset value are repeated by changing the temperature of the lens unit at a constant temperature interval,
Wherein the defocus correction position is determined as a defocus correction position by reflecting a temperature offset value corresponding to a current temperature of the lens unit among temperature offset values of the predetermined temperature interval.

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