Method for adjusting lens offset of a video camera

A method for adjusting the lens offset of a video camera, in which the offset value of the lens is calculated quickly and exactly during only a small travel of a focus lens and a zoom lens, thereby shortening the time required for calculating the offset value conventionally involving a large travel of the focus lens and the zoom lens, preventing an error, and further curtailing the cost of production.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method for adjusting a lens offset of a 
video camera, and particularly to an improved method for adjusting a lens 
offset capable of advantageously adjusting the offset value of the lens 
through small travel of a focus lens and a zoom lens. 
2. Description of the Conventional Art 
Referring to FIG. 1, there is shown a block diagram of a conventional video 
camera. As shown in the drawing, the conventional video camera includes a 
lens group 10 having a focus lens and a zoom lens; an iris 20 for 
controlling the light quantity incident from the lens group 10; a vidicon 
30 for forming an optical image of an object incident through the iris 20 
and convening the image into multiplexed chrominance signals; a .sampling 
and gain control unit 40 for dividing the multiplexed chrominance signals 
outputted from the vidicon 30 into luminance signals and color signals, 
and controlling the gains thereof; a video signal processing unit 50 for 
encoding the luminance signals and the color signals outputted from the 
sampling and gain control unit 40 and outputting composite video signals; 
a focus evaluation calculating unit 60 for receiving the luminance signals 
outputted from the sampling and gain control unit 40 and calculating the 
focus evaluation corresponding to a region of the screen; and a key input 
unit 100 for selectively inputting the general operations of the video 
camera. The conventional video camera further includes a microprocessor 70 
for adjusting the offset value of the lens according to the key data 
selected in the key input unit 100 and according to the evaluation value 
outputted from the focus evaluation calculating unit 6, and performing the 
control operation; a motor driving unit 80 for driving the lens group 10 
according to the control signals of the microprocessor 70; and an iris 
driving unit 90 for controlling the opening amount of the iris 20. 
Referring to the drawings, the operation of the conventional video camera 
with the above-described construction will be explained. 
First, as shown in FIG. 1, when an optical image of an object is incident 
upon the vidicon 30 through the lens group 10 and the iris 20, the vidicon 
30 forms an optical image of the object and outputs the image after 
converting it into the multiplexed chrominance signals. 
Next, the sampling and gain control unit 40 receives the multiplexed 
signals outputted from the vidicon 30, and divides the signals into 
luminance signals and color signals. After signal division, the sampling 
and gain control unit 4 controls the gains thereof and outputs them to the 
video signal processing unit 50. The luminance signals and the color 
signals received by the video signal processing unit 50 are encoded into a 
composite video signal and outputted. 
The focus evaluation calculating unit 60 receives the luminance signals 
from the sampling and gain control unit 40, and calculates the focus 
evaluation by detecting the amount of the high frequency component of the 
luminance signals within a region of the image. After calculation, the 
focus evaluation calculating unit 60 outputs the focus evaluation values 
to the microprocessor 70. 
That is, if the focus is correctly adjusted, the high frequency component 
of the luminance signal reaches its maximum (the focus evaluation is 
large), while, if the focus is not correctly adjusted, the high frequency 
component of the luminance signals becomes small (the focus evaluation is 
small). 
Therefore, the microprocessor 70 receives the focus evaluation values 
outputted from the focus evaluation calculation unit 60, and controls the 
motor driving unit 80 to perform an auto-focusing operation. 
At this time, when a user pushes the function key through the key input 
unit 100, the microprocessor 70 calculates the offset value by comparing 
the theoretical trace curve of FIG. 2 set by the predetermined lens spec 
values Wx, Wy, Tx and Ty with the actual trace curve formed by moving the 
positions of the zoom lens and the focus lens, and controls the offset of 
the lens group 10. 
Referring to FIGS. 3 and 4, the method for calculating the offset values of 
the focus lens and the zoom lens will now be described in detail. 
First, when a user pushes the zoom key through the key input unit 100, the 
microprocessor 70 moves the position of the zoom lens of the lens group 10 
by as much as the theoretical value Wx away from a start point, by driving 
the motor driving unit 80 (step 102). 
Next, the microprocessor 70 drives the motor driving unit 80 and moves the 
position of the focus lens of the lens group 10 away from the start point. 
And then, the microprocessor 70 seeks the focusing position and stores the 
position as the first position f1 of the focus lens (step 104). 
Thereafter, the microprocessor 70 drives the motor driving unit to move the 
position of the focus lens of the lens group 10 by as much as the 
theoretical value Ty toward the start point by driving the motor driving 
unit 80 (step 106). Again, the microprocessor 70 seeks the focusing 
position by moving the position of the zoom lens from that position toward 
the long-distance position and stores the focusing position as the first 
position z1 of the zoom lens (step 108). 
After moving the position of the zoom lens by as much as the theoretical 
value Tx toward the start point (step 110), the microprocessor 70 moves 
the position of the focus lens toward the long-distance position, seeks 
the focusing position, and stores the position as the second position f2 
of the focus lens (step 112). 
As shown above, when the first and second positions f1 and f2 of the focus 
lens are obtained, the microprocessor 70 calculates an absolute value by 
subtracting the value of the second position f2 from the value of the 
first position f1. The obtained absolute value is compared with the 
predetermined threshold value (step 114). 
If the calculated absolute value is larger than a threshold value, the 
microprocessor 70 stores the value of the second position f2 of the focus 
lens as the value of the first position f1 of the focus lens (step 116), 
and repeatedly performs the operations after step 104. Whereas, if the 
calculated absolute value is smaller than the threshold value, the 
microprocessor 70 compares the first and second positions f1 and f2 of the 
focus lens and the position of the zoom lens, which are calculated from 
the actual trace curve E, with the data detected from the theoretical 
trace curve A, and calculates the offset value (step 118). 
However, the conventional method for adjusting the lens offset of the 
conventional video camera has disadvantages, in that it takes much time to 
calculate the offset value due to much travel of the focus lens and the 
zoom lens, and errors are easily committed as the motor for driving the 
focus lens and the zoom lens is frequently driven. 
SUMMARY OF THE INVENTION 
Therefore, it is an object of the present invention to provide a method for 
adjusting a lens offset which controls quickly and exactly the offset 
value of the lens through small travel of a focus lens and a zoom lens. 
To achieve the above object, the present invention includes a first step 
for seeking the focusing positions i.e., the first and second positions of 
the zoom lens by moving the position of the focus lens by as much as the 
theoretical value away from the start point and moving the position of the 
zoom lens toward its long-distance position away from the start point; a 
second step for seeking the focusing point by moving the focus lens toward 
the long-distance position after moving the zoom lens to a middle point 
between the first and second positions of the zoom lens; a third step for 
seeking the focusing positions i.e., the third and fourth positions z3 and 
z4 of the zoom lens by moving the zoom lens from the first position z1 to 
the second position z2; and a fourth step for calculating an absolute 
value by subtracting the value of the fourth position z4 from the value of 
the third position z3, and calculating an offset value representing a 
focus position by comparing the absolute value with a predetermined 
threshold value.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A method for adjusting a lens offset for a video camera in accordance with 
the present invention will now be described, referring to the drawings. 
First, as shown in FIG. 1, when an image of the object is incident upon a 
vidicon 30 through lens group 10 and iris 20, the vidicon 30 forms the 
image of the object and converts the image into the multiplexed 
chrominance signals. 
Next, sampling and gain control unit 40 receives the multiplexed signals 
outputted from the vidicon 30, and divides the signals into luminance 
signals and color signals. After signal division, the sampling and gain 
control unit 40 controls the gains thereof and outputs them to video 
signal processing unit 50. The luminance signals and the color signals 
received by the video signal processing unit 50 are encoded into a 
composite video signal and outputted. 
The focus evaluation calculating unit 60 receives the luminance signals 
having a high frequency component from the sampling and gain control unit 
40, and calculates a focus evaluation value by detecting the amount of 
high frequency component in the luminance signals within a region of the 
image. After calculation, the focus evaluation calculating unit 60 outputs 
the focus evaluation value to microprocessor 70. 
Therefore, the microprocessor 70 receives the focus evaluation value 
outputted from the focus evaluation calculation unit 60, and controls 
motor driving unit 80 to perform an auto-focusing operation. 
The method for calculating the offset value of the focus lens and the zoom 
lens will be explained, referring to FIGS. 5 to 7. 
First, when a user pushes the zoom key through the key input unit 100, the 
microprocessor 70 moves the position of the focus lens of the lens group 
10 by as much as the theoretical value Wy/2 away from a start point by 
driving the motor driving unit 80 (step 202). 
Next, the microprocessor 70 moves the position of the zoom lens of the lens 
group 10 toward its long-distance position away from the start point by 
driving the motor driving unit 80. And then, the microprocessor 70 seeks 
the focusing positions and stores the positions as the first and second 
positions z1 and z2 of the zoom lens (step 204). 
The microprocessor 70 places the zoom lens at the middle point z3 between 
the first and second positions z1 and z2 of the zoom lens by moving again 
the zoom lens of the lens group 10 towards the start point (step 206). And 
then, the microprocessor 70 seeks the focusing point by moving the focus 
lens toward its long-distance position (step 208). 
Thereafter, the microprocessor 70 seeks the focusing points by moving the 
zoom lens of the lens group 10 from the first position z1 to the second 
position z2, and stores the focusing positions as the third and fourth 
positions z3 and z4 of the zoom lens (step 210). 
As described above, when the third and fourth positions z3 and z4 of the 
zoom lens are obtained, the microprocessor 70 calculates an absolute value 
by subtracting the value of the fourth position z4 from the value of the 
third position z3. The obtained absolute value is compared with a 
threshold value (step 212). 
If the absolute value is judged larger than the predetermined threshold 
value, the microprocessor 70 stores the value of the third position z3 of 
the zoom lens as the value of the first position z1 of the zoom lens, and 
also stores the value of the fourth position z4 as the value of the second 
position z2 of the zoom lens (step 214). And then, the microprocessor 70 
performs again the operations from steps 206 to 212. 
Whereas, if the absolute value is judged smaller than the predetermined 
threshold value, as shown in FIG. 6, the microprocessor 70 calculates the 
offset values Ox and Oy by comparing the position of the apex of the 
actual trace curve D with the position of the apex of the theoretical 
trace curve C, and finishes the operation (step 216). 
Therefore, the microprocessor 70 drives the motor driving unit 80 to adjust 
the offset value of the focus lens and zoom lens of the lens group 10 
according to the offset values Ox and Oy. 
As hereinbefore described, according to the present invention, the offset 
value of the lens is calculated quickly and exactly during only a small 
travel of the focus lens and the zoom lens, and thereby an error can be 
prevented and the cost of production is curtailed by shortening the time 
required for calculating the offset value.