JPH028455Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a focusing device for a lens in an optical system of an imaging device.

In order to adjust the focus of the lens, conventional imaging devices prepare a reference test pattern, photograph this reference test pattern, and use a synchroscope to measure the degree of change in analog potential at the boundary between bright and dark signals of the photoelectrically converted video output signal. Visually check with waveform measurement means such as
The bright and dark signals projected on the synchroscope were the boundaries of the reference test pattern, and the position of the lens that caused the sharpest change in the potential of the analog video signal was defined as its optimal focal position.

The focus adjustment method of the conventional imaging device described above is the first method.
This will be explained with reference to FIGS. An image waveform of a reference test pattern 3 is derived using an optical system consisting of an image sensor 1 and a lens 2 shown in FIG. 1, and this waveform is observed on the screen of a synchroscope. The observed waveform is shown in FIG. 2, and waveform A shown by the solid line is the waveform at the focal point position of lens 2.
The waveform shown by the broken line B is the waveform at the out-of-focus position. Therefore, if the waveform observed with the synchroscope is the waveform shown by the broken line B, by adjusting the focus of the lens 2, the waveform becomes the waveform shown by the solid line A, and the focal position is set to the in-focus position. Can be done.

However, in the conventional focus adjustment method described above, adjustment is performed by visual observation of the waveform, so it is difficult to set the focused point position with high precision, and the setting of the focused point position varies depending on the adjuster. . Moreover, the boundary between the in-focus position and the out-of-focus position is delicate and difficult to adjust in a short time.

The purpose of this invention is to eliminate the drawbacks of the conventional focus adjustment method mentioned above, and to achieve high precision and less variation.
Furthermore, it is an object of the present invention to provide a focus adjustment device for an imaging device that can perform focus adjustment in a short time.

In order to achieve the above object, the focus adjustment device of the imaging device of this invention includes a threshold generator having a slope characteristic that linearly and continuously outputs threshold signals of different levels in time order, and a comparator that receives as input a threshold signal from a threshold generator and a single scan signal of a predetermined image from the video signal generator, compares these two signals, and outputs a binary signal; and a binary video signal processor for determining whether or not the focus position of the optical system is appropriate based on the number of bits of the binary signal output from the comparator.

This invention will be explained in detail below with reference to embodiments shown in the drawings.

FIG. 3 is a block diagram of an imaging device showing an embodiment of this invention. In the figure, 11 is an image sensor using a CCD or MOS type semiconductor element. 12 is an optical lens, and 13 is a reference test pattern arranged at the center of the field of view H and having sharp boundaries between bright and dark areas. The image sensor 11 is installed on the optical axis of an optical system consisting of an optical lens 12 and a reference test pattern 13, and an image of the reference test pattern 13 is formed on the image sensor 11. The imaged reference test pattern is photoelectrically converted by the image sensor 11, and one horizontal scanning signal is obtained. The photoelectrically converted signal is output by the video signal generator 14 as an analog video signal. This analog video signal is output as a focused output signal waveform A or an unfocused output signal waveform B, as shown in FIG. 4a, and is applied to one end of the input of the comparator 15. Note that waveform A in Figure 4a shows the OV level (dark area) from _t1 to _t2 .
period and t ₃ to _{t 4} period is Vv level period (light part) t ₂ to
The reference test pattern is configured so that the period t _{1 to} t ₂ and the period t ₃ to _{t 4} are sufficiently secured to be approximately equal to t 3 .

Reference numeral 16 denotes a threshold generator, and C in FIG.
As shown in the figure, the threshold value on the scan start side (t ₁ side) becomes the low potential VL, and the threshold value on the scan end side (t ₄ side) becomes the high potential _VH , which continuously changes linearly. Threshold values of the slope characteristics are sequentially generated over time and applied to one end of the input of the comparator 15. This threshold generator 16 is provided to binarize the output of the video signal generator 14.

The comparator 15 receives the analog video signal from the video signal generator 14 and the threshold signal from the threshold generator 16, and outputs an H signal when the analog video signal is larger than the threshold signal. If the analog video signal is smaller than the threshold signal, an L signal (0 level) is output, that is, the analog video signal is binarized and output as shown in FIGS. 4b and 4c.

The binarized output of the comparator 15, that is, the digitized video signal, is applied to a binarized video signal processor 17. Binarized video signal processor 1
7, the widths of dark and bright areas are digitally detected based on the applied binary video signal, and the suitability of focus adjustment is determined.

Next, the operation of adjusting the focus position in the embodiment circuit configured as described above will be explained.

First, assuming that the focus adjustment is properly made, the analog video signal output to the video signal generator 14 has the focused output signal waveform A shown in _FIG.
It has a steep waveform that rises at time t3 and falls at time _t3 . Therefore, in the comparator 15, the time point at which the analog video signal becomes greater than the threshold signal is _t2 . Conversely, the time point at which the analog video signal becomes smaller is _t3 . Therefore, the output of the comparator 15 becomes as shown in FIG. 4b. This binarized signal is added to the binarized video signal processor 17, and from t ₁
The number of dark bits D ₁ from t ₂ to t 2 , the number L ₁ of bright bits from t ₂ to t ₃ , and the number D ₂ of dark bits from t ₃ to t ₄ are counted. In this case, as described above, the time width from t ₁ to t ₂ and the time width from t ₃ to t ₄ are selected in advance to be equal, so D ₁ −D ₂ =0.

On the other hand, if the focus adjustment is not sufficient, the analog video signal output to the video signal generator 14 will be
The out-of-focus output signal waveform B shown in FIG. 4a is a waveform in which both shoulders of the reference test pattern are rounded. Therefore, in the comparator 15, the point in time when the analog video signal becomes greater than the threshold signal is:
t′ ₂ is earlier than t ₂ . Therefore, the output of the comparator 15 becomes as shown in FIG. 4c. This figure 4c
A video signal processor 17 converts the output signal shown in
In addition, we count the number of dark bits D' ₁ , the number of bright bits L' ₁ , and the number of dark bits D' ₂ and calculate |D' ₁ −D' ₂ |=. Since D' ₂ >D' ₁ , we get some The difference output is obtained. This difference output |D′ ₁ −D′ ₂ | tends to increase as the focus shift increases. Therefore, by displaying this difference |D' ₁ -D' ₂ | on a digital display or the like and reading it, it is possible to know the degree of shift in the focal position.

When the out-of-focus output signal waveform B approaches the in-focus output signal waveform by performing focus adjustment, the number of dark bits D' ₁ becomes D1, and the number of bright bits L' ₁ becomes _D1 .
The number of dark bits D' ₂ approaches L ₁ and D ₂ , respectively, and when the in-focus position is reached, D ₁ =D ₂ . Therefore, if the focal point position is set at |D ₁ −D ₂ |=0, it can be adjusted to the in-focus position, and D ₁ =
You can tell that the focus adjustment is completed at the _D2 position.

In addition, to recognize D ₁ = D ₂ , instead of using a digital display,
A display lamp may be turned on or a warning sound may be emitted by a buzzer upon a matching output of D ₁ =D ₂ .

Also, instead of recognizing the dark bit _D1 = _D2 , the dark bit _D1 , light bit _L1 , etc. are set in advance.
The focal point position may be determined by recognizing D ₁ =D′ ₁ and L ₁ =L′ ₁ .

Further, in the above embodiment, a case has been described in which the center waveform of the reference test pattern is a bright portion, but instead of this, a reference test pattern may be used in which the center is a dark portion and the periphery is a bright portion.

Furthermore, although the above embodiment describes the case where the focus position of the lens is adjusted, the focus adjustment device of this invention can also be applied to fixing the lens position and adjusting the focus position when adjusting the optical axis of an image sensor. can.

Furthermore, in the above embodiment, a line sensor is used to convert the optical image into an electrical signal, but
Instead of this, a two-dimensional surface sensor or an image pickup tube is used to select a specific scanning line, and the selected one
The same processing as in the above embodiment may be applied to the scanning line.

As described above, according to the focus adjustment device of the imaging device of this invention, the bits of the binary signal output obtained by comparing a predetermined reference pattern video signal with a threshold signal having temporally different slope characteristics. Since the suitability of the focal point position is determined based on the number of points, the focal point position can be determined electronically, allowing for highly accurate adjustment with less variation in adjustment, and in addition, a focus adjustment device that takes less time to adjust. Obtainable. In addition, the adjustment work can be automated and mechanized, contributing to improved production efficiency of imaging devices.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an outline of an optical system for explaining a focus adjustment method in a conventional imaging device, FIG. 2 is a video signal waveform diagram also for explaining a focus adjustment method in a conventional imaging device, and FIG. The figure is a block diagram of an image pickup apparatus showing an embodiment of this invention, and FIG. 4 is a signal waveform diagram for explaining the operation of the image pickup apparatus shown in FIG. 3. 11: Image sensor, 12: Optical lens, 1
3: Reference test pattern, 14: Video signal generator, 15: Comparator, 16: Threshold generator, 1
7: Binarized video signal processor.

Claims (1)

[Claims for Utility Model Registration] An imaging device that includes an optical system including a lens, and a video signal generator that converts an optical signal from the optical system into an electrical signal through scanning processing to obtain a video signal of an image to be photographed. , a threshold generator having a slope characteristic that linearly and continuously outputs threshold signals of different levels in time order, and a threshold signal from this threshold generator and the video signal generator. a comparator that receives as input a scanning signal for one scan of a predetermined image of the optical system, compares these two signals, and outputs a binary signal; 1. A focus adjustment device for an imaging device, comprising a binarized video signal processor that performs judgment processing based on the number of output bits.