JPS62209966A - Focus adjustment system - Google Patents

Abstract

PURPOSE:To obtain a focused position at high accuracy and high reliability by performing focus adjustment actions several times, calculating the average of plural focused positons and setting it to a focused position if the difference between the maximum and minimum positions for moving a lens among obtained plural focused positions is lower than a set value regarding the depth of a permissible focus. CONSTITUTION:A focus adjusting lens 4 is vertically displaced by an eccentric cam 13 coaxially fitted on a stepping motor 12, and its upper-most and lower- most positions are detected when a rotating light shielding plate 14 passes by a photointerrupter 15A or 15B. In that case each detection focused position is obtained from data when a maximum peak is detected and data when a minimum peak is detected in terms of data obtained from plural focus detection actions. If the focused positions are within the range of the focus depth, their average is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus adjustment method, and more particularly to a focus adjustment method in a microfilm reader device or the like having an automatic focus adjustment function.

[Conventional technology]

Conventionally, this type of film reader device requires high accuracy in its focus adjustment, but at the same time it must also be able to obtain a highly reliable focused point. FIG. 4 shows an example of the configuration of this type of film reader in which an image on a microfilm is electronically read, where F is the microfilm and f is its projected image.

The image on the film F is illuminated by light guided from a light source 1 through a lens 2 and a mirror 3, and passes through a focusing lens 4 and a half mirror 5 to a photodetector 6 having light receiving elements arranged in a line. be guided. A carriage 7 carrying the photodetector 6 is slidably held on a guide shaft 8, and a wire 9 attached to the carriage 7 is driven by a pulley 10 and a motor 11 to convert the photodetector 6 into a projected image. Reading can be performed by sub-scanning along f.

The focusing lens 4 is moved up and down by a stepping motor 12, and as will be described later, an eccentric cam (not shown here) is coaxially attached to the stepping motor 12, and the lens 4 is moved up and down via the eccentric cam. It can be displaced up and down with each rotation of the motor 12. Further, a focus detector 20 is disposed above the half mirror 5 at a position equal to the optical path length from the image on the microfilm F to the projected image f.
0, and the automatic focus adjustment operation will be described below with reference to FIGS. 5 and 6.

The focus detector 20 is equipped with a beam splitter (a type of prism, shown conceptually in FIG. 7) that separates the light beam into two as shown in FIG. A first photodetector S1 is installed at a position with a long optical path length, and a second photodetector S2 is installed at a position with a long optical path length. Therefore, a part of the projection light reflected by the half mirror 5 after passing through the focus adjustment lens 4 is guided directly from the half mirror to the focus detector 20, and the lens 4 is connected to the stepping motor as described above. 12, the contrast values of the output signals from the photodetectors S1 and S2 are expressed by curves C51 and C as shown in FIG.
52 is obtained.

As is clear from this figure, these curves C5□ and CS2 each have a contrast value according to a specific phase distribution, so the respective maximum values P1 and P2
can be found. Therefore, automatic focus adjustment has been performed such that the center point of the lens position where these maximum values P1 and P2 are obtained is determined as the focal point position.

However, in the case of such a focus adjustment method, when the stepping motor 12 is driven to vertically displace the lens 4, the contrast value curve actually obtained has a ripple wave as shown in FIG. The value, that is, the peak value, becomes unstable. This means that
Vibration noise generated from the stepping motor 12, power fluctuations when driving the motor 12 step by step, ripple fluctuations generated from the device cooling fan and the power supply itself, noise from the semiconductors themselves of the photodetectors S1 and S2, and external noise. This is due to the superposition of noise such as electrostatic or discharge noise, and electromagnetic noise.
and the detected maximum value P.

There is a possibility that a positional deviation of 2 occurs between the in-focus point position obtained from P2 and P2, and the correct in-focus point cannot be obtained.

(Problems to be Solved by the Invention) The purpose of the present invention is to eliminate the above-mentioned drawbacks, repeat the focus detection operation at least twice, and determine the focused point position by appropriate calculation from the obtained data. It is an object of the present invention to provide a focus adjustment method that is more accurate and reliable than the conventional one.

[Means for solving problems]

In order to achieve this purpose, a focus adjustment method is used in which one or more light receiving elements detect projection light obtained from a read image through an optical member, and the focus position is determined based on the obtained data and the focus is adjusted. , the focus adjustment is performed multiple times, and the maximum first position of the multiple focus positions obtained is
The focal position and the minimum second focal position are determined, and when the moving distance between the first focal position and the second focal position does not exceed a predetermined tolerance, at least the first focal position and the second focal position are determined. The feature is that the focal position is determined by

[For production]

According to the focus adjustment method of the present invention, each detected in-focus point is determined from data obtained when the maximum peak is detected and data when the minimum peak is detected among data obtained from multiple focus detection operations. If these focal positions are within the range of the depth of focus, the lens can be moved to a more accurate focal position by simple steps and calculations such as calculating the average focal position from these focal focal positions. The reliability of the focus adjustment can be further increased.

〔Example〕

Embodiments of the present invention will be described in detail and specifically below based on the drawings.

FIG. 1 shows a focus adjustment device for implementing the invention,
The focus adjustment lens 4 is vertically displaced by an eccentric cam 13 coaxially attached to a stepping motor 12, and its uppermost and lowest positions are when the rotating tip plate 14 passes the position of the photointerrupter 15A or 15B. is detected.

Further, in this example, focus detectors 6^, 6B, and 6C are provided for selecting points so that greater contrast can be obtained depending on the state of the image, and these selections can be made by a changeover switch SW. In this way, the output signal from the focus detector selected from among the focus detectors 6A to 6C is amplified by the amplifiers AS1 and AS2, respectively, and further converted into a digital signal by the A/D converter AD, and then sent to the central processing unit CPU. stored in memory and CPU
The calculation is performed in Furthermore, the stepping motor 12 can be driven in steps by the drive signal from the CPU via the driver SD.

Now, when the method of the present invention is implemented using such a focus adjustment device, the CPU can obtain data as shown in FIG. 2, for example. That is, in this example, the focus detection operation is performed three times, and as described above, the lens 4 is moved up or down step by step by the stepping motor 12 to detect the light in any of the focus detectors 6A to 6C. By inputting the output signals from the detectors S1 and S2 into the memory, the curves C5■ and C5I□, CS, and CS, 2) C53I and CS3. Three sets of are obtained.

Therefore, first, calculate the maximum peak values pH and PI3 from the set of curves CS, , and C512, and similarly calculate the maximum peak value P2 from the remaining set of curves.
1 and P22) Find P3□ and P32.

Thus, next, find the midpoint LAI of lens positions 111 and L12 corresponding to the maximum peak value pH and PI3,
Similarly, the midpoint LA2 of lens positions L21 and L22 is determined from the maximum peak values P21 and P22, and the lens position Ljl is determined from the maximum peak values P21 and P22.
Find the midpoint of l and L2□, find A2, and find the midpoint LA of these
The averaged position of I, LA2, and LA3 is set as the in-focus position LA.

However, the three focal positions LAI obtained as in this example
, L^2 and L^3 each contain the noise component described above. Therefore, in the process of the above calculation, the difference between the maximum depth position (for example, L) and the minimum depth position (L31 Lll in the figure) among the lens positions where the peak value occurs is calculated, and that difference is set in advance. As described above, the focal position determined three times LAI x
The averaged focal point position of LA2 and L^3 is determined, and if the above-mentioned L31 Lll is larger than the above set value, the same series of focus detection operations and calculations are repeated three more times. shall be taken as a thing.

In addition, if the above-mentioned detected focal depth difference is larger than the set value even after repeating the focus detection operation again, it is possible that the main unit itself is malfunctioning or the focus adjustment device is malfunctioning, so for example, an alarm may be issued. A method is to be taken to either cause the problem to occur or to display a serviceman call.

Figure 3 shows the focus adjustment procedure described above.
First, in step S1, the stepping motor 12 is driven to set the focusing lens 4 at the starting point, that is, at the lowest position of the lens. Next, in step S2, the motor 12 is driven one step to displace the lens 4 upward by that amount, and the process proceeds to step S3, where the photodetectors S1 and S2 of the focus detector 6 (any one of 6A to 6C) The data is stored in the memory according to the output signal.

Next, the process proceeds to step S4, where it is determined whether or not the focus adjustment lens 4 has reached the end point, that is, the highest position.If the focus adjustment lens 4 has not reached the highest position, the above-mentioned step-by-step walk and measurement (52 to S3) are performed. When the focus adjustment operation is repeated and the uppermost position is reached, it is determined in the next step S5 whether or not the same focus adjustment operation has been repeated a predetermined number of times.

When the focus adjustment operation has been repeated a predetermined number of times in this way, the process proceeds to step S6, and the peak values of the curves C5++ to C53□ and C522 to C5,2 are determined from the data stored in the memory, and these peak values are determined in step S7. From the lens positions L11 to L31 and L12 to 132 where the values were obtained, the midpoints of fa L + + and L12 LAI, L2+
and 122 midpoint LA2) midpoint LA3 between L31 and L32
Perform the calculation to find .

Next, in step S8, the difference between the maximum depth position and the minimum depth position among these midpoints LAI, LA2, and LA3 is determined, and in step S9, it is determined whether the value of the difference is greater than or equal to a predetermined value. If the value is greater than or equal to the predetermined value, step 51
The process branches to step 2, where it is determined whether or not such a predetermined value or more has been repeated, and if it has been repeated, a warning is issued in step 513 and the adjustment is stopped. Also,
Step S1 if not repeated in step 512
Return to and repeat the same adjustment operation.

Furthermore, if the above-mentioned difference value has not reached the predetermined value in step S9, the process proceeds to step SIO and the midpoint LAI s
An average lens midpoint position LA of LA2 and LA3 is calculated, and in step Sll, this lens position LA is set as the in-focus position, and the focusing lens 4 is set at this position.

Although the above explanation deals with the case where the focus adjustment operation is performed multiple times for one specific position on the image, the application of the present invention is limited to such an adjustment operation of only one point. Instead, by further performing a series of focus adjustment operations at different positions on the image, it is possible to prevent partial blurring of the image and to expect a more accurate focus adjustment effect.

Furthermore, in the image reading device, the image reading sensor can also be used as a focus detection sensor.

〔Effect of the invention〕

As described above, according to the present invention, the focus adjustment operation is performed a plurality of times, the focus position is determined based on the data obtained from the focus detection means for each focus adjustment operation, and the determined focus position is If the difference between the maximum and minimum positions of lens movement among the positions is smaller than the value set in relation to the allowable depth of focus, calculate the average position of the plurality of focal positions and use this as the in-focus position. This has significantly improved the accuracy of focal position detection in conventional methods due to the superimposition of various noises on the detection signal, making it possible to obtain a highly accurate and reliable focal position. .

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of the configuration of a focus adjustment device for carrying out the present invention, and FIG. 2 is a curve showing an example of the positional relationship between data and calculated elements when determining a focal position according to the present invention. Fig. 3 is a flowchart showing the procedure for carrying out the present invention, Fig. 4 is a perspective view showing an example of the configuration of a conventional microfilm reader device to which the present invention can be applied, and Fig. 5 is a focus adjustment device thereof. A schematic diagram of the configuration, Figure 6 is a curve diagram showing the ideal relationship between the contrast obtained by the focus adjustment device in Figure 5 and the focal position, and Figure 7 is a curve diagram showing the relationship between the contrast and focal position actually obtained. It is a curve diagram showing an example. DESCRIPTION OF SYMBOLS 1... Light source, 4... Focus adjustment lens, 5... Half mirror 1 6, 6A, 6B, 6C... Photodetector, 11... Motor, 12... Stepping motor, S , , S2... Photodetector, 13... Eccentric cam, 14... Front plate, 15A, 15B... Photo interrupter, F... Film, f... Projection image, cpu. ...Central processing unit, C5++~C531, (:S12~C532...Contrast curve, pH-P31+PI□~P32...Peak value, L
11~L3++L21~L32...Lens position, LA
l+LA2+LA3...Detected focus position, L...True focus position, LA...Focus position. Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] 1) A focus adjustment method in which one or more light-receiving elements detect projection light obtained from a read image via an optical member, and the focus position is determined based on the obtained data and the focus is adjusted. Performing the focus adjustment a plurality of times, determining a maximum first focal position and a minimum second focal position among the plurality of focal positions obtained, and determining the first focal position and the second focal position. A focus adjustment method characterized in that a focus position is determined based on at least the first focus position and the second focus position when the moving distance between the two does not exceed a predetermined tolerance value. 2) In the focus adjustment method according to claim 1, when the distance exceeds the predetermined tolerance,
A focus adjustment method characterized by performing the focus adjustment a plurality of times again. 3) A focus adjustment method according to claim 1 or 2, characterized in that a warning is generated when the distance exceeds the predetermined tolerance. 4) The focus adjustment method according to any one of claims 1 to 3, wherein the focus adjustment is performed a plurality of times at different positions on the read image. 5) A focus adjustment method according to claim 1, characterized in that the focus is adjusted to an average position between the first focus position and the second focus position.