JP3529546B2 - Document reading device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document reading device, and more particularly to correction of an optical axis shift depending on a position on a document surface, and is applied to, for example, a reading device of a copying machine or a scanner as a personal computer input device. It is possible.

[0002]

2. Description of the Related Art In a document reading device used in a reading device of a copying machine or a scanner as a personal computer input device, it is very important to make the reading values uniform and stable at each place on the document surface. is there. When reading a document with uniform density, if the amount of light received on the image forming surface differs depending on the reading position, the light receiving element installed on the light receiving surface is a photoelectric conversion element such as a CCD or a photoreceptor of an analog copying machine. Regardless of whether or not there is such, the density of the read image becomes uneven, and the background is stained, and in the case of a color image forming apparatus, a defect such as a gray balance failure occurs.

Therefore, as described in JP-A-60-113232, JP-A-60-218970, etc., the read value is obtained by detecting the light quantity of the image plane and controlling the light quantity of the light source. Is generally performed. In addition, Japanese Patent Application No. 8-5 related to the applicant's application
In the specification and drawings attached to the application of No. 9629, a chart of uniform density is set outside the image reading range on the document surface or on the same plane, the chart is read, and density unevenness is detected from the output value. , The amplification factor of the analog circuit amplifier,
Alternatively, the reference voltage of the A / D converter may be corrected according to the density unevenness so that the density unevenness does not occur in the formed image.

[0004]

As described above,
In the conventional document reading apparatus, density unevenness in document reading becomes a problem, and various techniques for correcting this have been proposed. However, in the document reading device, not only the density unevenness of the document reading, but also the relative displacement between the reading sensor and the optical axis of the optical system on the image forming surface greatly affects the performance of the formed image. To do. That is, the deviation of the optical axis of the optical system with respect to the reading sensor causes problems such as not only variations in reading values (uneven reading density) depending on places as described above but also magnification errors in the scanner moving direction (sub-scanning direction). .

The present invention has been made in view of the above prior art, and the inventions according to claims 1 and 3 correct the optical axis deviation to improve the unevenness in reading density and the magnification error in the sub-scanning direction. An object of the present invention is to provide a document reading device capable of performing the above. The invention according to claim 1 also has the above object.
At the same time, the correction of the optical axis deviation is reflected when reading the actual image.
The method is to synchronize the reading drive source and shift the optical axis.
The correction means is moved at a speed corresponding to
Therefore, it does not have a new drive source and it can perform accurate correction.
The purpose is to provide a document reading device that can
It

According to a second aspect of the present invention, when a 3-line color CCD is used as the reading sensor, the optical axis shift is detected by recognizing the ratio of the magnitudes of the output values of the 3-lines. It is an object of the present invention to provide an original reading device capable of detecting the deviation amount of the optical axis with a simple structure without using any special means.

According to a fourth aspect of the present invention, the optical axis shift is detected by recognizing the magnification error in the sub-scanning direction, whereby the shift amount of the optical axis can be determined with a simple structure without using any special means. An object of the present invention is to provide a document reading device that can detect the original document.

[0008]

According to a fifth aspect of the present invention, a function for detecting the amount of optical axis deviation is provided in the document reading apparatus, so that even if the optical axis deviation amount changes under use conditions or changes over time, a service person or It is an object of the present invention to provide a document reading apparatus that enables a user to correct an optical axis shift, thereby enabling the latest and optimum correction.

[0010]

The invention according to claim 1 is
A light source that illuminates the document surface, a reading sensor that consists of a large number of photoelectric conversion elements that optically read the reflected light from the document and photoelectrically converts it, an optical system that guides the reflected light from the document to the reading sensor, and a reading In a document reading apparatus having a reading drive source that relatively moves a reading position of a document surface by a sensor, when the reading position is relatively moved, a detection unit that detects a deviation amount of an optical axis of an optical system, when reading the original <br/> manuscript by the reading sensor, to have a correction means for correcting the deviation of the positional relationship by relatively moving the reading sensor to the optical axis in accordance with the detected the deviation amount, the correction means Document as a driving source of
A reading drive source that moves the reading position relative to the surface
Share the movement of the driving source of the correction means and the movement of the reading driving source
It is characterized in that it is configured to synchronize .

According to a second aspect of the present invention, in the first aspect of the invention, the reading sensor is a three-line color image sensor, and in order to detect the amount of deviation of the optical axis, the magnitude of each output of the three lines is determined. It is characterized by being recognized.

According to a third aspect of the invention, the surface of the original is illuminated.
The light source and the reflected light from the original are optically read and photoelectrically converted.
A reading sensor consisting of many photoelectric conversion elements that can be replaced
An optical system for guiding the reflected light from the
Reading by moving the reading position of the document surface by the sensor relatively
In a document reading device having a take-up drive source, a reading sensor
When moving the scanning position on the document surface by
Detecting means for detecting the deviation amount of the optical axis of the academic system, and a reading sensor
When scanning an original with the
Move the axis and the reading sensor relatively to shift the positional relationship.
And a correction means for correcting, and as a driving source of this correction means
A pair of models that independently control the left and right heights of the reading sensor.
It is characterized by having independent data.

According to a fourth aspect of the present invention, in the first aspect of the invention, the detecting means is based on a magnification error in the moving direction.
It is characterized in that the amount of deviation of the optical axis is detected .

The invention according to claim 5 is the invention as claimed in claims 1, 2, and 3.
Alternatively, the invention described in 4 is characterized in that detection means for detecting the amount of deviation of the optical axis is provided in the apparatus.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a document reading apparatus according to the present invention will be described below with reference to the drawings.
FIG. 5 is a mechanical view of a general document reading apparatus as viewed from the side. Focusing on the optical system, first there is a light source 1 including a halogen lamp, a reflector 2, and a first scanner 5 on which the light source 1 and a first mirror 3 are mounted. First scanner 5
While illuminating the image surface of the document placed on the contact glass 6 with the image surface facing downward and pressed against the contact glass 6 by the pressure plate 7 with the illumination light of the light source 1, at a constant speed in the drawing. You can move to the right. Next, a second mirror having a second mirror 8 and a third mirror 9
There is a scanner 10. The second scanner 10 moves to the right at a speed that is exactly half that of the first scanner 5. As a result, regardless of the position of the first scanner 5 with respect to the document surface, the distance (object distance) from the document surface to the center of the lens 11 described later is constant.

In optical imaging, the reflected light from the original surface is received by the first mirror 3, is reflected by the second and third mirrors 8 and 10 one after another, enters the lens 11, and is refracted by the lens 11 to be reflected by the lens 11. It is incident on a charge-coupled device (hereinafter referred to as “CCD”) 12 as a reading sensor, which is located at a distance (image plane distance) from which the image is formed, and an image of the original surface is formed on the light receiving surface of the CCD 12. It is designed to be done. The CCD 12 is composed of a large number of photoelectric conversion elements (charge-coupled elements) that optically read the reflected light from the document and photoelectrically convert it. Here, the second and third mirrors 8 and 9
The mutual angle is called the Dach angle, and it is designed with a fairly high precision so that it is exactly 90 °.

FIG. 6 shows an optical path for optical imaging when a 3-line color CCD is used as the CCD 12.
The CCD 12 is a line sensor in which a large number of pixels are arranged in a row in the lateral direction, and three pixel rows are formed in the upper, middle, and lower sides, and R (red), G (green), and B (blue) are arranged from the top. About 0.
They are lined up at intervals of 1 mm. Therefore, on the document surface, the reading positions are different for each color of R, G, and B at the same time, R is reading first, and G and B are following. The reading position of R, G, B on the document surface is about 0.5 mm when the reduction ratio of the optical system is 0.22.

What is particularly important in the optical system using the 3-line color CCD is the stability of the illuminance distribution in the sub-scanning direction (the moving direction of the scanners 5 and 10) at the reading position on the document surface. FIG. 7 shows a detailed view of the document surface and the illumination optical system portion. The R, G, and B reading lines and the illuminance distribution curve A are shown in the upper part of the figure, and the flat portion of the illuminance distribution curve A is set to be sufficiently wider than the interval between the reading lines.

By the way, regarding the roof angles of the second and third mirrors 8 and 9, it is difficult to accurately obtain 90 ° even with high accuracy, and there is a tolerance of ± 1 ° or less. Then, as shown in FIG. 7, the first and second scanners 5, 10 are connected.
While moving and reading the image of the document, CCD
On 12, the image pickup position moves up and down. In other words, when viewed from the R, G, and B lines of the same CCD 12, the reading position on the document surface is displaced. If this deviation is large, various problems occur. One of them is uneven reading density depending on the position on the document surface.

For example, if the roof angle has a tolerance of 0.5 degrees,
The reading position on the document surface deviates by about 0.7 mm between the start side and the end side of sub-scanning (reading). Then, since the relationship between the reading line and the illuminance distribution curve A in FIG. 7 shifts to the left and right, for example, the center of the flat portion of the illuminance distribution curve A is the center line of the CCD 12 adjusted by the sub-scanning start side. Even if it is aligned with the G line, the reading position of either R or B deviates from the flat part of the illuminance distribution curve A, because it is displaced by 0.7 mm to the left or right on the sub-scanning end side.
It approaches the inclined part. This is called the optical axis shift. Generally, the optical axis is adjusted on the starting side of the sub-scanning and the white reference is adjusted. Therefore, if the roof angle is larger than 90 °, the optical axis is adjusted on the ending side of the sub-scanning. The center shifts to the B side, the read value of B becomes large and R becomes small, and conversely, when the roof angle is smaller than 90 °, the center of the optical axis shifts to the R side and the read value of B becomes small and R becomes large.

Further, while the first and second scanners 5 and 10 are moving in the sub-scanning direction, the optical axis of the reading position is simultaneously displaced with respect to the CCD 12, which is the reading sensor.
Seen from 12, the speed of optical imaging changes. This appears as a magnification error in the sub-scanning direction. That is, if the optical axis moves downward, the magnification increases,
Conversely, if you move up, the magnification will be smaller. For example, when a straight line with a length of 100 mm is read in the sub-scanning direction, CC
When the optical axis is vertically displaced by 0.1 mm on D12, the magnification error in the sub-scanning direction becomes 0.5%. Therefore, the present invention corrects the optical axis shift of such an optical system to eliminate the magnification error due to the optical axis shift.

Next, a specific example of the configuration of the present invention will be described. 2 is a block diagram of an electric circuit for detecting the amount of optical axis deviation, and FIGS. 1, 3 and 4 are diagrams of a mechanism for correcting the optical axis deviation during image reading. First, the electric circuit of FIG. 2 will be described. This electric circuit is an A / D that converts the analog image signal from the CCD 12 into a digital signal.
A converter 36, a memory 37 for storing output values of R, G, B colors in the image signal converted into a digital signal,
It is composed of an arithmetic circuit 38 connected to the memory 37. Is this electric circuit provided in the document reader?
Or it is installed outside as a jig.

The above electric circuit operates as follows. First, an achromatic chart with a uniform density or a plurality of patches is placed on the document surface, and this is read to read R, G, and
The output value of each color B is stored in the memory 37. If there is no deviation of the optical axis, it is an achromatic color, so the output value should be the same for each color. The arithmetic circuit 38 calculates the optical axis deviation amount from the output ratio of each color. As mentioned above, R, G, B
If at least the direction of the deviation is known from the magnitude relationship of the output values of the respective colors, and in addition the relationship between the ratio of each color and the deviation amount is known, the optical axis deviation amount can be immediately detected.
Regardless of whether the roof angles of the second and third mirrors 8 and 9 are larger or smaller than 90 °, the amount of deviation of the optical axis is roughly proportional to the position in the sub-scanning direction. For example, if the amount of deviation from a position 100 mm from the home position is 0.1 mm, it will be 0.2 mm at a position 200 mm. In this way, the shift amount with respect to the position in the sub-scanning direction can be known.

FIG. 1 shows an example of a mechanism for moving the printed board 30 on which the CCD 12 is mounted up and down with respect to the optical axis to correct the optical axis shift. The printed circuit board 30 is vertically and vertically movably held by a pair of guide rails 33 sandwiching both left and right edge portions in FIG. On the left and right sides of the lower side of the printed circuit board 30, a pair of springs 3 are connected to each other on one side.
The printed circuit board 30 is always urged toward the base side (lower side in FIG. 1) by connecting the two. A pair of holes 30 is provided on the left and right of the upper side of the printed circuit board 30.
a and 30a are opened, and the tips of the arrow-shaped pins 29 and 29 corresponding to the arrowheads of the arrow-shaped pins 29 and 30a are initially inserted about half. The pins 29, 29 are provided so as to be movable back and forth in the longitudinal direction from the direction perpendicular to the surface of the printed circuit board 30, and the tip portions thereof are provided with the holes 30a, 3
The printed circuit board 30 moves up and down depending on how much it is put in and taken out of the 0a. The guide rails 33 and 33 are provided so that the printed circuit board 30 does not move in the front-rear direction due to the forward and backward movement of the pins 29 and 29.

3 and 4 show an example of a drive system for inserting and removing the pins 29, 29. In FIG. 3, the reading drive source that relatively moves the reading position on the document surface, that is, the drive motor 20 of the first and second scanners 5 and 10 is set to the pin 2
An example in which 9 and 29 are moved forward and backward to be used as a drive source of a correction means for correcting the relative displacement between the optical axis and the CCD 12 will be shown. In FIG. 3, the rotational force of the motor 20 as the reading drive source is transmitted to the shaft 21 in which the pair of drums 22 and 22 are integrally provided at both ends. One end of each wire 25, 25 is fixed to each of the drums 22, 22, and the drums 22 and 22 are wound appropriately. The wires 25, 25 are respectively hooked on the pulleys 23, 23 and folded back, and then hooked on the pulleys 24, 24 attached to the second scanner 10, respectively, and folded back. It is fixed to the immovable part such as. Each wire 25, 25
Is integrally connected to both ends of the first scanner 5 between the pulleys 23 and 24. Pulley 2 of the second scanner 10
Another pulley provided coaxially with 4, 24 (not shown)
Another wire 26, 26 is hung on each wire 26,
One end of 26 is fixed to the drums 22 and 22, and the other ends of the wires 26 and 26 are fixed to the non-moving part via tension springs. As a result, the second scanner 10 and the first scanner 5 via the wires 25, 25 are urged to move in one direction.

The rotational force of the motor 20 is also transmitted to the speed reducer 27 whose speed reduction ratio can be varied. The speed reducer 27 has two output shafts, and each output shaft has a worm gear 28, 28.
Are attached or formed. On the other hand, the pin 2
Worm gears having the same pitch as the worm gears 28, 28 with the same pitch as the worm gears 28, 28 are attached or formed on the reflection side (rear end portion) of the arrow-shaped tip end portions 9 and 29, and both worm gears mesh with each other.

The above-mentioned first scanner 5 and second scanner 1
The moving mechanism itself of 0 is well-known, and the wires 25, 25 are wound around the drums 22, 22 by the forward and reverse rotation of the motor 20 or are fed out from the drums 22, 22 by the above-mentioned urging force. The first scanner 5 moves by the same distance as, and the second scanner 10 moves in the same direction by a distance half the moving distance of the first scanner 5. Further, since the rotational force of the motor 20 is also transmitted to the pins 28, 28 via the speed reducer 27, the worm gears 28, 28 are rotationally driven in synchronism with the movements of the first and second scanners 5, 10. 29, 29 are moved forward and backward. Pin 2
The printed circuit board 30 is pushed up and down by its arrow-shaped tip portion by the forward and backward movement of 9, 29.
It is possible to correct the displacement of the CCD attached to 0 with respect to the optical axis.

The reduction ratio of the decelerator 27 can be varied by calculating the detected optical axis deviation amount or deviation speed. For example, when a deviation of 0.1 mm is detected with respect to 100 mm in the sub-scanning direction, the reading speed of the scanner and the optical axis deviation speed become 1/1000. Therefore, the reduction ratio is the arrow pin 2
It may be set to be 1/1000 including the sizes of the arrowhead-shaped tip portions 9 and 29. If only the direction of the deviation can be known by detecting the deviation of the optical axis, the reduction ratio can be changed in small steps so that the output values of the respective colors are the same. The speed reduction ratio may be a negative value. As a result, the pins 29, 29 can be rotated in the opposite direction to the rotation direction of the motor 20.

If the tolerances of the roof angles of the second and third mirrors 8 and 9 constituting the first scanner 5 are different between the left and right of these mirrors 8 and 9 or the frame of the device is bent, the optical axis is changed. The amount of misalignment is not always proportional to the position, but varies depending on the top, bottom, left, and right of the document surface, which is unpredictable. In such a case, the reading drive source is not shared as the drive source of the correction unit, but instead of FIG.
The correction means may be driven by a separately provided drive source as in the embodiment shown in FIG. This is the first,
The drive mechanism of the second scanners 5 and 10 is configured in the same manner as the embodiment of FIG. 3, and a pair of motors 31 and 31 as drive sources of correction means are provided separately from the drive mechanisms of the scanners 5 and 10.
The left and right pins are provided independently of each other, and the pair of left and right pins 29, 29 are moved forward and backward by the rotation of the worm gears 28, 28 provided on the output shafts of the respective motors 31, 31, so that the left and right heights of the printed circuit board 30 integrally including the CCD 12 are adjusted. It is designed to be controlled independently. According to the embodiment shown in FIG. 4, C
The left and right imbalance of the CD 12 can also be corrected.

As a method of detecting the optical axis shift amount, a magnification error in the sub-scanning direction may be used instead of using the RGB output values as described above. For example, a large number of straight lines of a certain length (for example, 100 mm) extending in the sub-scanning direction are prepared on the document surface, read, and the number of the lines is calculated to calculate the magnification error. From this calculated value, the amount of optical axis deviation depending on the location is predicted.

The timing of detecting the amount of optical axis deviation is determined, for example, by using a dedicated chart at the time of adjustment on the manufacturing line, and the image data of each place is stored in the memory and the arithmetic circuit provided outside the document reading device. Calculate the amount of axis deviation. This is stored in, for example, the memory of the system controller in the apparatus, and the deviation amount is corrected all the time after the product is shipped. The system controller memory stores various adjustment values and is not specifically provided for this purpose.

However, this cannot cope with changes over time and changes due to temperature and humidity. So under the user,
A dedicated touch key may be provided so that the correction of the optical axis deviation can be performed at any time by the service person or the user, or the optical axis deviation correction may be selected in the service person mode. Further, at this time, a memory and an arithmetic circuit for storing image data at each place are provided in the apparatus. The service person or the user places a dedicated chart on the document surface to read it, and updates the deviation amount at each place. This allows the latest and most appropriate correction.

However, it is difficult for a service person or user to prepare a dedicated chart. It is difficult to store, and it takes time to prepare and place it on the original. Therefore, as shown in FIG. 9, an image readable range 1
6, patches P1, P2, ... P8 for detecting the deviation amount are installed in advance at appropriate plural positions outside the document placing area 15, and when the optical axis deviation correction is selected, these patches P
1, P2, ... P8 images are read. CCD
Since the image readable range 16 by 12 is generally larger than the document placing area 15 by about 5 mm at each of the four corners, the image readable area 16 is not the original placing area 15 and the document placing area 15 is larger.
The outer part is used. In addition, by doing so, it is possible to correct the optical axis deviation every certain period of time, even when the service person or the user does not make a particular selection, and it is also possible to do so every time the document is read. It is also possible to perform the scan on the sheet and correct the optical axis deviation in real time during the reading.

The optical axis deviation correction mechanism shown in FIGS. 1, 3, and 4 is merely an example. For example, eccentric pins are used instead of the arrow-head type pins 29, 29. By adjusting the rotational position, the vertical position of the reading sensor can be adjusted to correct the optical axis shift, or other appropriate mechanism can be adopted. In addition, it goes without saying that the design can be arbitrarily changed within the technical scope described in the claims.

[0035]

According to the inventions of claims 1 and 3 ,
When the reading position is relatively moved, the deviation amount of the optical axis of the optical system is detected, and the optical axis and the reading sensor are moved relative to each other according to the deviation amount detected when the document is read by the reading sensor. Since the correction means for correcting the positional deviation is provided,
By relatively moving the reading sensor so as to correct the optical axis shift by the correction unit, it is possible to improve the density unevenness of the image and the magnification error. According to the invention of claim 1,
In addition, a method of correcting the detected optical axis deviation when reading a document
As the amount of optical axis deviation by synchronizing with the scanner motor
Since the reading sensor is moved at the corresponding speed,
There is no need to provide a special drive source for axis misalignment correction,
Cost reduction is possible and the optical axis is not
It becomes possible to make corrections.

According to the second aspect of the invention, when the 3-line color image sensor is used as the reading sensor, 3
Since the optical axis deviation is detected by recognizing the ratio of the output values of the lines, this allows the amount of optical axis deviation to be detected simply without using any special means, which enables cost reduction. Besides, it is possible to save the design work.

According to the fourth aspect of the invention, since the optical axis shift is detected by detecting the magnification error in the sub-scanning direction, this makes it possible to use a simple method without using special means in any document reading apparatus. Since the amount of optical axis deviation can be detected, the optical axis deviation can be detected regardless of the type and method of the document reading apparatus, and the cost can be reduced and the design labor can be saved.

[0038]

According to the fifth aspect of the present invention, since the function of detecting the amount of optical axis deviation is provided in the document reading apparatus, even if the optical axis deviation changes with time or due to environmental conditions, the user or The serviceman can arbitrarily detect the optical axis shift and update the correction data. This enables the latest and optimum optical axis correction.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of an optical axis deviation correction mechanism applicable to a document reading apparatus according to the present invention.

FIG. 2 is a block diagram showing an example of a signal processing system applicable to a document reading apparatus according to the present invention.

FIG. 3 is a plan view showing another example of an optical axis deviation correction mechanism applicable to the document reading apparatus according to the present invention.

FIG. 4 is a plan view showing still another example of the optical axis deviation correction mechanism applicable to the document reading apparatus according to the present invention.

FIG. 5 is a side view showing a general example of a document reading device.

FIG. 6 is a side view showing an example of a reading optical system in the same document reading device.

FIG. 7 is a partial cross-sectional side view showing a portion of an illumination system in the same document reading device.

FIG. 8 is a side view showing a shift of an optical axis due to movement of a reading position in the document reading apparatus.

FIG. 9 is a plan view showing an arrangement example of optical axis deviation amount detecting members applicable to the document reading apparatus according to the present invention.

[Explanation of symbols]

1 light source 3 First mirror that makes up the optical system 8 Second mirror that makes up the optical system 9 Third mirror that makes up the optical system 11 Lenses that make up the optical system 12 CCD as a reading sensor 20 Motor as a reading drive source 29 Pins as correction means 30 Motor as Driving Source of Correction Unit

Claims (5)

(57) [Claims] 1. A light source for illuminating an original surface, a reading sensor including a large number of photoelectric conversion elements for optically reading and photoelectrically converting reflected light from the original, and for guiding reflected light from the original to the reading sensor. In an original reading device that has an optical system and a reading drive source that relatively moves the reading position of the original surface by the reading sensor, detects the amount of deviation of the optical axis of the optical system when moving the reading position relatively. detection means for, when the document reading by the reading sensor, to have a correction means for correcting the deviation of the positional relationship by relatively moving the reading sensor to the optical axis in accordance with the detected the deviation amount, the correction As the driving source of the means, the reading position with respect to the original
The reading drive source that moves the
An original reading device characterized in that the movement of a driving source and the movement of a reading driving source are synchronized . 2. The document reading apparatus according to claim 1, wherein the reading sensor is a three-line color image sensor, and the magnitude of each output of the three lines is recognized in order to detect the shift amount of the optical axis. 3. A light source for illuminating the surface of a document and a reflection from the document.
A large number of photoelectric conversions that optically read the incident light and perform photoelectric conversion
The reading sensor consisting of elements and the reading light from the reflected light from the original
Sensor and the optical system to guide the
A source having a reading drive source that relatively moves the reading position
In the draft reading device, the reading position of the document surface by the reading sensor is relatively moved.
Detecting means for detecting the amount of deviation of the optical axis of the optical system
And the amount of deviation detected when the document is read by the reading sensor.
The optical axis and the reading sensor are moved relative to each other according to
A correction unit that corrects the misalignment, and the left and right heights of the reading sensor are used as a driving source of the correction unit.
It has a pair of motors that independently control
Document reading apparatus according to symptoms. 4. The detecting means detects the magnification error in the moving direction.
Claim 1, characterized in that for detecting the amount of deviation of the optical axis Te or
Or the document reading device described in 3 . 5. The document reading apparatus according to claim 1, further comprising detection means for detecting a deviation amount of the optical axis in the apparatus.