Patent Publication Number: US-2022229182-A1

Title: Surveying Instrument

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a surveying instrument having functions of a total station or a laser scanner. 
     As surveying instruments, there are total stations which enable the prism distance measurement or non-prism distance measurement or laser scanners which perform the distance measurement while scanning an object. In these surveying instruments, to determine a position of a surveying instrument main body, the sighting in a reference direction, or a reference point or a measuring point using a reflecting object such as a retro-reflector must be highly accurately measured. For this reason, the sighting using the telescope (narrow-angle) or the detection of the reflecting object is required. 
     In a general total station having a telescope, a highly-accurate rotating shaft is required. Therefore, a size and a weight of the surveying instrument main body increase. Further, in the conventional total station, for the sighting or the detection of the reflecting object, the main body itself must be directed toward an object, and the rapid measurement cannot be performed. On the other hand, since the laser scanner does not have a function for the sighting using the telescope (narrow-angle) or the detection of the reflecting object, a reference direction, a reference point, or a measuring point cannot be highly accurately measured. 
     SUMMARY OF INVENTION 
     It is an object of the present invention to provide a surveying instrument which enables rapidly performing the highly accurate measurement. 
     To attain the object as described, a surveying instrument according to the present invention is configured to include a distance measuring light projecting module configured to project a distance measuring light along a distance measuring optical axis, a light receiving module configured to receive a reflected distance measuring light, a distance measurement arithmetic module configured to measure a distance to an object and the reflection intensity of the reflected distance measuring light based on a transmission signal of the distance measuring light and a light reception signal of the reflected distance measuring light, a narrow-angle image pickup module configured to have a narrow-angle image pickup optical axis partially shared with the distance measuring optical axis and acquire an image with the distance measuring optical axis as a center, an optical axis deflector configured to have a wavelength dispersion compensation prism arranged in a shared portion of the distance measuring optical axis and the narrow-angle image pickup optical axis and a rotating shaft vertical or substantially vertical with respect to incidence/projection end faces of the wavelength dispersion compensation prism and deflect the distance measuring optical axis by the rotation of the wavelength dispersion compensation prism, an extracting means configured to extract an end face reflection image of the wavelength dispersion compensation prism from the image, and an arithmetic control module configured to control the optical axis deflector and the distance measurement arithmetic module and calculate a deflecting direction of the optical axis deflector based on the end face reflection image extracted by the extracting means. 
     Further, in the surveying instrument according to a preferred embodiment, a detecting light projecting module configured to project a detecting light for detecting the object along a detecting light optical axis, wherein the detecting light optical axis is partially shared with the distance measuring optical axis and the narrow-angle image pickup optical axis, the wavelength dispersion compensation prism is arranged in a shared portion of the respective axes, and the extracting means is configured to extract at least one of the distance measuring light and the detecting light reflected on an end face of the wavelength dispersion compensation prism from the image. 
     Further, in the surveying instrument according to a preferred embodiment, at least one of the distance measuring light and the detecting light is configured to enter the end face of the wavelength dispersion compensation prism at a tilt with respect to the rotating shaft. 
     Further, in the surveying instrument according to a preferred embodiment, a wide-angle image pickup module configured to have an angle of view substantially equal to a maximum deflection range of the optical axis deflector. 
     Further, in the surveying instrument according to a preferred embodiment, an attitude detector configured to detect a tilt with respect to the horizontality, wherein the arithmetic control module is configured to correct a measurement result based on a detection result of the attitude detector. 
     Furthermore, in the surveying instrument according to a preferred embodiment, the arithmetic control module is configured to enable identifying an object reflection image reflected on the object and the end face reflection image based on the reflection intensity. 
     According to the present invention, a surveying instrument is configured to include a distance measuring light projecting module configured to project a distance measuring light along a distance measuring optical axis, a light receiving module configured to receive a reflected distance measuring light, a distance measurement arithmetic module configured to measure a distance to an object and the reflection intensity of the reflected distance measuring light based on a transmission signal of the distance measuring light and a light reception signal of the reflected distance measuring light, a narrow-angle image pickup module configured to have a narrow-angle image pickup optical axis partially shared with the distance measuring optical axis and acquire an image with the distance measuring optical axis as a center, an optical axis deflector configured to have a wavelength dispersion compensation prism arranged in a shared portion of the distance measuring optical axis and the narrow-angle image pickup optical axis and a rotating shaft vertical or substantially vertical with respect to incidence/projection end faces of the wavelength dispersion compensation prism and deflect the distance measuring optical axis by the rotation of the wavelength dispersion compensation prism, an extracting means configured to extract an end face reflection image of the wavelength dispersion compensation prism from the image, and an arithmetic control module configured to control the optical axis deflector and the distance measurement arithmetic module and calculate a deflecting direction of the optical axis deflector based on the end face reflection image extracted by the extracting means. As a result, the optical axis deflection is performed by the wavelength dispersion compensation prism, the rapid optical axis deflection is enabled performed by the small inertial force of the rotating portions, the magnification and distortions of the image can be corrected, an influence of fluctuations of the wavelength dispersion compensation prism can be removed, and the highly accurate measurement can be realized. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic block diagram of a surveying instrument. 
         FIG. 2  is a side elevation view of an optical axis deflector in the surveying instrument. 
         FIG. 3A  is a perspective view of the optical axis deflector, and  FIG. 3B  is a primary part enlarged view of wavelength dispersion compensation prisms. 
         FIG. 4  is a graph to show a relationship of wavelengths and errors between the wavelength dispersion compensation prism in a first embodiment and a normal optical prism. 
         FIG. 5  is an explanatory drawing to explain a relationship between deflecting directions and a synthetic deflecting direction of respective disk prisms. 
         FIG. 6A  shows a narrow-angle image with no change in magnification in a “Y” axis direction,  FIG. 6B  shows a narrow-angle image with a change in magnification in the “Y” axis direction, and  FIG. 6C  shows a distorted narrow-angle image with a change in magnification in a rotating direction. 
         FIG. 7  is a graph showing angular differences “θ” of the respective disk prisms and changes in magnification in the “Y” axis direction. 
         FIG. 8A  is an explanatory drawing to show fluctuating directions of the wavelength dispersion compensation prisms, and  FIG. 8B  is an explanatory drawing to show a change in deflecting directions due to fluctuations of the wavelength dispersion compensation prisms. 
         FIG. 9A  is an explanatory drawing to explain the end face reflections when the angular difference “θ”=180°,  FIG. 9B  is an explanatory drawing to explain the end face reflections when the angular difference “θ”=0°,  FIG. 9C  shows a narrow-angle image in a state of  FIG. 9A , and  FIG. 9D  is an explanatory drawing to show a change in end face reflection image when the wavelength dispersion compensation prisms are rotated. 
         FIGS. 10A-10C  show wavelength dispersion compensation prisms and narrow-angle images according to a second embodiment of the present invention, where  FIG. 10A  is an explanatory drawing to explain the end face reflections when an angular difference “θ”=180°,  FIG. 10B  shows a narrow-angle image in a state of  FIG. 10A , and  FIG. 10C  is an explanatory drawing to show a change in end face reflection image when the wavelength dispersion compensation prisms are rotated. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A description will be given below on embodiments of the present invention by referring to the attached drawings. 
     A description will be given on a surveying instrument according to a first embodiment of the present invention by referring to  FIG. 1  to  FIG. 3   
     A surveying instrument  1  mainly includes a distance measuring light projecting module  11 , a light receiving module  12 , a detecting light projecting module  13 , a wide-angle image pickup module  14 , a narrow-angle image pickup module  71 , a distance measurement arithmetic module  15 , an arithmetic control module  16 , a storage module  17 , an attitude detector  18 , a projecting direction detector  19 , a motor driver  21 , a wide angle image pickup control module  23 , an image processor  24 , a display module  25 , an optical axis deflector  26 , and a narrow angle image pickup control module  27 . They are accommodated and integrated in a casing  29 . It is to be noted that the distance measuring light projecting module  11 , the light receiving module  12 , the distance measurement arithmetic module  15 , the optical axis deflector  26  and the like constitute a distance measuring module  28  having functions as an electronic distance meter. 
     As each of the distance measurement arithmetic module  15  and the arithmetic control module  16 , a CPU specialized for the present embodiment, a general-purpose CPU, an embedded CPU, a microprocessor, or the like is used. Further, as the storage module  17 , a semiconductor memory such as a RAM, a ROM or a Flash ROM, a magnetic recording memory such as an HDD, or an optical recording memory such as a CDROM is used. 
     The storage module  17  stores various types of programs for carrying out the present embodiment, and the distance measurement arithmetic module  15  and the arithmetic control module  16  expand and execute the stored programs, respectively. Further, in the storage module  17 , various types of data, for instance, the measurement data or the image data are stored. 
     The arithmetic control module  16  controls the optical axis deflector  26  via the motor driver  21 , and controls the deflection of a distance measuring optical axis  39  (to be described later). Further, the arithmetic control module  16  performs the integration control of the distance measurement arithmetic module  15 , the wide angle image pickup control module  23 , and the narrow angle image pickup control module  27 , and the synchronous control of the distance measurement, the imaging, the detection of a retro-reflective detecting light. Further, the arithmetic control module  16  performs the cooperative processing (to be described later) with the image processor  24 , the precise deflecting direction calculation processing for the distance measuring optical axis  39  based on a detection result of the projecting direction detector  19 , the vertical angle and three-dimensional coordinate calculation processing for a measuring point based on a detection result of the attitude detector  18 , and the like. 
     The attitude detector  18  detects a tilt angle with respect to the horizontality or the verticality of the surveying instrument  1 , and a detection result is input to the arithmetic control module  16 . Further, as the attitude detector  18 , a tilt detector such as a tilt sensor is used, and an attitude detection device disclosed in Japanese Patent Application Publication No. 2016-151423 can be used. 
     The distance measuring light projecting module  11  has a projecting optical axis  31 , as well as a light emitter  32  and a light projecting lens  33  provided on the projecting optical axis  31 . The light emitter  32  is, for instance, a laser diode (LD) which emits an infrared light or a near-infrared light as a distance measuring light  37 , and the light projecting lens  33  turns the distance measuring light  37  into a parallel light flux. Further, the projecting optical axis  31  is deflected by a beam splitter  34  as a deflection optical member provided on the projecting optical axis  31  and a reflecting mirror  36  as a deflection optical member provided on a light receiving optical axis  35  so that the projecting axis  31  coincides with the light receiving optical axis  35 . The reflecting mirror  36  has a shape equivalent to or slightly larger than a light flux diameter of the distance measuring light  37 , and a size equivalent to wavelength dispersion compensation prisms  55  and  58  (to be described later). The reflecting mirror  36  and the wavelength dispersion compensation prisms  55  and  58  occupy a limited portion with the light receiving optical axis  35  as a center. 
     The beam splitter  34  is, for instance, a half-mirror or a polarization beam splitter having polarization optical characteristics. The beam splitter  34  reflects a part of the distance measuring light  37  and transmits through the remainder part. Further, the reflecting mirror  36  totally reflects the distance measuring light  37  and a detecting light  47  (to be described later). 
     The light emitter  32  pulse-emits a laser beam or burst-emits a laser beam. The distance measuring light projecting module  11  projects a pulsed laser beam (or a burst-emitted laser beam) emitted from the light emitter  32  as the distance measuring light  37 . It is to be noted that the burst light emission is disclosed in Japanese Patent Application Publication No. 2016-161411. Further, by outputting a timing signal as a transmission signal for the distance measuring light, the distance measurement arithmetic module  15  has the distance measuring light projecting module  11  pulse-emitted or burst-emitted the distance measuring light  37 . 
     A description will be given on the light receiving module  12 . A reflected distance measuring light  38  from an object to be measured (an object) enters the light receiving module  12 . The light receiving module  12  has the light receiving optical axis  35 , and the projecting optical axis  31  deflected by the beam splitter  34  and the reflecting mirror  36  coincides with the light receiving optical axis  35 . 
     It is to be noted that a state where the projecting optical axis  31  coincides with the light receiving optical axis  35  is determined as the distance measuring optical axis  39 . 
     The optical axis deflector  26  has a disk prism (to be described later) and can deflect the distance measuring light  37  to an arbitrary direction by the rotation of the disk prism. The disk prism is, for instance, a pair of disk prisms  53  and  54  (to be described later), and the wavelength dispersion compensation prisms  55  and  58  are provided in central portions of the disk prisms  53  and  54 . The optical axis deflector  26  is arranged on a deflection reference optical axis “O”. Further, the optical axis deflector  26  is configured in such a manner that incidence end faces and projection end faces of the wavelength dispersion compensation prisms  55  and  58  become vertical with respect to the deflection reference optical axis “O” and the deflection reference optical axis “O” passes near a rotating shaft  52  (to be described later) of the optical axis deflector  26 . It is to be noted that the incidence end faces and the projection end faces are also referred to as incidence/projection end faces altogether. 
     As will be described later, the deflection reference optical axis “O” is an optical axis serving as a reference for the optical axis deflector  26  and has predetermined relationships with all optical axes in the surveying instrument  1  (known interaxial distances and angular relationships). Here, all optical axes refer to the distance measuring optical axis  39 , a detecting light optical axis  44  (to be described later), a wide-angle image pickup optical axis  66  (to be described later), and a narrow-angle image pickup optical axis  44 ′ (to be described later). 
     A focusing lens  41  is arranged on the light receiving optical axis  35  having passed through the optical axis deflector  26 . Further, on the light receiving optical axis  35 , a photodetector  42  is provided. The photodetector  42  is, for instance, an avalanche photodiode (APD) or an equivalent photoelectric conversion element. 
     The focusing lens  41  forms an image of the reflected distance measuring light  38  on the photodetector  42 . The focusing lens  41 , the photodetector  42  and the like constitute the light receiving module  12 . 
     The photodetector  42  receives the reflected distance measuring light  38 , and emits a light reception signal. The light reception signal is input to the distance measurement arithmetic module  15 . The distance measurement arithmetic module  15  performs the distance measurement to the object (the optical wave distance measurement) and the measurement of the reflection intensity based on a transmission signal and the light reception signal of the distance measuring light  37 . As signals for the distance measuring light  37  and the reflected distance measuring light  38 , it is possible to use various types of signals, for instance, a light emission timing signal for the distance measuring light  37  and a light reception timing signal for the reflected distance measuring light  38 , or a phase signal for the distance measuring light  37  and a phase signal for the reflected distance measuring light  38  (a phase difference signal). 
     It is to be noted that, as the measurement, a prism survey in a case where the object has the retroreflective ability, or a non-prism survey in a case where the object has no retroreflective ability is performed. In the following description, the object is a reflecting object such as a prism or a corner cube, and the prism survey with the retroreflective ability will be described. 
     A description will be given on the detecting light projecting module  13  which irradiates the detecting light  47 . Further, the detecting light projecting module  13  has the detecting light optical axis  44 , as well as a detecting light source  45 , a detecting light lens  48 , and a split mirror  49  which are arranged on the detecting light optical axis  44 . The detecting light  47  is projected from the detecting light source  45  along the detecting light optical axis  44 . The detecting light  47  is deflected by the split mirror  49  along the detecting light optical axis  44  and coincides with light projecting optical axis  31 . Therefore, the detecting light  47  is irradiated coaxially with the distance measuring light  37 . 
     Here, a spread angle of the detecting light  47  irradiated from the detecting light projecting module  13  is determined depending on a focal distance of the detecting light lens  48  and a size of the detecting light source  45 . As the spread angle of the detecting light  47 , a spread angle of approximately 1° to 2° is usually selected in accordance with requirements of a distance and an angular range of the reflecting object to be detected. Further, a wavelength of the detecting light  47  is selected so that an error due to a wavelength difference from the distance measuring light  37  (see  FIG. 4 ) is sufficiently smaller than the spread angle. 
     It is to be noted that, as the detecting light source  45 , an emission light source such as an LED (a light-emitting diode) or an LD is used. Since the optical axis deflector  26  uses the wavelength dispersion compensation prisms  55  and  58 , the wavelength of the detecting light  47  can be selected from a wavelength band of a red light to a near-infrared light, for instance, a range of 650 nm to 850 nm. For instance, a light of 850 nm is selected as the distance measuring light  37 , and a light of 650 nm is selected as the detecting light  47 . Here, if a visible light (a red color) is used as the detecting light  47 , a worker can visually confirm the detecting light  47  on the reflecting object (the object) side, and positioning the object can be made efficient. Further, as the detecting light source  45 , a light beam emitted from the LED or the LD may be led through an optical fiber so that a projection end face of the optical fiber can be adopted as the detecting light source. 
     The detecting light  47  reflected by the object enters the optical axis deflector  26  coaxially with the reflected distance measuring light  38 , and the detecting light  47  and the reflected distance measuring light  38  are transmitted through the optical axis deflector  26  and then reflected by the reflecting mirror  36 . 
     The reflecting mirror  36  separates the narrow-angle image pickup optical axis  44 ′ from the distance measuring optical axis  39 , and deflects the narrow-angle image pickup optical axis  44 ′. The beam splitter  34 , the detecting light split mirror  49 , the focusing lens  46  and a narrow-angle image pickup element  51  are arranged on the deflected narrow-angle image pickup optical axis  44 ′. 
     The distance measuring optical axis  39  is partially shared with the narrow-angle image pickup optical axis  44 ′. The detecting light split mirror  49 , the beam splitter  34 , the focusing lens  46 , the narrow-angle image pickup element  51 , and the like function as a narrow-angle image pickup module  71  which acquires an image of a measuring point portion irradiated with the distance measuring light  37 . The narrow-angle image pickup module  71  acquires a narrow-angle image in a predetermined image positional relationship (for instance, an image center) with reference to the distance measuring optical axis  39 . It is to be noted that a field angle of the narrow-angle image pickup module  71  is, for instance, approximately ±2° to ±3°, which is narrower than a field angle of the wide-angle image pickup module  14  (for instance, a deflection angle ±30°), images with high magnifications are acquired. 
     The narrow-angle image pickup element  51  images the detecting light  47  and the reflected distance measuring light  38  reflected by the retroreflective ability of the object as a part of a narrow-angle image together with the object and the background light. Further, the narrow-angle image pickup element  51  is configured to also image the detecting light  47  and the distance measuring light  37  reflected by the end face reflection and transmitted through the beam splitter  34  and the detecting light split mirror  49 , and the acquired image data is input to the narrow angle image pickup control module  27 . 
     The narrow-angle image pickup element  51  is a CCD or a CMOS sensor which is an aggregation of pixels, and a position of each pixel on the narrow-angle image pickup element  51  can be identified. For instance, each pixel has pixel coordinates in a coordinate system with the narrow-angle image pickup optical axis  44 ′ as an origin, and its position on the narrow-angle image pickup element  51  can be identified by the pixel coordinates. An image signal output from the narrow-angle image pickup element  51  has the pixel coordinate information and the image signal is input to the narrow angle image pickup control module  27 . 
     The narrow angle image pickup control module  27  can perform the timing control to turn on or off the detecting light source  45  so that a reflection image of the detecting light  47  and a reflection image of the reflected distance measuring light  38  in a narrow-angle image can be accurately detected. Further, some of functions of the arithmetic control module  16  may be allocated to the narrow angle image pickup control module  27 . 
     A light transmitted through the wavelength dispersion compensation prisms  55  and  58  (a part of a reflected detecting light and the reflected distance measuring light  38 ) can solely enter the narrow-angle image pickup element  51  so that an object reflection image (a reflection image of the distance measuring light  37  and the detecting light  47  reflected by the object) can be acquired. Further, the narrow-angle image pickup element  51  can also detect an end face reflection image of the detecting light source  45  or the light emitter  32  by the end face reflection of the wavelength dispersion compensation prisms  55  and  58 . 
     As described above, the detecting light projecting module  13 , the focusing lens  46 , the narrow-angle image pickup element  51  and the like acquire an image of a predetermined range in an irradiating direction of the distance measuring light  37  with the distance measuring optical axis  39  as a center. 
     A description will be given on particulars of the optical axis deflector  26  by referring to  FIG. 2 ,  FIG. 3A ,  FIG. 3B , and  FIG. 4 . 
     The optical axis deflector  26  is included of the pair of disk prisms  53  and  54  and motors  63  and  65  which rotate and drive the disk prisms  53  and  54 . The disk prisms  53  and  54  have the same shape which is a polygon with a circumscribed circle, respectively, and the disk prisms  53  and  54  have a common rotating shaft  52 . Further, the disk prisms  53  and  54  are concentrically oppositely arranged while becoming orthogonal to the rotating shaft  52 , and arranged in parallel at a predetermined interval. Further, the rotating shaft  52  and the deflection reference optical axis “O” are parallel or substantially parallel. The disk prism  53  is molded with the use of the optical glass, and has a plurality of prism columns arranged in parallel as a basic configuration and a wavelength dispersion compensation prism  55  arranged in a central portion. The wavelength dispersion compensation prism  55  is a composite prism formed by attaching an optical prism  55   a  and an optical prism  55   b  to each other. It is to be noted that, in the drawing, the disk prism  53  has three prism columns (for instance, rod-shaped triangular prisms, hereinafter they will be referred to as triangular prisms)  56   a ,  56   b ,  56   c.    
     Likewise, the disk prism  54  is molded with the use of the optical glass, has three prism columns (for instance, rod-shaped triangular prisms, hereinafter they will be referred to as triangular prisms)  57   a ,  57   b ,  57   c  arranged in parallel as a basic configuration, and has a wavelength dispersion compensation prism  58  arranged in a central portion. The wavelength dispersion compensation prism  58  is a composite prism formed by attaching an optical prism  58   a  and an optical prism  58   b  to each other. It is to be noted that the triangular prisms  56   a ,  56   b ,  56   c  and the triangular prisms  57   a ,  57   b ,  57   c  all have optical deflection characteristics of the same deflection angle. Further, the wavelength dispersion compensation prisms  55  and  58  are produced in such a manner that optical deflection characteristics of the wavelength dispersion compensation prisms  55  and  58  become the same as the optical deflection characteristics of the triangular prisms  56   a ,  56   b ,  56   c  and the triangular prisms  57   a ,  57   b ,  57   c.    
     The wavelength dispersion compensation prism  55  and the wavelength dispersion compensation prism  58  have the same configuration and are point-symmetrically arranged. It is to be noted that an incidence end face of the wavelength dispersion compensation prism  55  and a projection end face of the wavelength dispersion compensation prism  58  orthogonal to the rotating shaft  52  are determined as reference surfaces of the wavelength dispersion compensation prisms  55  and  58 . If the incidence end face and the projection end face are truly vertical with respect to the rotating shaft  52  and there is no fluctuation such as an axial deviation of the rotating shaft  52  or a face fall over error to the rotating shaft  52 , a normal line  56  (parallel to the rotating shaft  52 ) running through the center or the substantial center of each of the incidence end face and the projection end face is determined as a deflection optical axis “O” serving as a reference axial of the optical axis deflector  26 . Further, the size of each of the wavelength dispersion compensation prisms  55  and  58  (lengths of the triangular prisms  56   a ,  57   a  in a longitudinal direction and a width direction) is larger than a beam diameter of the distance measuring light  37 . 
     The wavelength dispersion compensation prism  55  and  58  are a distance measuring light deflector which is a first optical axis deflector through which the distance measuring light  37  is transmitted and from which the distance measuring light  37  is projected. Further, portions excluding the wavelength dispersion compensation prisms  55  and  58  (both end portions of the triangular prisms  56   a ,  57   a , the triangular prisms  56   b ,  56   c , and the triangular prisms  57   b ,  57   c ) are a reflected distance measuring light deflector which is a second optical axis deflector through which the reflected distance measuring light  38  is transmitted and which the reflected distance measuring light  38  enters. 
     The disk prisms  53  and  54  are independently arranged so that they can individually rotate around the rotating shaft  52 , respectively. By independently controlling rotating directions, rotation amounts, and rotation speeds, the disk prisms  53  and  54  causes deflecting the projecting optical axis  31  of the distance measuring light  37  as projected to an arbitrary direction, and a scan can be performed in an arbitrary pattern. Further, disk prisms  53  and  54  deflect the light receiving optical axis  35  of the reflected distance measuring light  38  as received in parallel with the projecting optical axis  31 . 
     An outer shape of each of the disk prisms  53  and  54  is a polygon with a circumscribed circle with the deflection reference optical axis “O” as a center, the spread of the reflected distance measuring light  38  is taken into consideration, and sizes of the disk prisms  53  and  54  are set so that a sufficient light amount can be acquired. 
     A ring gear  59  is fitted on an outer periphery of the disk prism  53 , and a ring gear  61  is fitted on an outer periphery of the disk prism  54 . 
     A driving gear  62  meshes with the ring gear  59 , and the driving gear  62  is fixed to an output shaft of a motor  63 . Similarly, a driving gear  64  meshes with the ring gear  61 , and the driving gear  64  is fixed to an output shaft of a motor  65 . The motors  63  and  65  are electrically connected with the motor driver  21 , respectively. 
     As the motors  63  and  65 , motors which can detect rotation angles are used. Alternatively, as the motors  63  and  65 , motors which rotating in correspondence with driving input values, for instance, pulse motors are used. Alternatively, rotation angle detectors which detect rotation amounts (rotation angles) of the motors, for instance, encoders may be used for detecting rotation amounts of the motors  63  and  65 . 
     As shown in  FIG. 3B , the wavelength dispersion compensation prism  55  is constituted by attaching the two optical prisms  55   a ,  55   b  having different wavelength characteristics (dispersion amounts, refraction indexes). The wavelength dispersion compensation prism  58  is similarly constituted by attaching the two optical prisms  58   a ,  58   b  having different wavelength characteristics. 
       FIG. 4  is a graph to show an error example with respect to wavelengths of lights, for instance, the reflected distance measuring light and the reflected detecting light in a case where the distance measuring optical axis  39  and the detecting light optical axis  44  have a deflection angle of ±30°. In  FIG. 4 , a reference numeral  77  denotes a graph to show an error when normal prisms (triangular prisms) are used, and a reference numeral  78  denotes a graph to show an error when the wavelength dispersion compensation prisms  55  and  58  are used. 
     As shown in  FIG. 4 , errors due to wavelengths in a wavelength band of 650 nm to 850 nm are reduced as characteristics of the wavelength dispersion compensation prisms  55  and  58 . Therefore, since a light amount can be increased, a less-blurred fine image can be acquired, and the precise sighting and image tracking is enabled. 
     The wide-angle image pickup module  14  has a wide-angle image pickup optical axis  66 , which is parallel to the deflection reference optical axis “O” of the surveying instrument  1 . Further, the wide-angle image pickup module  14  has an image pickup lens  67  and a wide-angle image pickup element  68  which are arranged on the wide-angle image pickup optical axis  66 . The wide-angle image pickup module  14  has a field angle which is equivalent or substantially equivalent to a maximum deflection range (for instance, a deflection angle ±30°) provided by the optical axis deflector  26 , and the wide-angle image pickup module  14  acquires the image data including the maximum deflection range. 
     The wide-angle image pickup element  68  is a CCD or a CMOS sensor which is an aggregation of pixels, and a position of each pixel on the wide-angle image pickup element  68  can be identified. An image signal output from the wide-angle image pickup element  68  has the positional information, the image signal is input to the wide angle image pickup control module  23 . 
     Therefore, a direction of an object (a measuring point) included in a wide-angle image acquired by the wide-angle image pickup module  14  can be immediately recognized on the wide-angle image with the use of pixel coordinates of the wide-angle image. Further, since the wide-angle image pickup optical axis  66  of the wide-angle image pickup module  14  and the narrow-angle image pickup optical axis  44 ′ have a known positional relationship, a wide-angle image acquired by the wide-angle image pickup module  14  can be easily associated with a narrow-angle image  73  (to be described later) acquired by the narrow-angle image pickup module  71 . That is, a direction of the narrow-angle image  73  can be easily confirmed based on the wide-angle image. 
     The distance measurement arithmetic module  15  controls the light emitter  32  so that the light emitter  32  pulse-emits or burst-emits (intermittently emits) a laser beam as the distance measuring light  37 . The projecting optical axis  31  is deflected by the wavelength dispersion compensation prisms  55  and  58  (the distance measuring light deflector) so that the distance measuring light  37  is directed to an object specified based on the wide-angle image or the narrow-angle image  73 . Thereby, the distance measuring optical axis  39  sights the object. 
     The reflected distance measuring light  38  reflected by the object enters via the triangular prisms  56   a ,  56   b ,  56   c , the triangular prisms  57   a ,  57   b ,  57   c  (the reflected distance measuring light deflector), and the focusing lens  41 , and the reflected distance measuring light  38  is received by the photodetector  42 . Further, in the reflected distance measuring light  38 , the reflected distance measuring light  38  transmitted through the wavelength dispersion compensation prisms  55  and  58  is reflected by the reflecting mirror  36 , and enters the narrow-angle image pickup element  51  via the focusing lens  46 . 
     It is to be noted that, if the object is a prism (the prism measurement), the reflected distance measuring light  38  retro-reflected by the prism is received by the photodetector  42 . Further, if the object is not a prism (the non-prism measurement), the reflected distance measuring light  38  naturally reflected by the object is received by the photodetector  42 . The photodetector  42  transmits a light reception signal to the distance measurement arithmetic module  15 . The distance measurement arithmetic module  15  performs the distance measurement of a measuring point (a point irradiated with the distance measuring light) in accordance with each pulsed light based on the light reception signal from the photodetector  42 . The distance measurement data is stored in the storage module  17 . 
     The projecting direction detector  19  counts driving pulses input to the motors  63  and  65 , and detects rotation angles of the motors  63  and  65 . Alternatively, based on signals from the encoders, the projecting direction detector  19  detects the rotation angles of the motors  63  and  65 , and calculates a deflection angle of the distance measuring light  37  with reference to the deflection reference optical axis “O”. 
     The wide angle image pickup control module  23  controls the imaging of the wide-angle image pickup module  14 . The wide angle image pickup control module  23  synchronizes a timing for acquiring images (a still image and a video image) by the wide-angle image pickup module  14  with a timing for performing the distance measurement using the surveying instrument  1 . Further, in a case of acquiring images by the narrow-angle image pickup module  71 , the timing for acquiring images by the narrow-angle image pickup module  71  is synchronized with the timing for the distance measurement. 
     The image processor  24  is configured to process the wide-angle image and the narrow-angle image  73  in cooperation with the arithmetic control module  16 . For the image data acquired by the wide-angle image pickup module  14  and the narrow-angle image pickup module  71 , the image processor  24  extracts a retro-reflected object reflection image and end face reflection images of the wavelength dispersion compensation prisms  55  and  58  from images. That is, the image processor  24  also functions as an extracting means for extracting end face reflection images of the wavelength dispersion compensation prisms  55  and  58  from the narrow-angle image  73 . It is to be noted that whether an extracted reflection image is an image reflected by the object or an image reflected on the end face of one of the wavelength dispersion compensation prisms  55  and  58  can be determined with the use of, for instance, the light reflection intensity with respect to the narrow-angle image pickup module  71 . 
     Further, the image processor  24  performs the correction processing for magnifications or distortions corresponding to an angular difference “Θ” of a synthetic deflection “C” and a rotation “ω”, as well as the feature point extraction, the edge extraction processing in images, the image matching processing, and the like. Here, the angular difference “Θ” represents a relative rotation angle between the disk prisms  53  and  54 , and the rotation “ω” represents a rotation angle when the disk prism  53  and  54  are integrally rotated. 
     Further, the image processor  24  calculates a positional deviation a center of the narrow-angle image  73  and the object reflection image in the narrow-angle image  73 , and outputs the positional deviation to the arithmetic control module  16 . The arithmetic control module  16  controls the optical axis deflector  26  based on a positional deviation in such a manner that the center of the narrow-angle image  73  coincides with the object reflection image, the arithmetic control module  16  enables tracking the object. 
     The display module  25  displays a wide-angle image acquired by the wide-angle image pickup module  14  and the narrow-angle image  73  acquired by the narrow-angle image pickup module  71 . As a method for displaying the wide-angle image and the narrow-angle image  73 , the display is performed using split screens. Alternatively, the wide-angle image and the narrow-angle image  73  are changed over and displayed, for instance. Further, the wide-angle image or the narrow-angle image  73  can be displayed with a scan locus superimposed. 
     A deflecting operation and a scan operation of the optical axis deflector  26  will now be described by referring to  FIG. 2 ,  FIG. 3  and  FIG. 5 . 
       FIG. 2  shows a state where the triangular prisms  56   a ,  56   b ,  56   c  and the triangular prisms  57   a ,  57   b ,  57   c  are placed in the same direction, and a maximum deflection angle (for instance, ±30°) can be acquired in this state. Further,  FIG. 3A  shows a state where any one of the disk prisms  53  and  54  is at a position rotated 180°. In this state, mutual optical operations of the disk prisms  53  and  54  are offset, and a minimum deflection angle (0°) is acquired. 
     The distance measuring light  37  is emitted from the light emitter  32 . The distance measuring light  37  is turned to a parallel light flux by the light projecting lens  33 , transmitted through the distance measuring light deflector (the wavelength dispersion compensation prisms  55  and  58 ), and projected toward the object. Here, by being transmitted through the distance measuring light deflector, the distance measuring light  37  is deflected in a necessary direction by the wavelength dispersion compensation prisms  55  and  58 . 
     The reflected distance measuring light  38  reflected by the object is transmitted through the reflected distance measuring light deflector, enters, and condensed on the photodetector  42  by the focusing lens  41 . 
     When the reflected distance measuring light  38  is transmitted through the reflected distance measuring light deflector, an optical axis of the reflected distance measuring light  38  is deflected by the triangular prisms  56   a ,  56   b ,  56   c  and the triangular prisms  57   a ,  57   b ,  57   c  so that the optical axis of the reflected distance measuring light  38  coincides with the light receiving optical axis  35 . 
       FIG. 5  shows a case where the disk prism  53  and the disk prism  54  are relatively rotated. By assuming that a deflecting direction of an optical axis deflected by the disk prism  53  is a deflection “A” and a deflecting direction deflected by the disk prism  54  is a deflection “B”, the deflections of the optical axis provided by the disk prisms  53  and  54  become a synthetic deflection “C” as an angular difference “8” between the disk prisms  53  and  54 . It is to be noted that, in the present embodiment, the arrangement of the disk prisms  53  and  54  shown in  FIG. 2  (the arrangement realizing a maximum deflection angle) has the angular difference “Θ”=0°. 
     Since the narrow-angle image pickup module  71  acquires an image of an irradiation point of the distance measuring light  37 , the narrow-angle image pickup module  71  functions as a finder for a distance measurement portion. Further, since an image acquired by the narrow-angle image pickup module  71  is acquired by the reflected distance measuring light  38  transmitted through the wavelength dispersion compensation prisms  55  and  58 , the dispersion of the wavelength is compensated, and a less-blurred fine image is acquired. 
     Here, in a case where a “y” axis direction of the narrow-angle image  73  acquired by the narrow-angle image pickup module  71  coincides with a synthetic deflection “C” direction (when the rotation “ω”=0), a magnification in the “Y” axis direction changes in correspondence with the magnitude of the angular difference “θ” between the disk prism  53  and the disk prism  54 . 
       FIG. 6A  to  FIG. 6C  show a relationship between the narrow-angle image  73  and the synthetic deflection “C”. It is to be noted that  FIG. 6A  shows a case where the magnification in the “Y” axis direction of the narrow-angle image  73  is not changed when directions of the deflection “A” and the deflection “B” are reversed and cancelled out each other and the synthetic deflection “C”=“A”+“B”=0 (the angular difference “θ”=180°) is achieved.  FIG. 6B  shows a case where the magnification in the “Y” axis direction of the narrow-angle image  73  changes and shrinks in the “Y” axis direction when the synthetic deflection “C”=“A”+“B” (the angular difference “θ”=0°) is achieved.  FIG. 6C  shows a case where the synthetic deflection “C”=“A”+“B” (the angular difference “Θ”=0°) is achieved and the deflecting direction has rotated 45° with respect to the “Y” axis direction (the rotation “ω”=45°). In this case, the narrow-angle image  73  is reduced (distorted) in a direction of the 45° rotation. 
     Further,  FIG. 6A  to  FIG. 6C  show a case where a center of the narrow-angle image  73  (an intersection of cross-hairs  74  in the drawings) is arranged so that the narrow-angle image  73  coincides with the deflection reference optical axis “O”. The center of the narrow-angle image  73  at this time is a projecting direction when a projected light projected along the deflection reference optical axis “O” is deflected by the optical axis deflector  26 . 
     Further,  FIG. 7  is a graph to show a relationship between the angular difference “θ” between the disk prism  53  and the disk prism  54  and a change in magnification in the “Y” axis direction when the “Y” axis direction of the narrow-angle image  73  has been arranged so that the narrow-angle image  73  coincides with the synthetic deflection “C” (when the entire rotation angle “ω”=0). As shown in  FIG. 7 , the magnification in the “Y” axis direction of the narrow-angle image  73  changes in correspondence with the magnitude of the synthetic deflection “C” provided by the angular difference “Θ”. The relationship between the angular difference “θ” and the magnification in the “Y” axis direction can be calculated with the use of a wavelength dispersion compensation prism constant (a refraction index, a prism angle, and the like), the synthetic deflection “C”, and the rotation co, and can be known in advance by, for instance, performing the actual measurement. Therefore, the angular difference “θ” (see  FIG. 5 ) can be acquired based on a detection result of the projecting direction detector  19 , the magnification can be corrected, and the narrow-angle image  73  can be restored to its original image. It is to be noted that a reference angle of the angular difference “Θ” between the disk prism  53  and the disk prism  54  can be arbitrarily set, and the reference angle can be, for instance, 0° (a large change in magnification) or 180° (no change in magnification due to the cancelling of the optical operation). 
     Here, if the deflection “A” and the deflection “B” have a fluctuation or a face tangle error, the synthetic deflection “C” changes in correspondence with the fluctuation.  FIG. 8A  and  FIG. 8B  are views emphatically to show an influence of an end face fluctuation of the optical axis deflector  26 . 
     A deflecting direction provided by the optical axis deflector  26  is determined based on the incidence end face of the wavelength dispersion compensation prism  55  and the projection end face of the wavelength dispersion compensation prism  58  as reference surfaces. Further, the normal line  56  of the reference surfaces coincides or substantially coincides with the rotating shaft  52 . 
     As shown in  FIG. 8A , when the wavelength dispersion compensation prism  55  fluctuates ϕz1 around the longitudinal axis and ϕy1 around the lateral axis and the wavelength dispersion compensation prism  58  fluctuates ϕz2 around the longitudinal axis and ϕy2 around the lateral axis, the deflection “A” and the deflection “B” fluctuate and the synthetic deflection “C” fluctuates as shown in  FIG. 8B . The fluctuations of ϕy1 and ϕy2 mainly cause changes in magnitude components of the deflections “A” and “B”, and the fluctuations of ϕz1 and ϕz2 mainly cause changes in rotation components of the deflections “A” and “B”. 
     The fluctuations of the deflections “A” and “B” with respect to the fluctuations of the wavelength dispersion compensation prisms  55  and  58  are determined by a wavelength dispersion compensation constant (a refraction index, a prism angle, and the like) and an incidence angle of a light beam, and the fluctuations of the deflections “A” and “B” can be calculated by the arithmetic control module  16 . Further, optical characteristics of the wavelength dispersion compensation prisms  55  and  58  provided by the measurement can be also acquired. 
     Therefore, the deflection of the synthetic deflection “C” can be accurately calculated by calculating a fluctuation of the incidence end face of the wavelength dispersion compensation prism  55  and a fluctuation of the projection end face of the wavelength dispersion compensation prism  58  with respect to the rotating shaft  52  of the optical axis deflector  26 . 
     By referring to  FIG. 9A  to  FIG. 9D , particulars of the detection of the fluctuation of the incidence end face of the wavelength dispersion compensation prism  55  and the fluctuation of the projection end face of the wavelength dispersion compensation prism  58  will now be described. 
     In the present embodiment, the fluctuation of the incidence end face of the wavelength dispersion compensation prism  55  and the fluctuation of the projection end face of the wavelength dispersion compensation prism  58  are obtained with the use of the narrow-angle image  73  for the image tracking. 
       FIG. 9A  to  FIG. 9D  are views showing a relationship between the end face reflection of the wavelength dispersion compensation prisms  55  and  58  and the narrow-angle image  73 .  FIG. 9A  shows a reflected light r 1  of the incidence end face and a reflected light r 2  of the projection end face with respect to a projecting light in a case where the angular difference “Θ” is 180° (a magnification: 1).  FIG. 9B  shows the reflected light r 1  of the incidence end face and the reflected light r 2  of the projection end face with respect to the projecting light in a case where the angular difference “Θ” is 0°. Further,  FIG. 9C  shows the narrow-angle image  73  in a case where the angular difference “Θ” is 180°. It is to be noted that, in  FIG. 9C  and  FIG. 9D , a background image is not shown. It is to be noted that, in  FIG. 9C  and  FIG. 9D , reflected lights of a detecting light “T” and a distance measuring light “M” on the incidence end face are Tr 1  and Mr 1 , and reflected lights of the detecting light “T” and the distance measuring light “M” on the projection end face are Tr 2  and Mr 2 , respectively. Further, although not shown, in the narrow-angle image  73  when the angular difference “θ”=0° (in case of  FIG. 9B ), the projection end face reflected images Mr 2  and Tr 2  are not shown in the narrow-angle image  73  because the projection end face reflected images Mr 2 , Tr 2  are far outside a field angle (a field of view) of the narrow-angle image  73 . 
     In  FIG. 9C , the intersection of the cross-hairs  74  is an image position of the deflection reference optical axis O on the end faces of the wavelength dispersion compensation prisms  55  and  58 . Mr 1  denotes an incidence end face reflection image of the distance measuring light  37  (see  FIG. 1 ), Tr 1  denotes an incidence end face reflection image of the detecting light  47  (see  FIG. 1 ), Mr 2  denotes a projection end face reflection image of the distance measuring light  37 , and Tr 2  denotes a projection end face reflection image of the detecting light  47 . Further, since the detecting light  47  has a spread angle larger than a spread angle of the distance measuring light  37 , the end face reflection images Tr 1  and Tr 2  of the detecting light  47  are larger than the end face reflection images Mr 1  and Mr 2  of the distance measuring light  37 . 
       FIG. 9D  shows the narrow-angle image  73  in a case where the wavelength dispersion compensation prisms  55  and  58  are integrally rotated (the rotation ω) in a state where the angular difference “Θ” of the wavelength dispersion compensation prisms  55  and  58 =180° is maintained, that is, a state where both the incidence end face reflection images Mr 1 , Tr 1  and the projection end face reflection images Mr 2 , Tr 2  can be acquired within the field of view of the narrow-angle image  73 . It is to be noted that, in  FIG. 9D , the incidence end face reflection image Tr 1  and the projection end face reflection image Tr 2  are not shown. 
     The detection of a fluctuation in the wavelength dispersion compensation prism  55  can be acquired based on a change in the incidence end face reflection image Mr 1  in the narrow-angle image  73  when the wavelength dispersion compensation prism  55  is solely rotated. That is, the incidence end face reflection image Mr 1  draws a circular locus around the rotating shaft  52  at a predetermined position and a predetermined size in the narrow-angle image  73  in correspondence with the magnitude of a fluctuation. The arithmetic control module  16  can calculate a fluctuation of the wavelength dispersion compensation prism  55  based on the locus. It is to be noted that, since the incidence end face reflection image Tr 1  also changes similarly the incidence end face reflection image Mr 1 , the fluctuation of the wavelength dispersion compensation prism  55  can be calculated even with the use of the incidence end face reflection image Tr 1 . 
     Further, as the method to the detection of the fluctuation of the wavelength dispersion compensation prism  58 , the wavelength dispersion compensation prisms  55  and  58  are first integrally rotated in a state where the angular difference “Θ”=180° is maintained. Thereby, the arithmetic control module  16  detects the fluctuations of the incidence end face reflection images Mr 1 , Tr 1  and the fluctuations of the projection end face reflection images Mr 2 , Tr 2  at the same time. Next, the arithmetic control module  16  solely rotates the wavelength dispersion compensation prism  58 , and detects the fluctuation of the projection end face reflection image Mr 2 , Tr 2  at this time. Subsequently, by removing the fluctuations of the incidence end face reflection images Mr 1 , Tr 1  of the wavelength dispersion compensation prism  55  obtained earlier based on the detected fluctuations of the projection end face reflection images Mr 2 , Tr 2 , the arithmetic control module  16  enables calculating the fluctuation of the wavelength dispersion compensation prism  58 . It is to be noted that the incidence end face reflection images Mr 1 , Tr 1  and the projection end face reflection images Mr 2 , Tr 2  can be identified by the arithmetic control module  16  via the image processor  24  based on a beam diameter or the reflection intensity with respect to the narrow-angle image pickup element  51 . 
     In a case where the fluctuations of the wavelength dispersion compensation prisms  55  and  58  have been detected, an influence of shaft deviations of the rotating shaft  52  or an influence of face tangle errors of the wavelength dispersion compensation prisms  55  and  58  can be removed based on the detected fluctuations. Therefore, a measurement result of the surveying instrument  1  can be corrected. Further, the calculated fluctuations can be stored in the storage module  17 , and the calculated fluctuations can be applied to subsequent measurements. 
     Further, based on a detection result of the attitude detector  18 , a measurement result of the surveying instrument  1  can be converted (corrected) to three-dimensional coordinates with reference to the horizontality. 
     It is to be noted that, as to the rotation for the fluctuation detection of the incidence end face of the wavelength dispersion compensation prism  55  and the fluctuation detection of the projection end face of the wavelength dispersion compensation prism  58 , a rotation angle of the disk prism  53  can be used as a rotation angle for the incidence end face reflection, and a rotation angle of the disk prism  54  can be used as a rotation angle for the projection end face. By using these rotation angles, the arithmetic control module  16  enables easily setting the rotation with the angular difference “Θ” of the wavelength dispersion compensation prisms  55  and  58  being maintained at approximately 180°. That is, based on the rotation angles of the disk prisms  53  and  54  when the angular difference “8” is approximately 180°, by rotating one disk prism in the same direction by an amount which the other disk prism is rotated, the arithmetic control module  16  enables easily setting the rotation with the angular difference “Θ” being maintained at 180°. 
     As described above, in the first embodiment, to detect the fluctuations of the wavelength dispersion compensation prisms  55  and  58  with respect to the rotating shaft  52 , that is, a shaft deviation, a face tangle error or the like based on a manufacturing error, the narrow-angle image  73  is used. 
     Therefore, since the narrow-angle image  73  used for the sighting or the tracking is also used for detecting fluctuations of the wavelength dispersion compensation prisms  55  and  58 , a detection mechanism does not have to be additionally provided, a reduction in the number of components and a reduction in manufacturing cost can be achieved. Further, the high rigidity is not required for improving a mechanical accuracy of rotating portions, and a reduction in weight of the rotating portions can be achieved. 
     Further, fluctuations of the wavelength dispersion compensation prisms  55  and  58  are detected, since a measurement result can be corrected while removing an influence of the fluctuations based on a detection result, a measurement accuracy provided by the surveying instrument  1  can be improved. 
     Next, by referring to  FIG. 10A  to  FIG. 10C , a description will be given on a second embodiment of the present invention. It is to be noted that, in  FIG. 10A  to  FIG. 10C , the same components as shown in  FIG. 9A  to  FIG. 9D  are referred by the same symbols, and a description thereof will be omitted. 
     In the first embodiment, the distance measuring light  37  and the detecting light  47  enter the incidence end face portion of the wavelength dispersion compensation prism  55 , which constitutes the optical axis deflector  26 , coaxially with the deflection reference optical axis “O”, and the light receiving optical axis  35  is also coaxial with the deflection reference optical axis “O” (see  FIG. 1  and  FIG. 2 ). In this case, the object reflection image reflected on the object, the incidence end face reflection images Mr 1 , Tr 1  of the wavelength dispersion compensation prism  55 , and the projection end face reflection images Mr 2 , Tr 2  of the wavelength dispersion compensation prism  58  overlap, respectively, and each images are shown in the narrow-angle image  73 . For this reason, in a case where the object is located at a distance, the receiving intensities of the reflected distance measuring light  38  (see  FIG. 1 ) and the reflected detecting light decrease, and the object reflection image is buried in the projection end face reflection image Mr 2 , Tr 2  and the incidence end face reflection image Mr 1 , Tr 1 , and the object reflection image may not be detected. 
     In the second embodiment, the distance measuring light  37  and the detecting light  47  are caused to enter the wavelength dispersion compensation prism  55  with a slight tilt (for instance, approximately Ks/2 with respect to a later-described detectable range Ks) with respect to the deflection reference optical axis “O” on the incidence end face portion of the wavelength dispersion compensation prism  55 . Further, the light receiving optical axis  35  is likewise tilted with respect to the deflection reference optical axis “O” in correspondence with the distance measuring light  37  and the detecting light  47 . 
       FIG. 10A  to  FIG. 10C  show a relationship between the end face reflection and the narrow-angle image  73  when the distance measuring light  37  and the detecting light  47  are caused to enter at a tilt with respect to the incidence end face of the wavelength dispersion compensation prism  55  in a state where an angular difference “Θ” of the wavelength dispersion compensation prisms  55  and  58  have become 180° (a magnification: 1).  FIG. 10A  shows reflected lights r 1 , r 2  of the incidence end face and the projection end face with respect to the distance measuring light  37  and the detecting light  47 .  FIG. 10B  shows the narrow-angle image  73  (a background image is omitted) at this time. It is to be noted that, in  FIG. 10B , an intersection of cross-hairs  74  is the deflection reference optical axis “O” on the end faces of the wavelength dispersion compensation prisms  55  and  58 . 
     Further, in  FIG. 10B , “K” denotes a reflection image of an object (an object reflection image), and “Ks” denotes a range (a field angle) of the object reflection image “K” which can be detected (tracked) by the detecting light  47 . It is to be noted that a size of the detectable range (the field angle) “Ks” is substantially equal to a size of an end face reflection image Tr 1  (or Tr 2 ) of the detecting light  47 . 
     Further,  FIG. 10C  shows a state where the end face reflection images Mr 1 , Mr 2  of the distance measuring light  37  rotate around the rotating shaft  52  in the narrow-angle image  73 . It is to be noted that the end face reflection images Tr 1 , Tr 2  of the detecting light  47  likewise rotate around the rotating shaft  52 , but the end face reflection images Tr 1 , Tr 2  are not shown in  FIG. 10C . 
     When the distance measuring light  37  and the detecting light  47  are caused to enter with respect to the incidence end face of the wavelength dispersion compensation prism  55  at a tilt, a misalignment occurs between a light receiving position of the object reflection image “K” and light receiving positions of the incident end face reflection images Mr 1 , Tr 1  and the projection end face reflection images Mr 2 , Tr 2  on the narrow-angle image pickup element  51  (see  FIG. 1 ) in correspondence with a distance to the object. Therefore, the object reflection image “K” can be separated from the incidence/projection end face reflection images Mr 1 , Tr 1 , Mr 2 , Tr 2 , and the object reflection image “K” can be easily detected. 
     It is to be noted that, since a method for calculating fluctuations of the incidence end face reflection images Mr 1 , Tr 1  with respect to the rotating shaft  52  and fluctuations of the projection end face reflection images Mr 2 , Tr 2  with respect to the rotating shaft  52  is the same as a method of the first embodiment, a description thereof is omitted. 
     In the second embodiment, since the distance measuring light  37  and the detecting light  47  are caused to enter the wavelength dispersion compensation prism  55  at a slight tilt with respect to the rotating shaft  52 , a position of the object reflection image “K” can be made different from positions of the incidence/projection end face reflection images Mr 1 , Tr 1 , Mr 2 , Tr 2  in the narrow-angle image  73 . 
     Therefore, even if a position of the measurement is far from the object and the intensity of a reflected light is small, since each end face reflection image does not overlap the object reflection image “K”, the object reflection image “K” can be clearly detected. 
     It is to be noted that, in the second embodiment, both the distance measuring light  37  and the detecting light  47  are caused to enter the wavelength dispersion compensation prism  55  at a slight tilt with respect to the rotating shaft  52 . On the other hand, any one of the distance measuring light  37  and the detecting light  47  may be caused to enter the wavelength dispersion compensation prism  55  at a slight tilt with respect to the rotating shaft  52 .