Optics: measuring and testing – Range or remote distance finding – With photodetection
Reexamination Certificate
2002-10-29
2004-06-08
Tarcza, Thomas H. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
With photodetection
C356S004010, C356S005010
Reexamination Certificate
active
06747733
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic distance meter having a sighting telescope.
2. Description of the Related Art
When a surveyor measures the distance between two points, an electronic distance meter (EDM) is generally used. An electronic distance meter calculates the distance via the phase difference between a projecting light and a reflected light and via the initial phase of an internal reference light, or via the time difference between the projecting light and the reflected light.
A typical electronic distance meter is provided, behind the objective lens of a sighting telescope thereof, with a light transmitting/receiving mirror positioned on the optical axis of the sighting telescope, a light emitting element which emits a measuring light to transmit the same toward a target via the light transmitting/receiving mirror, and a light receiving element which receives the light that is reflected by the target and not interrupted by the light transmitting/receiving mirror.
In such an electronic distance meter, the light which is reflected by the target and passed through the objective lens of the sighting telescope is interrupted by the light transmitting/receiving mirror. Various proposals to prevent this problem from occurring have been known in the art. For instance, the following first and second proposals are known in the art. The first proposal is to make the measuring light have an asymmetrical beam profile with respect to a point, while the second proposal is to transmit the measuring light toward a target along an optical path which is displaced slightly from the optical axis of the sighting telescope.
However, according to the first proposal, if the measuring light has an asymmetrical beam profile with respect to a point by a light-shield mask disposed in an optical path between the light emitting element and the light transmitting/receiving mirror, light rays of the measuring light which are passed through the light-shield mask interfere with each other to produce diffraction fringes at a measuring point. At this time, reflections of the produced diffraction fringes become noise depending on the distance to the point of measurement or terms and conditions of the measuring point, deteriorating the accuracy of distance-measurement. On the other hand, in an electronic distance meter using the measuring light as a pointer for collimation, due to the measuring light having an asymmetrical beam profile with respect to a point, it is difficult to visually perceive the center of the measuring light spot on the target.
According to the second proposal, it is difficult to use the measuring light toward the target as a pointer for collimation since a central ray of the measuring light is displaced from the optical axis of the sighting telescope.
SUMMARY OF THE INVENTION
The present invention has been devised in view of the problems noted above, and accordingly, the present invention provides an electronic distance meter which makes it possible to measure distances with a high degree of precision without being influenced by terms and conditions of the measuring point. The present invention also provides an electronic distance meter in which it is easy to visually perceive the center of the measuring light spot on the target when the measuring light is used as a pointer for collimation.
For example, an electronic distance meter is provided, including a sighting telescope optical system having an objective lens for sighting an object, and an optical distance meter which includes a light-transmitting optical system for transmitting a measuring light toward the object via the objective lens, and a light-receiving optical system for receiving a portion of the measuring light which is reflected by the object. The light-transmitting optical system includes a light-shield mask having a translucent portion to define a beam profile of the measuring light. The translucent portion includes a filter having an uneven density, light transmittance of a central portion of the filter being greater than light transmittance of a peripheral portion of the filter.
It is desirable for the filter to be a neutral density filter.
It is also desirable for the light transmittance of the filter to have a Gaussian distribution.
The translucent portion can be in the shape of a rectangle, a triangle, a circle or an ellipse.
The electronic distance meter can further include a diffraction mask having at least one diffraction aperture which causes diffraction fringes on the measuring light passed therethrough, and a mode selecting device for switching between a pointer mode in which the diffraction mask is inserted into a distance-measuring optical path and a distance measuring mode in which the diffraction mask is retracted from the distance-measuring optical path.
The diffraction aperture can be in the shape of a rectangle, a triangle, a circle or an ellipse.
The light-transmitting optical system can include a second neutral density filter for adjusting the amount of the measuring light which is transmitted toward the object.
The second neutral density filter can include a rotary disk having a rotational axis extending parallel to said distance-measuring optical path, wherein the rotary disk is provided with the diffraction aperture and an arc-shaped ND filter portion. Both of the diffraction aperture and the arc-shaped ND filter portion are positioned on and along a circle having a predetermined radius about the rotational axis. The light transmittance of the arc-shaped ND filter portion continuously varies in a circumferential direction thereof. A central ray of the measuring light intersects the circle and incidents upon the center of the diffraction aperture or the centerline of the arc-shaped ND filter portion in accordance with rotational position of the rotary disk.
It is desirable for the electronic distance meter to include a mask driver which rotates the rotary disk to insert the arc-shaped ND filter portion into the distance-measuring optical path when in the distance measuring mode, and to inserts the diffraction aperture into the distance-measuring optical path when in the pointer mode.
The diffraction aperture can include a plurality of diffraction apertures having different shapes, and wherein the mask driver selects a diffraction aperture from among the plurality of diffraction apertures and inserts the selected diffraction aperture into the distance-measuring optical path in the pointer mode.
It is desirable for the electronic distance meter to include a controller which actuates the mask driver in accordance with an object distance.
It is desirable for the electronic distance meter to include a focus detecting device for detecting a focus state of the sighting telescope optical system, wherein the controller actuates the mask driver in accordance with the focus state detected by the focus detecting device.
The translucent portion can be in the shape of a cross or a star.
It is desirable for the light transmittance of the filter to decrease in radial directions from an approximate center of the translucent portion toward an edge thereof.
It is desirable for the optical distance meter to include a light source which emits the measuring light to travel in a distance-measuring optical path therealong.
The rotary disk can include a plurality of slits at equi-angular intervals about the rotational axis, the plurality of slits being used to sense a rotational position of the rotary disk.
According to another embodiment, an electronic distance meter is provided, including a sighting telescope optical system having an objective lens for sighting an object, an optical distance meter including a light-transmitting optical system for transmitting a measuring light toward the object on an optical axis of the objective lens there along, and a diffraction mask having at least one diffraction aperture which causes the measuring light to produce diffraction fringes.
The diffraction aperture can be in the shape of a rectangle, a triangle, a cir
Shirai Masami
Suzuki Shin'ichi
Takayama Homu
Ueno Masayuki
Andrea Brian
Greenblum & Bernstein P.L.C.
PENTAX Corporation
Tarcza Thomas H.
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