Laser telemeter

A laser telemeter having separate transmitting and receiving optical systems, and at least monocular target observation, in which a telescope optical system (5, 6) which is inserted before the transmitting optical system (2) and reduces the divergence of the transmitted beam, a telescope optical system (7, 8) which is inserted before the receiving optical system (3) and has an aperture angle adapted to the divergence of the transmitted beam and a common support frame (9) for the telescope optical systems (5, 6; 7, 8) which can be coupled at the front with the housing (10) of the laser telemeter (1) are provided.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The invention relates to a laser telemeter having separate transmitting and
 receiving optical systems, and at least monocular target observation.
 2. Description of the Related Art
 The majority of the known laser telemeters are based on the following
 principle. A collimated laser beam is produced and is directed via a
 transmitting optical system at a remote target. The laser light reflected
 by the target is picked up by the receiving optical system and fed to a
 detector. The receiving optical system is usually also used for target
 observation. Such a device is disclosed, for example, in German
 Publication DE 41 35 615 A1. A binocular observation device with a laser
 telemeter is disclosed in German Publication DE 37 04 848 A1.
 Particularly in the case of small targets, it is necessary to collimate the
 laser beam well. It is desirable for the distance-dependent size of the
 laser spot to be smaller than the cross-section of the target to be
 measured, in order both to achieve very high laser light intensity on the
 target and to selectively influence the transmitted beam by the target to
 be measured.
 The optical parameters of the transmitting optical system determine the
 divergence of the transmitted beam. The intensity of the laser light
 arriving at the detector and reflected by the target depends on the
 optical parameters of the receiving optical system, essentially on its
 diameter. The optical parameters of the transmitting and receiving optical
 systems therefore directly influence the maximum range of the laser
 telemeter.
 An increase in the range can be achieved either by increasing the laser
 power or by making the transmitting and receiving optical systems larger.
 The maximum laser power is limited on the one hand by regulations relating
 to safety for the eyes and moreover by the capacity of the energy source
 for operating the laser. The disadvantages of increasing the dimensions of
 the optical systems are the associated inconvenience of handling and
 greater weight.
 The technical complexities associated with a larger range have led to the
 development and optimization of specially designed laser telemeters for
 different ranges. The users of such devices must therefore decide on
 different devices depending on the measuring range required and may have
 to acquire several devices.
 The readiness of the devices for use additionally depends on the weather
 conditions, which may hinder the transmission of the optical radiation. A
 device designed for relatively long ranges may, under unfavorable
 circumstances therefore, also be used for shorter distances at which the
 device designed for these ranges has failed. However, the disadvantage is
 that only the limited field of view designed for more remote targets is
 constantly available for the target observation. In case of doubt, the
 users will nevertheless have to decide in favor of the technically more
 complex, and therefore more expensive, device.
 SUMMARY OF THE INVENTION
 It is therefore an object of the invention to provide a laser telemeter
 which permits the range to be increased in an economical manner,
 especially for small targets, without substantially impairing the
 convenience of handling and safety for the eyes.
 This object is achieved, according to the invention, by a laser telemeter
 comprising a transmitting optical system; a receiving optical system; a
 target observation system; a first telescope optical system before the
 transmitting optical system; and a second telescope optical system before
 the receiving optical system. The first telescope optical system reduces
 divergence of a transmitted beam. The second telescope optical system has
 an aperture angle adapted to divergence of said transmitted beam
 The laser telemeter according to the invention may have a numerical
 aperture of each of the first and second telescope optical systems adapted
 in each case to a respective transmitting or receiving optical system.
 The magnification of the first and second telescope optical systems may be
 the same.
 The laser telemeter may further comprise a common support frame for the
 first and second telescope optical systems coupled to the laser telemeter.
 The target observation system may be monocular or binocular.
 Each telescope optical system may further comprise either a positive lens
 on an object side and a negative lens on an image side or, alternatively,
 a positive lens on each side.

DESCRIPTIONS OF THE PREFERRED EMBODIMENTS
 The invention has also been disclosed in related German patent application
 No. 198 29 659.2, filed Jul. 2, 1998, which is hereby incorporated by
 reference.
 In the drawings, embodiments of the laser telemeter according to the
 invention are shown schematically. They are described in more detail below
 with reference to the Figures.
 The invention starts from a basic configuration of a laser telemeter and,
 if required, increases the range by means of a telescope optical system
 which can be inserted. Although such a telescope optical system is known
 per se from "Die Fernrohre und Entfernungsmesser" [The telescopes and
 telemeters], Dr. A. Konig, (1937), page 95, it is discussed there only
 from the point of view of a change in magnification. The positive effects
 on the intensity balance in the transmitted and received beam are not
 directly evident. However, these are of decisive importance for an
 increase in the range, in particular in the case of small targets.
 Although the change in magnification on sighting relatively remote targets
 is an advantageous secondary effect, it however appears only to affect the
 target observation with the laser telemeter.
 FIG. 1 shows the fundamental structure of a laser telemeter 1 having a
 transmitting optical system 2 and a separate receiving optical system 3,
 and monocular target observation system comprising an eyepiece 4 and
 associated optics. The receiving optical system 3 also receives light for
 target observation via the target observation system comprising the
 eyepiece 4 and associated optics. By means of suitable beam dividers which
 are not shown, it is ensured that the laser beam does not enter the
 eyepiece 4.
 The inserted telescopic system 12, comprising optical systems 5, 6, 7, 8,
 is arranged within a common support frame 9 which can be coupled with the
 housing 10 of the laser telemeter 1. In the embodiments shown in FIG. 1
 and 2, the support frame 9 is pushed onto the housing 10 at overlap 11.
 Other possibilities for detachable fastening are within the capabilities
 of a person skilled in the art, such as attachment bracket 13 shown in
 FIG. 3.
 As discussed below, the image magnification of the telescope optical system
 5, 6 before the transmitting optical system 2 differs from that of the
 telescope optical systems 7, 8 before the receiving optical system 3 in
 order to achieve optimal adaptation to the optical parameters of the basic
 device. The apertures of the two optical systems 2, 3 are likewise
 tailored to one another. This leads to different geometric dimensions of
 the telescope optical systems. The calculation of the optical parameters
 is within the customary capabilities of a person skilled in the art.
 The effect of the telescope optical system 5, 6 before the transmitting
 optical system 2 is to increase the energy density at the target by the
 reduced divergence of the transmitted beam. The increase in the light
 intensity due to the telescope optical system 5, 6 is proportional to the
 square of the telescopic magnification for the same numerical aperture of
 the combined transmitting system. In practice, this means that virtually
 the same reflected light intensity will be received by the more remote
 target as by the closer target without the telescope optical system 5, 6.
 The reflected intensity decreases as the square of the distance from the
 target, and this decreasing is compensated by the effect of the telescope
 optical system 5, 6.
 The telescope optical system 7, 8 before the receiving optical system 3 has
 the same effect as an increase in the diameter of the optical elements and
 thus increases the intensity of reflected laser radiation picked up. In
 practice, this measure means an increase in the distance range by about
 the square root of the telescopic magnification for small targets and by
 about the telescopic magnification of large targets.
 If the telescopic magnification before the transmitting optical system 2
 and before the receiving optical system 3 are chosen to be of the same
 magnitude, the change in the divergence of the transmitted beam in
 conjunction with the change in the field of view of the receiving optical
 system 3 then result overall in no change relative to the
 transmitting/receiving conditions of the basic device without a telescope
 optical system. The range increase achieved according to the invention is
 equal to the product of the magnitudes of the telescopic magnification of
 the transmitting optical system 2 and receiving optical system 3.
 If the telescopic magnification in the two optical systems is chosen to be
 of the same magnitude, the mutual orientation of the optical axes of the
 basic device and of the inserted telescope optical system 5, 6, 7, 8 is
 not critical. Even small angular deviations between the optical axes do
 not influence the increase in the range.
 Instead of the Galilean type shown, with positive lenses 5, 7 on the object
 side and negative lenses 6, 8 on the image side, an image reversal system
 comprising two positive lenses may also be chosen.
 FIG. 2 shows the basic structure of a binocular system. Since the
 transmitting optical system 2 and the receiving optical system 3 of the
 basic device are identical, it is also possible to use identically
 designed telescope optical systems 7, 8.
 As already mentioned, tolerances in the alignment and in the inclination
 are permitted within narrow limits in the orientation of the optical axes
 of the telescope optical system with those of the transmitting and
 receiving optical system. The mechanical coupling of the support frame to
 the housing of the basic device therefore need not meet high requirements.
 The FIGS. 3a and 3b provides details of one specific implementation of the
 invention. The invention, of course, is not limited to the design set
 forth in FIGS. 3a and 3b. In this implementation, lens 7 (cemented
 component) has a free diameter of 60 mm, while negative lens 8 (cemented
 component) has a free diameter of 42 mm. The focal distance attachment is
 an afocal system. A 1.43.times.magnification attachment is provided. In
 this implementation, lens 3 has a free diameter of 42 mm and a focal
 distance of 172.3 mm.
 While preferred embodiments have been described herein, modifications of
 the described embodiments may become apparent to those of ordinary skill
 in the art, following the teachings of the invention, without departing
 from the spirit and scope of the invention as set forth in the appended
 claims.