Equatorial mount

Abstract: An equatorial mount comprising a pedestal 1, a polar shaft 2 rotatably supported on said pedestal 1 so as to extend toward the celestial north pole, a support barrel 3a fixed to said polar shaft so as to extend therefrom at a right angle, a second shaft 3 rotatably supported in said support barrel 3a, a second support barrel 4a fixed to one end of said second shaft 3 so as to extend therefrom at a right angle, a third shaft 4 rotatably supported in said second support barrel 4a for supporting a telescope 10, 10' on its free end, a crank 5 mounted on the other end of said second shaft 3 so as to extend sideways, and counterweights 6, 7 coupled to said crank so as to be disposed on a line extending from a line 96 connecting a steady point 3X and the center of gravity 9a of the telescope 10, 10' so as to balance with the weight of the telescope.

Description: This invention relates to an equatorial mount for supporting a binocular reflecting telescope which is a variant of a Cassegrain or Schmidt-Cassegrain reflector. As a conventional astronomical binocular, there is known a right-angle view refracting binocular. It uses a roof (Amici) prism and a parallelogrammic prism. The light beam from an objective lens is reflected by the roof (Amici) prism and guided to an eyepiece through a parallelogrammic prism. Another type of conventional binocular comprises a Cassegrain reflector. This reflecting telescope comprises a Cassegrain telescope tube housing two primary mirrors having small holes, and two secondary mirrors and Porro prisms combined with the telescope tube. The light reflected by the primary mirrors is reflected again by the secondary mirrors for condensing, passed thorough the small holes, reflected by the Porro prisms and guided to eyepieces. Such binoculars have to be supported on a rather large equatorial mount if they are large-apertured ("large" usually means more than 500 mm). An equatorial mount generally has a telescope tube rotating device mounted on one end of a declination shaft so as to be rotatable about a polar axis to rotatably support such a binocular. But, with the binoculars using a roof (Amici) prism or a Porro prism, the back focus behind the primary mirror has to be considerably long corresponding to the length of the prism light path. Thus, they tend to be long in the focal length and narrow in the visual field. Another problem is that the eyepieces are rotated as the telescope is turned. This means that when mounted on an equatorial mount, as the telescope is turned following the diurnal motion of a heavenly body, an observer is forced to incline his head and take an unnatural body position. Further, a conventional equatorial mount having a telescope tube rotating device tends to be large in size and heavy, so that it is difficult to operate, and is also expensive. An object is to provide an equatorial mount for supporting a telescope which has a greater degree of freedom of rotation than a conventional German style equatorial mount, which is sufficiently light in the total weight including the counterweights for keeping its weicht balance and thus is easy to operate and which is inexpensive. According to the invention there is provided an equatorial mount comprising a pedestal, a polar shaft rotatably supported on the pedestal so as to extend toward the celestial north pole, a support barrel fixed to the polar shaft so as to extend therefrom at a right angle, a second shaft rotatably supported in the support barrel, a second support barrel fixed to one end of the second shaft so as to extend therefrom at a right angle, a third shaft rotatably supported in the second support barrel for supporting a telescope on its free end, a crank mounted on the other end of the second shaft so as to extend sideways, and counterweights coupled to the crank so as to be disposed on a line extending from a line connecting a steady point and the center of gravity of the telescope so as to balance with the weight of the telescope. The mount according to the invention has three rotary shafts, i.e. the polar shaft, second shaft and third shaft, to rotate the binocular reflecting telescope mounted thereon. The combination of the three shafts makes it possible to observe any direction in the celestial globe. With a prefered binocular reflecting telescope light is guided out of the primary optical axis from the point between the primary mirror and the secondary mirror and the inverted image is converted into an erect real image by means of the erect real image forming means. The erect image thus obtained is viewed through the rotatable eyepiece mechanism. This makes it possible to shorten the distance from the secondary mirror to the focal point and thus to provide a wide-angled and short-focus telescope irrespective of its aperture size. Such a binocular reflecting telescope is simple in structure and inexpensive and allows an operator to observe celestial bodies without inclining his head or body. The mount according to the present invention is used to support binocular reflecting telescopes. It has three rotary shafts combined together so that the telescope mounted thereon can be turned to any direction of the celestial globe, while keeping the primary telescope tubes so that the eyepieces are kept horizontal to the observer's eyes. The mount and the prefered telescope form an observing device which is low-cost and very easy to operate. Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of an entire binocular reflecting telescope as mounted on an equatorial mount of an embodiment of the present invention; Fig. 2 is a side view of the same; Fig. 3 is a front view of the same (but the equatorial mount omitted); Fig. 4 is a sectional view taken along line IV-IV of Fig. 3; Fig. 5 is a sectional view taken along line V-V of Fig. 3; Fig. 6 is a sectional view taken along line VI-VI of Fig. 3; Fig. 7 is a sectional view taken along line VII-VII of Fig. 3; Fig. 8 is a front view of a partially modified embodiment in which long-focus eyepieces are used; Fig. 9 is a view explaining the operation; Fig. 10 is another view explaining the operation; Fig. 11 is a view explaining how astronomical observation is made. Now we will describe embodiments of the present invention with reference to the drawings. Fig. 1 is a perspective view of a binocular reflecting telescope mounted on an equatorial mount according to the present invention. The equatorial mount will be described after the description of the prefered binocular reflecting telescope. In Figs. 1 to 7 numerals 10 and 10' designate primary telescope tubes. The one on the left of Fig. 1 is designated hereinafter as a first primary telescope tube 10 and the one on the right is designated as a second primary telescope tube 10'. The first and second primary telescope tubes 10, 10' are longitudinally offset by a predetermined distance from each other and contain primary mirrors 11, 11' and secondary mirrors 12, 12'. Fixed barrels 13, 13' are mounted in the joint area between the first and second primary telescope tubes 10, 10' so as to be aligned with each other as viewed from front (Fig. 3). The lights reflected by the primary mirrors 11, 11' and the secondary mirrors 12, 12' are guided out of the main optical axis through the fixed barrels 13, 13'. Further, tumblers 14, 14' and eyepieces 15, 15' are connected. Numerals 16, 16' designate dials for fine focus adjustment. Figs. 2 and 3 are their side view and front view, respectively. Fig. 4 is a sectional view taken along line IV-IV of Fig. 3. It shows the internal structure of the binocular reflecting telescope which is associated with the first primary telescope tube 10. The following description will be made mainly for the first primary telescope tube 10. As to the second primary telescope tube 10', description will be made of only parts which are different from those of the first primary telescope tube 10. The primary mirror 11 and the secondary mirror 12 are mounted in the first primary telescope tube 10. In the Schmidt-Cassegrain type, it is necessary that the primary mirror 11 have a spherical surface, the secondary mirror 12 have a hyperboloidal surface and a correcting plate 12a be in the form of a high-order aspherical lens (shown by chain line). In the Cassegrain type, the correcting plate 12a is not used, the primary mirror 11 has a paraboloidal or ellipsoidal surface and the secondary mirror 12 has a hyperboloidal or spherical surface. The primary mirror 11 is mounted on one end of the telescope tube by means of a primary mirror cell 11a. A third mirror 17 and a fourth mirror 18, which are elliptically shaped plane mirrors, are mounted in the first primary telescope tube 10 at substantially the central part thereof and in the fixed barrel 13, respectively. In this embodiment, these two plane mirrors serve as a means for forming an erect real image. The third mirror 17 is supported on a support member 17a extending from the primary mirror cell 11a along a first optical axis (Fig. 4) while the fourth mirror 18 is supported on an oblique support plate 18a mounted in the fixed barrel 13 (Fig. 5). The third mirror 17 and the fourth mirror 18 are arranged so as to be perpendicular to each other so as to contain a line of intersection extending in the direction of vector V0 (Fig. 5). In the tumbler 14 mounted on the top end of the fixed barrel 13 are mounted a pair of parallel mirrors 19a, 19b (Fig. 4). An elliptical hole 20 is formed in the primary telescope tube 10. The tumbler 14 is mounted by means of a flanged pedestal 14a and a pin 14c having its axis aligned with a third optical axis in the filxed barrel 13 so as to be rotatable with respect to the fixed barrel 13 around the third optical axis. The flanged pedestal 14a is journaled on a ring-shaped bearing. Its opening serves as an entrance port for the light guided from the fixed barrel 13. The pin 14c is provided on a support plate 14b mounted on the fixed barrel 13. The above-described rotary support mechanism can minimize the length of the third optical axis in the fixed barrel 13. The light along the third optical axis is reflected by the parallel mirrors 19a, 19b and guided to the eyepiece 15, which has a focus adjustment mechanism comprising a dial 16 provided at its tip with a pinion 16a in engagement with a rack 15b mounted on an eyepiece barrel 15a. For focusing, the eyepiece 15 is moved up and down by turning the dial:16 manually. The parallel mirrors 19a, 19b shown in Figs. 4 and 6 may be replaced with rectangular prisms 19c, 19d shown by dotted lines. The angle  (Fig. 4) between the third optical axis of the light beam reflected by the fourth mirror 18 and the first optical axis is 60°, and the angle formed between the first axis and the line of intersection defined if the third mirror 17 and the fourth mirror are brought together imaginarily, which is /2, is 30°. The  and /2 may be 45° and 22.5°, 90° and 45° or 120° and 60°. Fig. 5 shows a sectional view taken along line V-V of Fig. 3. As will be apparent from this figure, the third mirror 17 and the fourth mirror 18 are arranged such that their normal lines are perpendicular to each other. Thus, a second optical axis along which the light reflected by the third mirror 17 passes is oblique to the fourth mirror 18 in the fixed barrel 13 mounted in the joint area between the right and left primary telescope tubes 10, 10'. Figs. 6 and 7 are sectional views of the second primary telescope tube 10' and correspond to Figs. 4 and 5. It is apparent from these figures that the fixed barrel 13' is in alignment with the fixed barrel 13 of Fig. 4 on the joint surface between the primary telescope tubes 10, 10'. Thus, as shown in Fig. 2, the lengths of the fixed barrels 13, 13' are different from each other to a degree depending on according to the angle of inclination  (the smaller the angle , the larger the difference in lengths; only if the angle  is 90°, the barrels 13, 13' have the same length). As will be apparent if one compares Figs. 5 and 7, the second optical axes in the first primary telescope tube 10 and the second primary telescope tube 10' are inclined in opposite directions toward the joint area between the primary telescope tubes 10, 10'. This arrangement is employed for the following reasons. As will be apparent from Figs. 2 and 3, the lights are guided into the eyepieces 15, 15' by reflecting them by the parallel mirrors in the tumblers 14, 14', which are rotatable about the third optical axes, so that an observer can keep the heights of his eyes always on the same level. Since the interpupillary distance of the human eyes is 62 mm on the average, even if the first and second primary telescope tubes 10 and 10' are inclined, observation is carried out by rotating the tumblers 14, 14' so that an observer can set the eyepieces 15, 15' to his eyes. The centers of rotation of the tumblers 14, 14' (which coincide with the third optical axes) may be disposed on lines perpendicular to the primary optical axes of the first and second primary telescope tubes or may be disposed near lines that extend parallel to the primary optical axes on the joint surface between the first and second primary telescope tubes. In this example, the latter arrangement is employed. This is the reason why the second optical axes are inclined with respect to the joint surface. The distance between the centers of rotation of the tumblers 14, 14' is preferably 10 to 15 cm taking into account the interpupillary distance of an average person and the size of the eyepieces. Fig. 8 shows a modified example in which long-focus eyepieces are used. The larger the eyepieces, the larger the tumblers 14, 14' have to be. Thus, in order to prevent them from interfering against each other, the tumblers 14, 14' have their central parts constricted like iron dumbells. The third axes, which are the centers of rotation of the tumblers 14, 14', are also disposed outwardly apart from each other. In this example, since the tumblers 14, 14' are large in size, long-focus, wide-angle eyepieces 15, 15' can be used. Now referring to Figs. 1 and 2, description will be made of the equatorial mount of the present invention. The equatorial mount shown comprises a pedestal 1, a polar shaft (first shaft) 2 supported obliquely by the pedestal 1, a second shaft 3 rotatably supported in a support barrel 3a coupled to the polar shaft 2, and a third shaft 4 rotatably supported in a second support barrel 4a provided at the bottom end of the support barrel 3a (see Fig. 2). Conterweights 7 are screwed onto a threaded rod 8a extending from the free end of a V-shaped crank 5 mounted on the free end of the second shaft 3 in a direction away from the steady point 3X. Another counterweight 6 is screwed onto a threaded rod 8b mounted inside of the crank 5 and extending in the same direction as the crank 5. Let us suppose here that the equatorial mount of Fig. 2 is located in lat. 30° N. (or lat. 30° S.). In the embodiment, the polar shaft 2 extends toward the celestial north pole (or south pole) and is rotatable following the diurnal rotation of the celestial body. The second shaft 3 is mounted in the support barrel 3a, which is secured to the end of the polar shaft 2 so as to be perpendicular to the polar shaft, and is rotatably supported by bearings 3b mounted on both ends of the support barrel 3a. Though not shown, the support barrel 3a has a clamp for unrotatably holding the second shaft 3 with respect to the support barrel 3a at a desired angle. The second support barrel 4a of the third shaft 4 is integral with the second shaft 3 at its bottom end. The second support barrel 4a is also provided with a clamp. The two kinds of counterweights 6, 7, which are screwed onto the threaded rods 8a, 8b, connected to the crank 5, are arranged perpendicular to each other. In the figure is shown one counterweight 6 and two counterweight 7. But the numbers of the respective counterweights should be adjusted according to the weight (size) of the binocular reflecting telescope. Also, they are moved along the threaded rods 8a, 8b to positions where they balance with the binocular reflecting telescope. The binocular reflecting telescope of the example is used for astronomic observation in the following manner. As shown in Fig. 4, the light coming into the front ends of the primary telescope tubes 10, 10' is reflected by the primary mirrors 11, 11' and the secondary mirrors 12, 12'. The image formed by the thus reflected light is inverted. But the light collected and converged by the secondary mirrors is reflected by an erect image creating means comprising the third mirror 17 disposed on the first optical axis and the fourth mirror 18 on the second optical axis. The light thus reflected produces an erect image. An erect image is created by setting the value  at 60° in the embodiment. As shown in Figs. 4 and 5, the light beam reflected by the secondary mirror 12 is propagated along the first optical axis and reflected by the third mirror 17, whose normal line is denoted Q3, the incident angle and the reflecting angle both being 69°. The light beam is then propagated along the second optical axis, passes through an elliptic hole 20 formed in the primary telescope tube 10, and impinges on the fourth mirror 18 having a normal line Q4 and supported by the support plate 18a. The light beam is reflected by the fourth mirror 18 at both the incident angle and the reflecting angle of 69° and is now propagated upwards along the third optical axis, which forms an angle of 60° with respect to the primary axis. The light converted into an erect image is reflected by the pair of parallel mirrors 19a, 19b in the tumblers 14, 14' and guided into the eyepieces 15, 15'. An observer can see the light image thus formed by turning the focusing dials 16, 16'. An observer manually controls the right and left primary telescope tubes 10, 10' and the tumblers 14, 14' so as to direct the telescope at a target object in the celestial globe. Of course, a motor may be coupled to each of the rotary shafts to control the telescope automatically, instead of manually, with a computer. In the state shown in Fig. 9, the telescope is mounted on the equatorial mount so that its primary telescope tubes 10, 10' are inclined by 30° with respect to the vertical line. In the tumblers of the telescope shown, no focusing device is mounted. Instead of providing such focusing devices in the tumblers, motors M, M' may be mounted on the secondary mirrors in the primary telescope tubes so as to adjust the focus by moving the secondary lenses back and forth in a straight line. If only the primary telescope tubes 10, 10' are inclined following the movement of the celestial globe while not rotating the tumblers 14, 14' from the position shown in Fig. 3, the eyepieces 15, 15' will be moved to different heights from each other, so that an observer will be forced to incline his head. The telescope of the example is free of this problem because the eyepieces 15, 15' can be rotated independently of each other by the respective tumblers 14, 14'. Namely, the eyepieces 15, 15' can be moved to positions level with each other as shown in Fig. 3 by manually rotating the tumblers. Thus, an observer does not have to incline his head when making telescopic observations. Fig. 10 shows a state in which the primary telescope tubes 10, 10' are turned to their horizontal position opposite to the position shown in Fig. 9. Any more detailed description is omitted. The binocular reflecting telescope of the example is mounted on the equatorial mount shown in Figs. 1 and 2 and used for astronomic observation in the following manner. As shown in Fig. 11, the polar shaft 2 of the equatorial mount shown in Fig. 2 is directed toward e.g. the celestial north pole (or south pole) to observe stars that make diurnal rotations as shown by locus A which extends along the celestial equator. The equatorial mount shown in Fig. 2 has a greater degree of freedom of rotation compared with a German-style equatorial mount, which has a right-ascention shaft and a declination shaft, because it has the third shaft 4 in addition to the above two shafts. Thus, a celestial body that passes the locus A shown in Fig. 11 can be observed simply by turning only the polar shaft 2. But a celestial body such as one that follows the locus B will not come within the range of telescope simply by turning the polar shaft 2. In order to observe a celestial body that makes a dirunal rotation passing the zenith such as locus B, the polar shaft 2 is turned by 90° in the direction of diurnal rotation (the direction of arrow E in Fig. 11), the second shaft 3 is then turned by 30° in the direction of arrow F, and finally the third shaft 4 is turned by 90° in the direction of arrow G. In this state, the primary telescope tubes 10, 10' are trained on the zenith while the eyepieces 15, 15' are kept level with each other. When an observer puts his eyes on the eyepieces 15, 15' kept level with each other, the primary telescope tubes 10, 10' will rotate together with the polar shaft 2, which is driven by a diurnal rotation tracking device, until the target object comes into view. The equatorial mount used for astronomical observation has, as shown in Fig. 2, a threaded rod 8a mounted on the free end of the V-shaped crank 5 and extending along an extension line aligned with the line connecting the center of gravity 9a of the telescope and the steady point 3X. Counterweights 7 are screwed onto the threaded rod 8a. Another threaded rod 8b is mounted inside the crank 5 so as to extend parallel thereto. Another counterweight 6 is screwed on the rod 8b. In order to keep the counterweights 6 and 7 in a balanced state about the steady point 3X, the center of gravity of the combined mass of counterweights 6 and 7 has to be disposed on an equilibrium straight line 9b passing the steady point 3X and the center of gravity of 9a of the telescope. By adding counterweights 6 and 7 only to the crank 5, the total weight of counterweights used can be reduced by about half compared with the case where weights are attached to the bottom end of the third shaft (K in Fig. 2).

Claims: An equatorial mount comprising a pedestal (1), a polar shaft (2) rotatably supported on said pedestal (1) so as to extend toward the celestial north pole, a support barrel (3a) fixed to said polar shaft so as to extend therefrom at a right angle, a second shaft (3) rotatably supported in said support barrel (3a), characterised by a second support barrel (4a) fixed to one end of said second shaft (3) so as to extend therefrom at a right angle, a third shaft (4) rotatably supported in said second support barrel (4a) for supporting a telescope (10, 10') on its free end, a crank (5) mounted on the other end of said second shaft (3) so as to extend sideways, and counterweights (6, 7) coupled to said crank so as to be disposed on a line extending from a line (96) connecting a steady point (3X) and the center of gravity (9a) of the telescope (10, 10') so as to balance with the weight of the telescope.

Inventors: MASUNAGA SHUICHI, MASUNAGA SUMIE, MASUNAGA, SHUICHI, MASUNAGA, SUMIE
Applicants: MASUNAGA SHUICHI, MASUNAGA SUMIE, MASUNAGA, SHUICHI, MASUNAGA, SUMIE
Application year: 1993
Main classification: G02B23
IPC codes: G02B17, G02B23