Astronomical telescope

Abstract

This invention provides a dispersion-correcting lens unit and a telescope that can maintain optical performance even when using a zenith prism. [Solution] A dispersion correction lens unit 10 used in a diagonal prism unit 3 for bending the optical path of light incident from the objective lens and directing it into the eyepiece lens 4b comprises a main body 10a that is detachably attached to the housing 3a of the diagonal prism unit 3 on the incident side of the light incident from the objective lens, and a lens body 10b supported by the main body 10a and configured to reduce the amount of shift in the focal position of the light as it passes through the diagonal prism unit 3.

Description

Technical Field

[0001] The present invention relates to a dispersion correction lens unit for a zenith prism provided in a celestial telescope and a celestial telescope.

Background Art

[0002] Conventionally, in a mainly refractive celestial telescope, a zenith mirror for changing the optical path by, for example, 90 degrees so that visual observation can be performed in a comfortable posture, or a zenith prism as shown in Patent Document 1 is known. Currently, particularly in an objective lens designed mainly for photographing or a telescope with high optical performance in which aberrations (spherical aberration, chromatic aberration) are corrected to the limit, a zenith mirror that does not newly generate aberrations by being additionally provided between the eyepiece lens and the objective lens is selected.

[0003] On the other hand, there is an increasing demand to use a zenith prism rather than a zenith mirror because light loss is small due to total reflection, and maintenance can be saved because there is little occurrence of aging deterioration and dirt.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, due to its material and optical path length, the zenith prism disperses light, and particularly in the visible light region, the focal positions of lights of each wavelength are shifted from each other, generating chromatic aberration that can be recognized visually, so that color bleeding is added to the star image. Therefore, as described above, there is a problem that it is difficult to use a zenith prism as it is in a telescope with high optical performance in which aberrations are corrected in advance.

[0006] Therefore, the present invention provides a dispersion correction lens unit that can maintain optical performance even when a zenith prism is used. Equipped with We provide astronomical telescopes. [Means for solving the problem]

[0011] An astronomical telescope according to one aspect of the present invention comprises an objective lens, a telescope tube supporting the objective lens, a diagonal prism unit provided in the telescope tube downstream of the optical path of light incident on the objective lens to bend the optical path, an eyepiece provided downstream of the diagonal prism unit, and a detachable attachment to the diagonal prism unit. The device comprises a dispersion correction lens unit, the dispersion correction lens unit comprising a main body detachably attached to the housing of the diagonal prism unit on the incident side of the light incident from the objective lens, and a lens body supported by the main body and configured to reduce the amount of shift in the focal position of the light due to the light passing through the diagonal prism unit, wherein the focal length of the objective lens is 1000 mm or less.

[0012] A telescope according to another aspect of the present invention includes an objective lens, a telescope tube supporting the objective lens, and a connection to the objective lens, downstream of the optical path of light incident on the objective lens, in the telescope tube. A zenith prism is provided to bend the optical path. unit And the aforementioned zenith prism unit The eyepiece provided on the downstream side and the zenith prism The unit comprises a dispersion correction lens unit detachably attached to the unit, the dispersion correction lens unit comprising a main body detachably attached to the housing of the diagonal prism unit on the incident side of the light incident from the objective lens, and a lens body supported by the main body and configured to reduce the amount of shift in the focal position of the light due to the light passing through the diagonal prism unit, wherein the ratio of the air equivalent length on the optical axis of the prism in the diagonal prism unit to the focal length of the objective lens is 0.02 or more. [Effects of the Invention]

[0015] The above astronomical telescope According to this, it is possible to maintain optical performance even when using a zenith prism. [Brief explanation of the drawing]

[0016] [Figure 1] This is an overall perspective view of an astronomical telescope according to an embodiment of the present invention. [Figure 2] The above images show side views of the zenith prism unit and dispersion correction lens unit of the astronomical telescope, with (a) showing the zenith prism unit before the dispersion correction lens unit is attached, and (b) showing the zenith prism unit after the dispersion correction lens unit is attached. [Figure 3]This is a spherical aberration diagram when a dispersion correction lens unit is used in the above-mentioned astronomical telescope. [Figure 4] This is another example of a spherical aberration diagram when a dispersion correction lens unit is used in the above-mentioned astronomical telescope. [Figure 5] This figure illustrates the simulation conditions used when simulating the effect of using the above-mentioned dispersion correction lens unit, where (a) shows the setting conditions for the optical path of light passing through the zenith prism, (b) shows the optical path using the dispersion correction lens of Example 1, (c) shows the optical path using the dispersion correction lens of Example 2, and (d) shows the optical path using the dispersion correction lens of Example 3. [Figure 6] The figure shows the results of an experiment simulating the effect of using the above-mentioned dispersion correction lens, where (a) shows the spherical aberration diagram when using the first example objective lens, and (b) shows the spherical aberration diagram when using the second example objective lens, assuming that neither the dispersion correction lens nor the diagonal prism is provided. [Figure 7] The figure shows the results of an experiment simulating the effect of using the above-mentioned dispersion correction lens, where (a) shows the spherical aberration diagram when using the first example objective lens, and (b) shows the spherical aberration diagram when using the second example objective lens, assuming that a diagonal prism is provided without a dispersion correction lens. [Figure 8] The figure shows the results of an experiment simulating the effect of using the above-mentioned dispersion correction lens, where (a) shows the spherical aberration diagram when the objective lens of the first example is used, and (b) shows the spherical aberration diagram when the dispersion correction lens and diagonal prism of Example 1 are installed when the objective lens of the second example is used. [Figure 9] The figure shows the results of an experiment simulating the effect of using the above-mentioned dispersion correction lens, where (a) shows the spherical aberration diagram when the objective lens of the first example is used, and (b) shows the spherical aberration diagram when the dispersion correction lens and diagonal prism of Example 2 are installed when the objective lens of the second example is used. [Figure 10]A diagram showing the results of an experiment simulating the effects when using the above-mentioned dispersion correction lens. (a) shows the spherical aberration diagram when using the objective lens of the first example, and (b) shows the spherical aberration diagram when using the objective lens of the second example and providing the dispersion correction lens and the zenith prism of Example 3.

Embodiment for Carrying Out the Invention

[0017] Hereinafter, the astronomical telescope 100 according to an embodiment of the present invention will be described. (Overall Configuration) As shown in FIG. 1, the astronomical telescope 100 includes an objective lens 1, a lens barrel 2 that supports the objective lens 1, a zenith prism unit 3 and an eyepiece 4 attached to the lens barrel 2, a mount 5 that supports the lens barrel 2, and support legs 6 extending from the mount 5. That is, the astronomical telescope 100 of the present embodiment is a refractive telescope of the Kepler type or the Galileo type. And the astronomical telescope 100 of the present embodiment further includes a dispersion correction lens unit 10 detachably attached to the zenith prism unit 3.

[0018] (Objective Lens) The objective lens 1 is a lens body for condensing light and forming an image. Here, the objective lens 1 is not limited to the case of being a singlet lens, and may be composed of a plurality of glasses bonded together, and may be an achromatic lens or an apochromatic lens that suppresses the occurrence of chromatic aberration and spherical aberration, and the dispersion correction lens unit 10 described later is suitable for the objective lens 1 including a structure for reducing aberration like these achromatic lenses or apochromatic lenses. Also, the focal length of the objective lens 1 of the present embodiment is 1000 [mm] or less, preferably 700 [mm] or less, and more preferably 500 [mm] or less.

[0019] (Lens Barrel) The lens barrel 2 houses the objective lens 1 inside at a position near its tip, and the light condensed by the objective lens 1 passes through.

[0020] (Zenith Prism Unit) The zenith prism unit 3 bends the optical path of the light incident from the objective lens 1. In the zenith prism unit 3, for example, the optical path is changed so that the emission direction is different from the incident direction of the light by 90 degrees (it may be 45 degrees). As shown in FIGS. 2(a) and 2(b), the zenith prism unit 3 includes a housing 3a detachably attached to the rear end of the lens barrel 2, that is, the downstream end of the optical path of the light incident from the objective lens 1, and a prism (zenith prism) 3b housed in the housing 3a. For convenience of explanation, in FIG. 2, a part of the housing 3a is shown in a cross-sectional view.

[0021] The housing 3a is formed with an upstream cylindrical portion 31 extending from the prism 3b to the upstream side of the optical path and a downstream cylindrical portion 32 extending from the prism 3b to the downstream side. The extending direction of the upstream cylindrical portion 31 and the extending direction of the downstream cylindrical portion 32 are perpendicular to each other. The prism 3b is a right-angle prism in this embodiment, and the glass type of the prism 3b is, for example, BK7 (borosilicate crown glass).

[0022] In the prism 3b, the optical path of the light on the optical axis incident from the objective lens 1 is bent by 90 degrees. On the optical axis, when the air equivalent length of the light before being bent by the prism 3b is L1 and the air equivalent length of the light after being bent is L2, the total air equivalent length on the optical axis in the prism 3b is L1 + L2. The "air equivalent length" is the physical thickness (distance) of the prism 3b divided by the refractive index. In this embodiment, this total air equivalent length is 20 [mm] or more and 30 [mm] or less. Therefore, when the focal length of the objective lens 1 is 1000 [mm], the ratio of the total air equivalent length in the prism 3b to the focal length of the objective lens 1 is about 0.020 or more and 0.030 or less. When the focal length of the objective lens 1 is 700 [mm], it is about 0.025 or more and 0.050 or less, and when the focal length of the objective lens 1 is 500 [mm], it is about 0.040 or more and 0.060 or less.

[0023] (Eyepiece) The eyepiece 4 has a housing 4a and an eyepiece lens 4b housed inside the housing 4a. The housing 4a is cylindrical and is inserted into and fixed to the downstream cylindrical portion 32 of the diagonal prism unit 3. The eyepiece 4 is detachably fixed to the downstream cylindrical portion 32 of the diagonal prism unit 3 by a fixing structure (not shown) using screws or the like.

[0024] (Stand) Returning to Figure 1, the mount 5 is an altazimuth mount or equatorial mount that supports the telescope tube 2 from below, and its structure is not particularly limited. Furthermore, the support legs 6 are tripods or the like that support the frame 5, but their structure is not particularly limited.

[0025] (Dispersion correction lens unit) Next, the dispersion correction lens unit 10 will be explained in detail. Returning to Figures 2(a) and 2(b), the dispersion correction lens unit 10 comprises a main body 10a which serves as a housing, and a lens body 10b which is housed and supported within the main body 10a.

[0026] The main body 10a is attached to the upstream cylindrical portion 31 on the incident side of the light entering from the objective lens 1 in the zenith prism unit 3. More specifically, it is attached to the upstream cylindrical portion 31 of the zenith prism unit 3 via a fixing mechanism M. The fixing mechanism M is a screw mechanism consisting of a female screw 31x provided on the inner surface of the upstream cylindrical portion 31 and a male screw 10x provided on the outer surface of the main body 10a.

[0027] A portion of the main body 10a is inserted into the inside of the upstream cylindrical part 31, and the male screw 10x is screwed into the female screw 31x, so that the dispersion correction lens unit 10 can be detachably attached to the diagonal prism unit 3. The fixing mechanism M is not particularly limited to a screw mechanism. The female screw 31x of the diagonal prism unit can be screwed with, for example, a bandpass filter or a neutral density filter instead of the dispersion correction lens unit 10. In other words, the dispersion correction lens unit 10 can be attached to the diagonal prism unit 3 using the female screw 31x for attaching and detaching accessories such as a bandpass filter or a neutral density filter. When the diagonal prism unit 3 is attached to the diagonal prism unit 3 and the diagonal prism unit 3 is attached to the telescope tube 2, the dispersion correction lens unit 10 is positioned between the diagonal prism unit 3 and the objective lens 1.

[0028] The lens body 10b reduces the amount of shift in the focal position of light caused by light passing through the zenith prism unit 3. That is, when the direction in which the focal position moves along the optical path as visible light passes through the zenith prism unit 3 is considered the forward movement direction, the lens body 10b is a dispersion correction lens that moves the focal position of at least one wavelength of light in the visible light region in the reverse movement direction, which is opposite to the forward movement direction. The glass type of the lens body 10b is, for example, S-TIH53 (manufactured by Ohara Corporation). The lens body 10b is designed to return the focal position in the reverse movement direction by an amount less than the amount (distance) by which the focal position moves in the forward movement direction as light passes through the zenith prism unit 3, thereby reducing the amount of shift in the focal position of light caused by light passing through the zenith prism unit 3.

[0029] In this embodiment, the lens body 10b shifts the focal positions of the first wavelength of light and the second wavelength of light, which has a shorter wavelength than the first wavelength, in the reverse direction D2. In this embodiment, the first wavelength of light is the Fraunhofer C line (wavelength: 656.3 [nm] red light), and the second wavelength of light is the F line (wavelength: 486.1 [nm] blue light). The achromatic lens is formed of a material (type of glass) and shape that shifts the focal positions of the C line and F line in the reverse direction. In this embodiment, the lens body 10b has one meniscus lens in one group, but the lens configuration can be appropriately selected, for example, one group with two elements, two groups with two elements, etc.

[0030] Here, Figures 3 and 4 show spherical aberration diagrams for telescope 100, illustrating the spherical aberration curves for line C (dashed line in Figure 3) and line F. The horizontal axis of these spherical aberration diagrams represents the ideal image plane as "0", with negative values ​​[mm] for upstream of the optical path and positive values ​​[mm] for downstream of the optical path. The vertical axis represents the pupil diameter of objective lens 1, with the center of objective lens 1 as 0 and the outermost edge of objective lens 1 as 1.

[0031] In this embodiment, as shown in Figure 3, the material and shape of the lens body 10b are selected so that the spherical aberration curve of line C and the spherical aberration curve of line F intersect in the region of 0.7 times or more the pupil diameter of the objective lens 1, which is the vertical axis of the spherical aberration diagram. Alternatively, as shown in Figure 4, the material and shape of the lens body 10b are selected so that the C line and the F line are close together in the horizontal axis direction within a range of 0.08 mm or less in the region of 0.7 times or more the pupil diameter of the objective lens 1. In other words, the lens body 10b is configured such that the focal position of line C and the focal position of line F coincide, or the distance between them is 0.08 mm or less, in the region of 0.7 times or more the pupil diameter of the objective lens 1.

[0032] (Effects and Benefits) As described above, in the astronomical telescope 100 of this embodiment, a dispersion correction lens unit 10 is detachably provided on the incident side of the light incident from the objective lens to the diagonal prism unit 3, thereby reducing the amount of shift in the focal position of the light due to the light passing through the diagonal prism unit 3. As a result, the occurrence of chromatic aberration caused by the change in refractive index of light of each wavelength due to the placement of the diagonal prism unit 3 between the objective lens 1 and the eyepiece 4 can be suppressed, and the addition of color fringing to the star image can be avoided. As a result, it is possible to maintain optical performance even when using the diagonal prism unit 3.

[0033] In particular, if the astronomical telescope 100 is a high-performance telescope designed for visual observation with pre-corrected aberrations, it can suppress chromatic aberration that is noticeable to the naked eye, making it easier to satisfy users with professional-level skills and knowledge, often referred to as "high-amateurs."

[0034] In this embodiment, the lens body 10b of the dispersion correction lens unit 10 moves the focal position for the C-line and F-line in the opposite direction as described above. The wavelengths of the C-line (long-wavelength light) and the F-line (short-wavelength light), which have wavelengths at both ends of the visible light region, are sufficiently far apart, resulting in a large difference in dispersion and clearly exhibiting chromatic aberration. Therefore, by reducing the positional shift of the focal positions of the C-line and F-line caused by adding the zenith prism unit 3 using the dispersion correction lens unit 10, the color fringing perceived during visual observation can be effectively reduced.

[0035] Furthermore, the lens body 10b of the dispersion correction lens unit 10 is configured such that the distance between the focal position of the C line and the focal position of the F line is 0.08 mm or less in the region of 0.7 times or more the pupil diameter of the objective lens 1.

[0036] In this way, in the region where more light rays pass through objective lens 1, which is 0.7 times or more the pupil diameter, the focal positions of the C-line and F-line coincide or are close together, and the back focus of the C-line and F-line coincides or is close together, allowing for the visual observation of clear star images.

[0037] Furthermore, the focal length of the objective lens 1 in this embodiment is 1000 mm or less, preferably 700 mm or less, and more preferably 500 mm or less. That is, the focal length is relatively short, the ratio of the optical path length of the prism 3b to the focal length is large, and the effect of the refractive index change due to light passing through the prism 3b becomes large. Therefore, when attaching the diagonal prism unit 3 to an astronomical telescope 100 having an objective lens 1 with such a focal length, chromatic aberration may occur in large quantities, making the use of the dispersion correction lens unit 10 in this embodiment extremely advantageous.

[0038] The present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention. For example, the lens body 10b of the dispersion correction lens unit 10 is not limited to the case where the focal positions of the C-line and F-line are shifted in the opposite direction D2, as described above, but may also be configured to shift the focal positions of three or more lights with different wavelengths, such as the e-line (green light with a wavelength of 546.1 nm), in addition to the C-line and F-line, i.e., an apochromatic lens. [Examples]

[0040] Next, referring to Figures 5 to 10, we will explain the results of an experiment in which a dispersion correction lens 210 (corresponding to lens body 10b above) was placed between the objective lens 201 (corresponding to objective lens 1 above) and the diagonal prism 203 (corresponding to prism 3b above) in an astronomical telescope, and its effect was simulated. As shown in Figure 5(a), the equivalent length of light in air before it is bent within the zenith prism 203 is denoted as L11, and the equivalent length of light in air after it is bent is denoted as L12. In this experiment, as shown in Figures 5(b) to 5(d), the simulation was performed assuming that a region of L11 + L12 exists linearly in the optical path of the light extending from the objective lens 201, passing through the zenith prism 203.

[0041] Figure 5(b) shows the optical path when the dispersion correction lens 210A is a single element in one group (Example 1), Figure 5(c) shows the optical path when the dispersion correction lens 210B is a double element in one group (Example 2), and Figure 5(d) shows the optical path when the dispersion correction lens 210C is a double element in two groups (Example 3). The specifications of these dispersion correction lenses 210 used in the simulation are as follows. · Glass type: S-TIH53 • Refractive index: 1.84666 • Lens size (diameter x center thickness): 26mm x 3mm • Compatible wavelengths: 5 wavelengths (F-line, C-line, g-line (435.8 nm), e-line (546.1 nm), d-line (587.6 nm)).

[0042] Furthermore, the first example objective lens 201A, whose characteristics are shown in the spherical aberration diagram in Figure 6(a), is assumed to be composed of 3 to 7 lenses. Note that the detailed configuration of objective lens 201A is omitted from the illustration in Figure 6(a). On the other hand, the second example objective lens 201B, whose characteristics are shown in the spherical aberration diagram in Figure 6(b), is composed of 3 lenses and is mainly intended for visual observation. In the spherical aberration diagram, the vertical axis shows the pupil diameter of objective lenses 201A and 201B, dimensionless, ranging from 0 to 1. The horizontal axis has the position of the ideal image plane as "0", with the upstream side of the optical path being negative [mm] and the downstream side of the optical path being positive [mm].

[0043] As shown in Figure 6(a), when using the objective lens 201A (3 to 7 lenses), if the dispersion correction lens 210A and diagonal prism 203 of Example 1 are not provided, the C line and F line are approximately aligned in the horizontal axis direction across the entire pupil diameter, resulting in almost no chromatic aberration. Furthermore, as shown in Figure 6(b), when using the objective lens 201B (3-lens: for visual observation), if the dispersion correction lens 210A and diagonal prism 203 of Example 1 are not provided, the C line and F line are close together in the horizontal direction across the entire pupil diameter, and intersect near 0.75 in the vertical direction, resulting in almost no chromatic aberration.

[0044] As shown in Figure 7(a), when using the objective lens 201A (3-7 lens elements), if the dispersion correction lens 210A of Example 1 is not provided and the diagonal prism 203 is provided instead, the focal position of the C line shifts to the negative side of the horizontal axis (positive movement direction D1), that is, towards the objective lens 1. Also, the focal position of the F line shifts to the positive side of the horizontal axis (positive movement direction D1), that is, away from the objective lens 1. As a result, the C line and the F line are separated in the horizontal axis direction, and chromatic aberration occurs.

[0045] Furthermore, as shown in Figure 7(b), when using the objective lens 201A (3-lens: for visual observation), if the dispersion correction lens 210A of Example 1 is not provided and the diagonal prism 203 is provided instead, the focal position of the C line shifts to the negative side in the horizontal axis direction (positive movement direction D1), that is, towards the objective lens 1. Also, the focal position of the F line shifts to the positive side in the horizontal axis direction (positive movement direction D1), that is, away from the objective lens 1. As a result, the C line and the F line intersect around 0.4 in the vertical axis direction and are significantly separated from each other in the horizontal axis direction in the region of 0.7 or higher, causing chromatic aberration.

[0046] As shown in Figure 8(a), when using the objective lens 201A (3-7 lens elements), and when the dispersion correction lens 210A and diagonal prism 203 of Example 1 are provided, the focal positions of the C and F lines shift in the reverse direction D2, which is opposite to the forward direction D1 in the horizontal axis direction, approaching the state shown in Figure 6(a). Therefore, the occurrence of chromatic aberration was suppressed compared to the case where only the diagonal prism 203 shown in Figure 7(a) is provided.

[0047] Similarly, as shown in Figure 8(b), when using the objective lens 201A (3-lens: for visual observation), and providing the dispersion correction lens 210A and diagonal prism 203 of Example 1, the focal positions of the C and F lines shifted in the horizontal axis direction in the opposite direction to the forward movement direction D1, D2, approaching the state shown in Figure 6(b). Therefore, the occurrence of chromatic aberration was suppressed compared to the case where only the diagonal prism 203 shown in Figure 7(b) was provided.

[0048] Incidentally, although Figures 6 to 8 do not show lines other than C and F, similar effects were obtained for the g line (435.8 nm), e line (546.1 nm), and d line (587.6 nm).

[0049] Similarly, when using the dispersion correction lens 210B of Example 2 (see Figure 5(c)), which has a lens configuration of 2 elements in 1 group, and the objective lens 201A (3 to 7 elements), chromatic aberration could also be reduced by the dispersion correction lens 210B (see Figure 9(a)).

[0050] Similarly, when using the dispersion correction lens 210B of Example 2 and the objective lens 201B (3-lens: for visual observation), chromatic aberration was also reduced by the dispersion correction lens 210B (see Figure 9(b)).

[0051] Furthermore, when using the dispersion correction lens 210C (see Figure 5(d)), which has a two-group, two-element lens configuration, and the objective lens 201A (3-7 lens elements), chromatic aberration could similarly be reduced by the dispersion correction lens 210C (see Figure 10(a)).

[0052] Similarly, when using the dispersion correction lens 210C from Example 3 and the objective lens 201B (3-lens system: for visual observation), chromatic aberration was reduced by the dispersion correction lens 210C (see Figure 10(b)). [Industrial applicability]

[0053] This invention astronomical telescope According to this, it is possible to maintain optical performance even when using a zenith prism. [Explanation of symbols]

[0054] 1…Objective lens 2… Telescope tube 3… Zenith Prism Unit 3a…Housing 3b... Right-angle prism (zenith prism) 4… Eyepiece 4a…Housing 4b… Eyepiece 5… Stand 6…Support leg 10…Dispersion correction lens unit 10a...Main unit 10b...Lens body (dispersion correction lens) 100…Astronomical telescope 201 (201A, 201B)... Objective lens 203... Zenith Prism 210 (210A, 210B, 210C)... Dispersion correction lens D1…Forward movement direction D2…Reverse movement direction

Claims

1. An objective lens and, The lens barrel that supports the objective lens, A diagonal prism unit is provided in the lens barrel downstream of the optical path of light incident on the objective lens, and bends the optical path. The eyepiece lens provided downstream of the zenith prism unit, A dispersion correction lens unit is detachably attached to the aforementioned zenith prism unit, Equipped with, The aforementioned dispersion correction lens unit is A main body is detachably attached to the housing of the aforementioned zenith prism unit on the side where light enters from the objective lens, A lens body supported by the main body and configured to reduce the amount of shift in the focal position of light caused by light passing through the zenith prism unit, Equipped with, An astronomical telescope in which the focal length of the objective lens is 1000 mm or less.

2. An objective lens and, The lens barrel that supports the objective lens, A diagonal prism unit is provided in the lens barrel downstream of the optical path of light incident on the objective lens, and bends the optical path. The eyepiece lens provided downstream of the zenith prism unit, A dispersion correction lens unit is detachably attached to the aforementioned zenith prism unit, Equipped with, The aforementioned dispersion correction lens unit is A main body is detachably attached to the housing of the aforementioned zenith prism unit on the side where light enters from the objective lens, A lens body supported by the main body and configured to reduce the amount of shift in the focal position of light caused by light passing through the zenith prism unit, Equipped with, A telescope in which the ratio of the equivalent length of air on the optical axis of the prism in the zenith prism unit to the focal length of the objective lens is 0.02 or greater.

3. The zenith prism unit is Housing and The prism housed in the aforementioned housing, It has, The housing forms an upstream cylindrical portion that extends upstream of the optical path from the prism, The upstream cylindrical portion is provided with a first screw thread into which a filter can be screwed. The astronomical telescope according to claim 1 or 2, wherein the main body of the dispersion correction lens unit is provided with a second screw that can be screwed into the first screw, thereby allowing the dispersion correction lens unit to be detachably attached to the diagonal prism unit.

4. When the direction in which the focal position moves along the optical path as visible light passes through the zenith prism unit is defined as the positive direction of movement, The astronomical telescope according to claim 1 or 2, wherein the lens body is configured to move the focal positions of light of a first wavelength and light of a second wavelength, which has a shorter wavelength than the first wavelength, in the visible light region in a reverse movement direction opposite to the forward movement direction.

5. The astronomical telescope according to claim 4, wherein the light of the first wavelength is the Fraunhofer C line, and the light of the second wavelength is the Fraunhofer F line.

6. The astronomical telescope according to claim 5, wherein the lens body is configured such that, in a region of 0.7 times or more the pupil diameter of the objective lens, the focal position of the C line and the focal position of the F line coincide, or the distance between the focal position of the C line and the focal position of the F line is 0.08 mm or less.

Images