JPS6146810B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microscope reflecting objective.

Conventionally known microscope reflective objectives have a sufficient working distance, and by arranging the lens system from the sample surface to the reflective objective barrel, it is possible to have the same conjugate distance as a high-magnification reflective objective lens. For example, there is a device as shown in FIG. 1 that has a low magnification and minimizes the drop in effectiveness. In order to prevent dust from entering the objective lens, such reflective objectives generally have a dust-proof glass plate as shown by the dotted line in Figure 1.
P ₁ and P ₂ are provided. It would be better to make the dust-proof glass plate _P1 placed on the object side into an almost concentric sphere with a radius of curvature of f~2f, where f is the focal length of the objective mirror, with the concave surface facing the object. This is preferable because it can serve to correct the spherical aberration that occurs. However, when such dustproof glass plates P ₁ and P ₂ are arranged,
This is undesirable as it causes flare, ghost, etc.

In other words, if the dust-proof glass P ₁ is made of concentric spherical surfaces with a radius of curvature of about f to 2f and is placed with its concave surface facing the object side, the light beam emitted from the object surface will be directed to the incident surface of the dust-proof glass P ₁ . It is reflected back to the object plane, then re-reflected by the cover glass above the specimen, returns to the reflecting objective mirror, and reaches the image plane, where it becomes flare and ghost. Also, the beam exiting the reflecting objective is usually a loosely convergent beam. Therefore, if the dustproof glass P ₂ is placed perpendicular to the optical axis, the above luminous flux will be reflected from the dustproof glass P ₂
It is reflected by the incident surface of the mirror, and is reflected by the convex surface of the convex reflecting mirror in the reflecting objective mirror, reaching the image plane, resulting in flare and ghost.

The present invention has been made in view of the above points, and the object-side surface of the dust-proof glass placed on the object side is made a gentle convex surface with respect to the object, and the dust-proof glass placed on the image side is A microscope reflecting objective is provided which is arranged at a slight inclination with respect to the optical axis.

The details of _the microscope reflecting objective mirror of the present invention will be explained below. As _shown in _FIG . They are arranged so that their optical axes coincide with each other, and the light from the object is sequentially reflected by the plane reflecting mirror M ₃ , the concave reflecting mirror M ₁ , the plane reflecting mirror M ₃ , and the convex mirror M ₂ before reaching the image point. These objective systems have basically the same construction as the conventional example shown in FIG. Further, a first dustproof glass P ₁ having a convex surface facing the object is placed on the object side of the lens system described above, coaxially with each of the concave mirror M ₁ , the convex mirror M ₂ and the flat reflecting mirror M ₃ , and this light It is equipped with a second dustproof glass P ₂ disposed at a slight inclination with respect to the axis. And furthermore,
The radius of curvature of the object side surface of the first dustproof glass _P1 is
r ₁ , the angle between the optical axis of the second dustproof glass P ₂ and the perpendicular surface is θ, and the focal length of the entire system is f, the following conditions are satisfied: It is.

(1) 4f<r ₁ (2) 5°<θ<30° Next, the reason why the two dustproof glasses P ₁ and P ₂ are shaped and arranged as described above and the meaning of each of the above conditions will be explained. In the microscope reflecting objective of the present invention, the first
The reason why the dustproof glass P ₁ has a convex surface facing the object is to guide light from the object surface reflected by this convex surface out of the field of view. In other words, by making the surface convex, the light reflected from this surface and re-reflected by the cover glass on the specimen surface will not return to the reflecting objective, and even if it does return to the reflecting objective, it will not enter the field of view. I made it.

Now, assume that this first dustproof glass is a flat plate. FIG. 6 is a diagram drawn based on the embodiment of the present invention to be shown later. As is clear from this diagram, a parallel plane plate P' ₁ (the first dustproof plate with the convex surface facing the object side) is attached to the specimen S. (placed in place of glass)
When the light reflected from the surface of the specimen returns to the specimen surface, it all hits the position S' outside the field of view. Therefore, even if the light that is re-reflected from the specimen surface enters the reflecting objective mirror, it will not reach the field of view of the imaging plane and will not cause flare or ghost.

The above will vary somewhat depending on the relationship between NA, field of view size, and working distance, but if the entrance surface of the first dustproof glass _P1 is made convex, the flare light can be directed further out of the field of view. Therefore, in the case of a normal reflective objective mirror, flare and ghost can be removed by appropriately determining the curvature of the convex surface.

In this case, the greater the curvature of the convex surface of the first dustproof glass _P1 , the greater the effect. However, in consideration of the working distance and aberrations, if the curvature of this convex surface becomes too large, the lens action of the first dustproof glass P ₁ will become strong, which is not preferable. In other words, the stronger the lens action, the smaller the working distance and the worse aberrations. This deterioration of aberrations can be said for all aberrations, but it has a particularly large effect on chromatic aberrations.

Since the reflecting objective mirror consists only of surface reflecting mirrors, it does not have any means for correcting chromatic aberration. Therefore, if a large amount of chromatic aberration occurs in the first dustproof glass _P1 , it cannot be corrected. Therefore, the curvature of this convex surface cannot be made very strong, and it is necessary to set r ₁ >4f as shown in condition (1). If this condition (1) is not satisfied, chromatic aberration in particular worsens.

For example, using quartz, which is usually considered preferable as the material of the first dustproof glass P ₁ , and setting r ₁ = 4f,
The chromatic aberration of the reflective objective mirror shown in Example 1, other numerical values of which will be shown later, is approximately 0.01 in d−c. Therefore, the image plane magnified by a 10x objective mirror is about 0.01 x 100 = 1 mm. This value is the limit of chromatic aberration. That is, if r ₁ exceeds condition (1), chromatic aberration worsens, which is not preferable.

Next, the second dustproof glass P ₂ is tilted so that the light reflected by the incident surface of the dustproof glass P ₂ and further reflected by the convex surface of the convex mirror M ₂ will be removed from the image plane. be. In this case, it is preferable that the inclination angle θ satisfies condition (2). If this angle θ is too small and exceeds the lower limit, flare occurs.
There is no effect of preventing ghosts, and if the upper limit is exceeded, the optical path length of light passing through this dustproof glass P ₂ becomes large, which is unfavorable in terms of aberration correction.

Among the light from the object, the light rays that are reflected from the incident surface of the second dustproof glass _P2 and further reflected by the convex mirror _M2 , and which are most likely to produce flare and ghost (hard to deviate from the image plane), have the largest NA. It is.

Figure 7 shows that the inclination angle θ of the second dustproof glass P ₂ is 5.
The light ray l with the maximum NA advances as shown in the figure, and its height Y on the image plane becomes Y≈−18.5 mm in the example shown later. Since the image height (half of the field of view) of the reflecting objective is 10 mm, the flare light passes through a position slightly more than 8 mm away from the field of view. However, considering the possibility of off-axis light and diffuse reflection within the reflecting objective mirror, it is necessary that the flare light deviates from the above value. Therefore, θ>5°.

For the purpose of removing flare and ghost, the angle θ
can be as large as it is. However, when aberrations are taken into consideration, it is not preferable for θ to become too large. In other words, when a thick glass plate is inserted into the optical path, spherical aberration, astigmatism, distortion, etc. occur. In order to prevent the occurrence of these aberrations, it is necessary to prevent the optical path from becoming too long. In reality, the angle is about 30°, and anything larger than this is not desirable in terms of aberrations.
Therefore, it is necessary to set an upper limit as in condition (2).

In addition to the above conditions, it is more preferable to set the thickness d ₁ of the first dustproof glass P ₁ as in the following condition (3).

(3) d ₁ <0.4f If condition 3 is not satisfied, spherical aberration will occur due to the dustproof glass P ₁ and it will be difficult to correct it using the reflecting objective mirror.

Next, each embodiment of the reflective objective mirror of the present invention described above will be shown.

Example 1 Focal length 15.367 Conjugate distance 18.925 Maximum NA 0.25 Minimum NA 0.138 Magnification 1 10x effective rate 46.8% Working distance 21.724 r ₁ = 403.62 d ₁ = 2 r ₂ = ∞ d ₂ = 12.92 r ₃ = ∞ d ₃ = - 12.58 R ₄ = 35.583 D ₄ = 12.58 R ₅ = ∞ D ₅ = -6.42 R ₆ = -18.515 D 6 = 1.4 R ₇ = 1.24 R ₈ = 1.24 R 8 = 1.24 R ₈ = 1.24 R 8 = 1.24 R ₈ = 1.24 R 8 = 0.25 Minimum NA 0.138 Magnification 10.0 Effectiveness 46.8% Working distance 22.107 r ₁ = 1280.749 d ₁ = 1.97 r ₂ = ∞ d ₂ = 13.15 r ₃ = ∞ d ₃ = −12.58 r ₄ = 34.93 d ₄ = 12.58 r ₅ = ∞ d ₅ = -6.07 r ₆ = -17.409 d ₆ = 14 r ₇ = ∞ d ₇ = 1.24 r ₈ = ∞ Example 3 Focal length 15.371 Conjugate distance 182.984 Maximum NA 0.25 Minimum NA 0.138 Magnification 10.0 Effectiveness rate 46.8% Working distance 21. 79 r ₁ = 435.148 d ₁ = 1.79 r ₂ = ∞ d ₂ = 12.99 r ₃ = ∞ d ₃ = −12.58 r ₄ = 35.472 d ₄ = 12.58 r ₅ = ∞ d ₅ = −6.34 r ₆ = −18.418 d ₆ = 14 r ₇ = ∞ d ₇ = 0.99 r ₈ = ∞ In each of the above examples, r ₁ , r ₂ ... are the curvature radii of each surface shown in the order of the light path, and d ₁ , d ₂ ... are the curvature radius of each surface in the same way. is the distance between. Therefore, plane reflector M ₃ reflects twice, which is indicated by r ₃ and r ₅ . Further, the value of d is indicated by a negative sign when the light is directed toward the object side. Furthermore, it is preferable to use quartz as the dust-proof glass plates P ₁ and P ₂ so that they can also be used for spectroscopic analysis, since they can also be used for ultraviolet light.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional reflective objective mirror, FIG. 2 is a sectional diagram of a reflective objective mirror of the present invention, FIGS. 3 to 5 are aberration curve diagrams of each embodiment of the present invention, and FIG. 6 is a sectional diagram of a conventional reflective objective mirror. 1st
Fig. 7 is a diagram showing the state of flare light when a parallel plane plate is used as the dust-proof glass for the second dust-proof glass _P2 . be.

Claims (1)

[Claims] 1. A concave mirror, a convex mirror, and a flat reflecting mirror, all of which are surface reflecting mirrors, are arranged in order from the object side with their optical axes coinciding with each other, so that light from the object is sequentially directed to the flat reflecting mirror, the concave mirror, and the flat reflecting mirror. In a reflecting objective configured to form an image after being reflected by a reflecting mirror or a convex mirror,
A first dust-proof glass having a convex surface facing the object side is disposed coaxially with each of the reflecting mirrors on the incident side, and a second dust-proof glass inclined with respect to the optical axis is disposed on the exit side. A microscope reflecting objective mirror characterized in that both dust-proof glasses are configured to satisfy the following conditions. (1) 4f< r ₁ (2) 5゜<θ< 30゜ Where, f is the focal length, r ₁ is the radius of curvature of the object side surface of the first dustproof glass, and θ is the light intensity of the second dustproof glass. It is the angle of inclination from the plane perpendicular to the axis.