JPH0411848B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a microscope objective lens with a magnification of 100 times and an NA of 0.95. As a conventional microscope objective lens having the same lens type as the lens system of the present invention, there is a lens system described in JP-A-51-135545. However, since this conventional example has a magnification of 40 times and the lens configuration is different, it is impossible to use it at a magnification of 100 times.
Also, the ratio of working distance to focal length is small. Another conventional example is an objective lens described in Japanese Patent Application Laid-Open No. 56-75614, and this conventional example has an objective lens with a magnification of 100 times and a lens configuration that is relatively similar to that of the present invention. There are things that exist. However, the Petzval sum is positive and the image plane flatness is not good. The present invention has a high magnification of 100 times, is extremely large for a drying system with a numerical aperture of NA 0.9 or more, and has a long working distance. Moreover, the present invention provides a microscope objective lens in which various aberrations are well corrected even in the periphery of the field of view. The objective lens of the present invention comprises a first group lens which is a positive single lens with a concave surface facing the object side, a second group lens which is a cemented lens of a positive lens and a negative lens, a third group lens which is a cemented lens, and a cemented lens. This is a lens system composed of a fourth group of lenses, a fifth group of positive single lenses, and a sixth group of cemented negative lenses. At least one of the third group lens and the fourth group lens is a triple cemented lens, and both the third group lens and the fourth group lens include a positive lens. Furthermore, the lens system of the present invention satisfies the following conditions (1)
Conditions (4) to (4) are satisfied. (1) 0.5＜｜r ₁ /(n ₁ −1)f｜＜2.5 (2) ν _2p , ν _3p , ν _4p ≧8.0 (3) 1＜−f ₆ /f＜3.5 (4) ν _6p − ν _6o <0 where r ₁ is the radius of curvature of the object side surface of the first group lens, n ₁ is the refractive index of the first group lens, ν _2p , ν _3p , ν _4p ,
ν _6p is the Atbe number of the positive lens in the second group lens, third group lens, fourth group lens, and sixth group lens, ν _6o is the Atbe number of the negative lens in the sixth group lens,
f is the focal length of the entire system, and f ₆ is the focal length of the sixth group lens. Each of the above conditions will be explained in detail below. Condition (1) is provided to correct spherical aberration, coma aberration, and field curvature, and if the upper limit of this condition is exceeded, the Petzval sum of the entire system becomes positively large, making it impossible to obtain a flat image surface. On the other hand, if the lower limit is exceeded, the spherical aberration and comatic aberration generated in the first lens group worsen, and cannot be corrected even in the rear lens group. Condition (2) is such that chromatic aberration is removed by using a low-dispersion material for the positive lenses of the second, third, and fourth group lenses.
In addition, in the lens system of the present invention, one of the second group lens and the third group lens among these lens groups is made into a triple cemented lens, thereby making it effective for correction of the secondary spectrum. be. If the lower limit of condition (2) is exceeded, in order to correct longitudinal chromatic aberration, the curvature of the cemented surface of each of the above groups will have to be strengthened, and other aberrations will occur, making it impossible to correct them. The next spectrum becomes larger. In the objective lens of the present invention, the power of the lens group disposed closest to the image side is made stronger than that of a normal objective lens. This lens group closest to the image side has two roles: to improve the flatness of the image and to increase the working distance. In terms of image flatness and long working distance, it is better to have a strong power in this group, but if it is too strong, aberrations will be adversely affected. Condition (3) defines the power of the sixth group lens based on the above reason, and is provided to ensure a long working distance with good aberration correction. If the upper limit of this condition is exceeded, a sufficient working distance cannot be ensured, and the field curvature in particular deteriorates, making it impossible to correct it with other groups. Conversely, if the lower limit is exceeded, spherical aberration, coma aberration, and astigmatism deteriorate. Condition (4) concerns correction of lateral chromatic aberration,
If the upper limit is exceeded, the chromatic aberration of magnification becomes so large that it cannot be corrected even if a chromatic aberration of magnification correcting eyepiece is used in combination. Furthermore, as mentioned above and as shown in condition (3), when the power of the concave lens placed closest to the image side is increased,
It is necessary to increase the power of the convex lens group placed in front of it. In the present invention, a convex lens (fifth group lens) is arranged behind the triple cemented lens,
The power of the front positive lens group is strengthened, and the light rays are smoothly bent and directed toward the concave lens (sixth group lens). In other words, this convex lens (fifth group lens) alone does not increase the overall convex power, but this lens also strengthens the overall positive power and balances the increased power of the concave lens. This is what I did. The 5th group lens is effective in this respect,
The role of this lens is also important in the objective lens of the present invention. Next, examples of the microscope objective lens of the present invention will be shown.

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[Table] However, r ₁ , r ₂ ,..., r ₁₇ is the radius of curvature of each lens surface, d ₁ , d ₂ ,..., d ₁₆ is the wall thickness and air gap of each lens, n ₁ , n ₂ ,..., n ₁₁ is the refractive index of each lens,
ν ₁ , ν ₂ , ..., ν ₁₁ are the Atsube numbers of each lens, and WD is the working distance. Among the embodiments described above, Embodiment 1 is an objective lens used in combination with other appropriate imaging lenses, and is a so-called objective lens with an infinite lens barrel length. Therefore, the aberration curve diagram of this embodiment shown in FIG. 2 shows the case where an imaging lens having the following data is added to form an image using the lens configuration shown in FIG. 4.

[Table] Furthermore, Example 2 is an objective lens with a finite lens barrel length. Therefore, the aberration curve diagram of this embodiment shown in FIG. 3 is obtained when an image is formed using only this objective lens.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the objective lens of the present invention, FIG. 2 is an aberration curve diagram of Example 1 of the present invention, FIG. 3 is an aberration curve diagram of Example 2 of the present invention, and FIG. 4 is a diagram of the aberration curve of Example 1 of the present invention.
FIG. 3 is a cross-sectional view of an example of an imaging lens used in conjunction with the imaging lens.

Claims (1)

[Claims] 1. A first group lens that is a positive single lens with a concave surface facing the object side, a second group lens that is a cemented lens of a negative lens and a positive lens, and at least one of the lenses is a triple cemented lens. a third group lens and a fourth group lens each including a positive lens; a fifth group lens consisting of a positive single lens; and a sixth group lens consisting of a negative cemented lens.
A microscope objective lens comprising a group lens and further satisfying the following conditions. (1) 0.5＜｜r ₁ /(n ₁ −1)f｜＜2.5 (2) ν _2p , ν _3p , ν _4p ≧8.0 (3) 1＜−f ₆ /f＜3.5 (4) ν _6p − ν _6o <0 where r ₁ is the radius of curvature of the object side surface of the first group lens, n ₁ is the refractive index of the first group lens, ν _2p , ν _3p ,
ν _4p and ν _6p are the Abbe numbers of the positive lenses in the second, third, fourth, and sixth group lenses, respectively; ν _6o is the Abbe number of the negative lenses in the sixth group; f is the focal length of the entire system, and f ₆ is the focal length of the sixth group lens.