JPH09197285A - Objective lens for phase difference microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To completely decrease stray light entering an image formation surface in an objective lens for a phase difference microscope having a phase plate provided with a phase film on the bonded surfaces of a pair of bonded parts whose lens surfaces coming in contact with air are plane by forming the bonded surfaces to have the radius of curvature. SOLUTION: The phase plate 1 arranged at the position of the pupil of the objective lens is constituted of a pair of bonded parts 1a and 1b, and a ring-like extinction area to lower the transmissivity of 0th order light and the phase film to modulate the phase by 90 deg. with respect to the 0th order light are formed on the bonded surfaces of the parts 1a and 1b. The outer surfaces coming in contact with the air of the parts 1a and 1b are formed as the planes and the bonded surfaces of the parts 1a and 1b are curved with the radius of curvature R. Due to the curvature of the bonded surfaces, a reflection angle obtained in the case of reflecting the 0th order light from a sample surface on the extinction area of the phase plate 1 becomes large, and the light does not enter the visual field of the image formation surface even when it is reflected by a lens group on a sample surface side again. Therefore, the lowering of contrast is restrained to the minimum.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an objective lens for a phase contrast microscope, and more particularly to a phase plate used for the objective lens.

[0002]

2. Description of the Related Art An objective lens for a phase-contrast microscope comprises an annular dimming region for reducing the transmittance of 0th-order light and a phase film for changing the phase of the 0th-order light by 90 ° at the pupil position of the objective lens. Is provided. The pupil position of the objective lens may be inside the lens or in the air, but in the latter case where the pupil position of the objective lens is in the air, the dimming region and the phase film are vapor-deposited. A phase plate in which two bonded components and a non-evaporated bonded component are bonded together is used. At that time, in the conventional phase plate, parallel-plane glass was used for both joint parts.

[0003]

Generally, a metal film is used as the annular dimming region. The light intensity of the 0th-order light that enters the objective lens from the sample is high, and the dimming region formed by the metal film has a high reflectance, so the intensity of the light reflected in the dimming region is high. Therefore, the reflected light from the dimming area is reflected on the sample surface to generate stray light, or the reflected light from the dimming area is reflected on each lens surface to generate stray light, thus lowering the contrast on the image plane. It was In order to reduce the intensity of these stray lights, the metal film in the dimming region is made a low reflection film, and the performance of the antireflection film on each lens surface is improved. However, these measures are not enough, and the contrast on the image plane cannot always be sufficiently improved. Therefore, an object of the present invention is to provide an objective lens for a phase contrast microscope in which stray light mixed in the image plane is sufficiently reduced.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, that is, the joint surfaces of a pair of joint parts whose lens surfaces in contact with air are flat are
In a phase-contrast microscope objective lens having a phase plate provided with a dimming region that reduces the transmittance of the next light and a phase film that modulates the phase by 90 ° with respect to the 0th light, the bonding surfaces of the pair of bonding components are The objective lens for a phase contrast microscope is characterized in that it is formed so as to have a radius of curvature.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows an embodiment of an objective lens for a phase contrast microscope according to the present invention, in which a phase plate 1 is arranged at the pupil position of the objective lens. The phase plate 1 is composed of a pair of joint components 1a and 1b, and on the joint surfaces of both joint components 1a and 1b, as shown in FIG. The phase film 3 that modulates the phase of the next light by 90 ° is formed. The outer surfaces of both joint components 1a and 1b which come into contact with air are formed in a flat shape, but the joint surfaces of both joint components 1a and 1b are curved with a radius of curvature R.

When both the joint parts 1a and 1b are formed by parallel plane plates as in the conventional example, the 0th order light from the sample surface is specularly reflected by the dimming region 2 of the phase plate 1 and the reflected light is obtained. Was reflected again by the lens group and the cover glass CG closer to the sample surface than the phase plate 1 and reached the image forming surface to reduce the contrast. However, in this embodiment, since the joining surface provided with the dimming region 2 and the phase film 3 has a curvature, the 0th-order light from the sample surface is reflected when the dimming region 2 of the phase plate 1 is reflected. Even if the angle becomes large and it is reflected again by the lens group on the sample surface side, it does not enter the visual field of the image forming surface. Therefore, the reduction in contrast can be minimized. Further, since the curvature of the joint surfaces of both joint components 1a and 1b is only changed, the amount of aberration generated by the phase plate is not different from that of the conventional example. Therefore, it is not necessary to make any other changes, and the flare can be reduced only by changing the phase plate 1.

Although it is desirable to use the same glass material for both the joining components 1a and 1b of the phase plate 1, glass materials having a difference in refractive index of 0.1 or less have the same effect. That is, if the joint components 1a and 1b having substantially the same refractive index, the entire phase plate 1 is simply a plane parallel plate. Therefore, the radius of curvature R of the cemented surface does not affect the aberration, and only the imaging performance can be improved.

The radius of curvature R of the joint surfaces of the joint parts 1a and 1b is determined only by the allowable flare amount. The double-reflection surface that most affects flare on the image plane is a surface with high reflectance, that is, the cover glass CG without an antireflection film and the dimming region 2 with a metal film deposited. After the ray a with the maximum numerical aperture of the maximum real field of the sample passes through the phase plate,
Letting L be the distance between the point P, which intersects the optical axis z when traveling only in air, and the pupil position of the objective lens, and let n be the refractive index of the phase plate, it is possible to form so that | R | ≦ n × L. For example, the light ray reflected by the dimming region 2 is reflected more outward than the incident light ray with respect to the optical axis z, which is preferable. Considering that the lens group between the sample surface and the phase plate actually has an aberration, | R | ≦ L exhibits the effect.

FIG. 3 shows a concrete example of an objective lens for a phase contrast microscope according to the present invention. This objective lens is a plan objective for phase difference, magnification: β = 20x, numerical aperture: NA =.
0.5, working distance: WD = 2.1 mm,
Focal length: f = 10.0 mm. Table 1 shows the lens specifications of this objective lens. In the table, the first column is the lens surface number from the sample side, the second column r is the radius of curvature of each lens surface, the third column d is the distance between the lens surfaces, and the fourth column n.
_d is the refractive index of each lens with respect to the d-line, and the fifth column ν _d is the Abbe number with respect to the d-line of each lens. This objective lens has an infinite design and is used in combination with the imaging lens shown in Table 2.

[0010]

[Table 1]

[0011]

[Table 2]

In Table 1, the lens surfaces 11, 12 and 13
Is a phase plate 1, and the lens surface 12 is a cemented surface. The amount of flare light when the radius of curvature R of this joint surface was variously changed was calculated. Dimming area 2 in the calculation
Only flare light reflected by the cover glass CG and reaching the image plane was considered. When the radius of curvature R of the cemented surface is flat as in the conventional example, that is, when R = ∞, the ratio of flare light to the amount of light reaching the imaging surface was 3.2%, but R = L =
When it is 86.3 mm, the ratio of flare light is 1.2.
%, That is, decreased to 3/8 of the conventional example. Also R
= L / 2 = 43.15 mm, the ratio of flare light is 0.4%, that is, it is reduced to 1/8 of the conventional example, and when the objective lens according to the present invention is used, the flare light is obviously reduced. Was confirmed.

[0013]

According to the present invention, it is possible to obtain a high contrast phase difference microscope objective lens with less flare without newly generating aberration due to the phase plate.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention.

FIG. 2 is a view taken along the line AA in FIG.

FIG. 3 is a lens configuration diagram showing a specific example of the present invention.

[Explanation of symbols]

1 ... Phase plate 1a, 1b ... Joining member 2 ... Dimming area 3 ... Phase film CG ... Cover glass

Claims (3)

[Claims] 1. A dimming region for reducing the transmittance of 0th-order light and a phase film for modulating the phase of the 0th-order light by 90 ° on the joint surface of a pair of cemented components having a flat lens surface in contact with air. An objective lens for a phase contrast microscope having a phase plate provided with, wherein the joint surfaces of the pair of joint components are formed to have a radius of curvature. 2. A radius of curvature of the cemented surface is R, and a ray having a maximum numerical aperture in the maximum real field of view of the sample intersects the optical axis when traveling only in the air after passing through the phase plate, and the objective lens The objective lens for a phase contrast microscope according to claim 1, which is formed so that | R | ≦ L, where L is a distance from a pupil position. 3. The objective lens for a phase contrast microscope according to claim 1, wherein the pair of bonded parts are made of the same glass material or made of a glass material having a refractive index difference of 0.1 or less.