Optical: systems and elements – Compound lens system – Microscope
Reexamination Certificate
1999-02-05
2001-04-03
Nguyen, Thong (Department: 2872)
Optical: systems and elements
Compound lens system
Microscope
C359S368000, C359S385000
Reexamination Certificate
active
06212005
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microscope illumination optical system and a microscope having illumination optical system. More particularly, the present invention relates to a microscope illumination optical system capable of varying the visual field and the numerical aperture according to the magnification of a microscope objective.
2. Description of Related Art
Japanese Patent Application Unexamined Publication (KOKAI) No. 9-33820 proposes a conventional microscope illumination optical system in which three condenser lenses having different focal lengths are prepared, a condenser lens for a high magnification, a condenser lens for a low magnification, and a condenser lens for an ultra-low magnification. The three Condenser lenses perform appropriate illumination according to the magnification of a microscope objective, by switching the condenser lenses from one to another, according to the magnification of the microscope objective.
FIGS.
5
(
a
) and
5
(
b
) are ray path diagrams illustrating the conventional microscope illumination optical system. FIG.
5
(
a
) shows the arrangement of the illumination optical system in the case of a high or low magnification. FIG.
5
(
b
) shows the arrangement of the illumination optical system in the case of an ultra-low magnification. When the illumination optical system is in the position shown in FIG.
5
(
a
), light from a light source
1
passes through a first collector lens unit L
1
and a second collector lens unit L
2
. The two collector lens units L
1
and L
2
form a first image of the light source
1
. A first variable stop A is placed at the position of the first image. A light beam passing through the first variable stop A passes through a first intermediate lens unit L
3
, a second variable stop F and a second intermediate lens unit L
4
. The two intermediate lens units L
3
and L
4
form a second image of the light source
1
. Accordingly, the position of the image plane of the second image is conjugate to the first variable stop A with respect to the two intermediate lens units L
3
and L
4
. The second variable stop F is placed at the front focal point of the second intermediate lens unit L
4
. A condenser lens unit LC
1
for a high or low magnification is placed behind the second intermediate lens unit L
4
to lead a light beam from the second image of the light source
1
to a specimen plane
2
in the form of collimated light. The specimen plane
2
is conjugate to the second variable stop F with respect to the second intermediate lens unit L
4
and the condenser lens unit LC
1
for a high or low magnification.
Accordingly, when the illumination optical system is in the position for a high or low magnification (from 4× to 100× magnification) as shown in FIG.
5
(
a
), the first variable stop A is an aperture stop, and the second variable stop F is a field stop. The back focal point of a high- or low-magnification objective Ob
1
of a microscope is conjugate to the first variable stop A and the light source
1
. The whole illumination optical system acts as a Koehler illumination system. A specimen is placed in the specimen plane
2
, which is well defined, bright and free from illumination nonuniformity, and an enlarged image of the specimen is formed on an image plane
3
. To prevent occurrence of illumination nonuniformity and insufficiency of the numerical aperture, it is essential to insert a light diffusing plate (frosted plate) at a position I between the second collector lens unit L
2
and the first variable stop A.
When the illumination optical system is in the position for an ultra-low magnification (from 0.5× to 1× magnification) as shown in FIG.
5
(
b
), a condenser lens unit LC
2
is placed at a position in front of where the second image of the light source
1
is formed by the two intermediate lens units L
3
and L
4
. Condenser lens unit LC
2
, for ultra-low magnification, has a long focal length and is used in place of the condenser lens unit LC
1
for a high or low magnification. In this case, the second image of the light source
1
is formed on the specimen plane
2
, and an image of the second variable stop F is formed at infinity. Consequently, a light beam from a point in the aperture of the second variable stop F is incident on the specimen plane
2
in an afocal form. Accordingly, in this case, the first variable stop A is a field stop, and the second variable stop F is an aperture stop. The back focal point of an ultra-low magnification objective Ob
2
of the microscope is conjugate to the second variable stop F. The whole illumination optical system acts as a critical illumination system.
In the conventional microscope illumination optical system of Japanese Patent Application Unexamined Publication (KOKAI) No. 9-33820, when it is in the position for an ultra-low magnification, FIG.
5
(
b
), the specimen plane
2
and the light source
1
are conjugate to each other as stated above. Therefore, if a light diffusing plate (frosted plate) is not placed in the optical path from the light source
1
to the specimen plane
2
, the image of the light source
1
is superimposed on the specimen. Consequently, an undesirable filament image is seen. However, if a light diffusing plate is inserted at position I between the second collector lens unit L
2
and the first intermediate lens unit L
3
, an image of the light diffusing plate is formed near the specimen plane
2
. This is because the distance between the position I and the first variable stop A is short. Consequently, the roughness of the light diffusing plate is undesirably seen. In particular, when the aperture of the second variable stop F is reduced, the depth of focus deepens, and the roughness of the light diffusing plate becomes even more conspicuous. Therefore, the conventional illumination optical system becomes impractical.
Accordingly, it is necessary to blur the filament image by placing a light diffusing plate at a position II in or near the condenser lens unit LC
2
for an ultra-low magnification. However, because position II is between the second variable stop F and the specimen plane
2
, images of both the first variable stop A (field stop) and the second variable stop F (aperture stop) are blurred undesirably if a light diffusing plate is placed at the position II. Consequently, the visual field is not well defined, and the second variable stop F fails to function as an aperture stop. In ultra-low magnification observation with microscopes in particular, specimens of weak contrast are often made visible by reducing the aperture of the aperture stop to thereby create an under-numerical aperture condition. In this regard, if the second variable stop F cannot serve as an aperture stop, it becomes impossible to observe various images by adjusting the numerical aperture of the illumination system as stated above.
In view of the above-described problems associated with the prior art, the present invention provides a microscope illumination optical system for an ultra-low magnification (from 0.5× to 1× magnification) that has a field stop and an aperture stop. With the present invent even if a light source image is blurred by insertion of a light diffusing plate, the roughness of the light diffusing plate is not visible, and uniform illumination can be performed. In specimens of weak contrast, a phase distribution, can be made visible through adjustment of the numerical aperture by varying the aperture of the aperture stop.
SUMMARY OF THE INVENTION
The present invention provides a microscope illumination optical system including a light source and in order from the light source to a specimen plane: a collector lens system that forms a first image of the light source, a first variable stop placed at a position where the first image is formed, an intermediate lens system having a second variable stop therein and arranged to form an image of the first variable stop behind the intermediate lens system, and a plurality of condenser lens syste
Kajitani Kazuo
Kawasaki Kenji
Nguyen Thong
Olympus Optical Co,. Ltd.
Pillsbury & Winthrop LLP
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