Optical: systems and elements – Compound lens system – Microscope
Reexamination Certificate
1999-09-09
2002-05-07
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Compound lens system
Microscope
C359S381000, C359S388000
Reexamination Certificate
active
06384967
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an illumination apparatus for a microscope in which the diameter of an aperture diaphragm or the like is switched in association with switching of an observation method or an objective lens.
In an illumination (an incident illumination, a projection illumination) observation microscope, illumination light radiated from an illumination light source is passed through an objective lens and irradiated onto a sample. Reflection light from the sample is passed through the objective lens again so as to enter into an eyepiece lens or a television camera, thus achieving observation. In this microscope, a plurality of objective lenses are attached to a revolving nosepiece (revolver), and observation can be performed while changing the magnification by rotating the revolving nosepiece.
Recently, in many revolving nosepieces of this type, objective lenses are changed from each other by electrically rotating the revolving nosepiece. There are also microscopes in which other various operating sections are electrified in addition to the revolving nosepiece so that operation is facilitated. In particular, if the aperture diaphragm and the field diaphragm in the illumination system are set to appropriate diaphragm diameters in compliance with the objective lens and in accordance with a bright field illumination observation method or a dark field illumination observation method, the optical performance can be extracted at maximum. Therefore, there has been provided a microscope which changes the diaphragm diameter under electric control in association with the revolving nosepiece.
For example, the aperture diaphragm and the field diaphragm in the bright field illumination observation takes various optimum diameters depending on the magnifications of the objective lenses and the pupil diameter. Therefore, control is performed so as to change the diaphragm diameters every time when the revolving nosepiece is switched. In addition, the aperture diaphragm and the field diaphragm in the dark field illumination observation are basically set to the maximum diameters, i.e., released in order to maximum use of the illumination light. These diaphragms are automatically switched to the maximum diameters when the dark field illumination is carried out.
FIGS. 15A and 15B
are partial cross-sectional views showing a revolving nosepiece and an objective lens in the dark field illumination described above.
FIG. 15A
shows a light passage of illumination light for normal dark field illumination. The revolving nosepiece
301
is equipped with an objective lens
303
having a ring-like dark field illumination light passage
302
. When dark field illumination light
305
enters into a dark field illumination light passage
304
, this light
305
passes through the dark field illumination light passage
302
of the objective lens
303
and is irradiated onto a sample
306
. At this time, regular reflection light from the sample
306
is reflected at the same angle as the incident angle to the sample
306
, and therefore does not enter into the observation light passage
307
of the objective lens
303
. Accordingly, only scattered light from the sample
306
enters into the observation light passage
307
, so that an effective dark field illumination observation method can be practiced by detecting feeble scattered light.
However, a problem of stray light occurs when the revolving nosepiece
301
is rotated to change the objective lens
303
.
FIG. 15B
shows a light passage for illumination light halfway while the objective lens
303
is changed with another one. That is, the revolving nosepiece
301
starts rotating to change the objective lens
303
, and the objective lens
303
is slightly inclined and deviates from its original optical axis. In this situation, a part (in form of a crescent moon) of the ring-like dark field illumination light
305
comes out of the range of the dark field illumination light passage
302
of the objective lens
303
, and passes through the observation light passage
308
of the objective lens
303
, to be irradiated onto the sample
306
. Further, the regular reflection light from the sample
306
enters into the observation light passage
307
of the revolving nosepiece
301
while maintaining its large amount, so that unnecessary excessive light beams as stray light enter.
Normally, dark field observation is carried out by detecting feeble scattered light, so the light amount of the illumination light is large while the observation light is weak. Therefore, if a large amount of stray light enters into the observation light passages
307
and
308
even at an instant halfway while changing the objective lens
303
, an observer takes a risk for eyes of his or her own and feels dazzled in case of eye observation, and bad influences may be effected on the image pick-up element in case of television observation.
With respect to the problem as described above, for example, a conventional apparatus adopts a method of inserting and then pulling out a special shutter at the same time when an objective lens is changed. However, in this case, it is necessary to use a special shutter mechanism and other components which are disadvantageous in view of costs.
In contrast, in place of using such a shutter, there is a method of electrically reducing the field diaphragm to the minimum diameter by means of an iris diaphragm (a plurality of diaphragm wings) to prevent stray light at the same time when changing an objective lens. In this case, however, thin iris diaphragm must be opened and closed every time when an objective is changed, so that the durability of the iris diaphragm may become unreliable. In addition, the speed at which the iris diaphragm is limited by the unreliableness of durability caused due to opening and closing of the iris diaphragm, and as a result, it takes a very long time to change an objective lens.
As a known example, Japanese Patent Application KOKAI Publication No. 6-337359 discloses that the power source of an illumination light source is shut off to prevent stray light when changing an objective lens. Further, Japanese Patent Application KOKAI Publication No. 7-209584 discloses that a revolving nosepiece is rotated after the light amount drops sufficiently when changing an objective lens.
Although this technique brings about an effect that a large amount of stray light is prevented from entering into observation light passages, the illumination light source is turned on and off so frequently that the lifetime of the illumination light source is shortened as a result. For example, in case of a halogen lamp generally used as an illumination light source, it has been known that the lifetime is shortened if it is repeatedly turned on and off. In addition, many light sources cannot be turned on and off simply (e.g., ark light sources such as mercury lamps and the like). If one of those light sources is used, stray light cannot be prevented from entering, by turning on and off the lamps. Further, each of the techniques described above adds another operation to various switching operations, so that only a low efficiency can be attained in view of the electric power and the durability.
There is another known technique in which a light reduction unit based on adjustment of the brightness of a light source or based on switching of an ND filter (Neutral density filter) is electrically controlled in accordance with the magnification and the transmittance of the objective lens, thereby to minimize the change of the brightness caused by switching (or changing) an objective lens. These functions are optionally and selectively equipped in compliance with the use frequency and the price range.
Japanese Patent Application KOKAI Publication No. 9-21957 discloses a microscope in which the aperture diaphragm and the light adjustment unit (or ND unit) are controlled to attain optimum conditions on the basis of various original data concerning objective lenses. Objective lenses have respectively different transmittance depen
Kubota Shunichi
Matsushita Shinji
Sukekawa Minoru
Watanabe Akira
Olympus Optical Co,. Ltd.
Robinson Mark A.
Spyrou Cassandra
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