Optical: systems and elements – Compound lens system – Microscope
Reexamination Certificate
2002-04-01
2003-11-04
Robinson, Mark A. (Department: 2872)
Optical: systems and elements
Compound lens system
Microscope
C359S232000, C359S739000
Reexamination Certificate
active
06643061
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a transmitted-illumination apparatus applicable to various types of microscopes.
There are conventional methods, such as a phase-contrast observation method, a differential-interference observation method, a modulation-contrast method and an oblique illumination method, for visualizing various colorless transparent phase-samples and observing them.
In the phase-contract observation method, a ring slit is provided at a position of a pupil of an illumination optical system of a microscope. A phase film having a conjugate shape with the ring slit is disposed at a pupil of a focusing optical system provided at a position conjugate with the ring slit.
An advantage of this observation method resides in that observation images with clear contrast can be obtained with high detection sensitivity, even for samples with a small difference in refractive index between structures, or minute granular structures of cells. On the other hand, a disadvantage of this observation method resides in that a phenomenon called “halo”, in which an end portion of a structure of a sample looks shining in white, occurs and this makes it difficult to determine the contour of a structure. In addition, it is necessary that the ring slit provided in the illumination optical system and the phase film disposed at the pupil plane of the observation optical system be made to coincide by projection, thereby improving the aberration performance of the pupil from the ring slit to the phase film plane. In the phase-contrast observation method, there arises no problem with the observation at a high magnification, but the aberration performance of the pupil for the observation at a low magnification or a very low magnification cannot satisfactorily be corrected. In fact, the phase-contrast observation method is applicable to objective lenses with a magnification of ×4 at most.
In the differential-interference observation method, two polarized light components crossing at right angles, which are produced by a birefringent crystal, are radiated on a sample plane with a slight displacement, and these light components are made to interfere with each other, thereby observing a minute structure of the sample. An advantage of this observation method resides in that stereoscopic observation with very high contrast can be performed. On the other hand, a disadvantage of this observation method is that the use of the birefringent crystal increases costs and because of use of polarized light, no exact observation image can be obtained in a case of a material which affects the polarized state. For example, a plastic Petri dish is unsuitable for the differential-interference observation. The reason is that polarized light is disturbed by birefringence of plastic material. In addition, the polarization state is disturbed by a distortion of a lens or an objective lens in the illumination optical system, a purpose-specific objective lens, etc. is needed. Moreover, since two light beams are subjected to interference, a lens capable of actual observation needs to have a magnification of ×4 or more, and this is not suitable for observation with a low magnification or a vary low magnification.
In the modulation-contrast observation method, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 51-128548, a slit is provided at a position of a pupil of an illumination optical system of a microscope, and a plurality of regions with different transmittances are provided at a position of a pupil of a focusing optical system. Normally, an absorption film having a proper transmittance is disposed at a region conjugate with the slit. A transmission region is provided on one side adjacent to the absorption film, and a light-shield region is provided on the other side. On a pupil plane, light transmission regions vary depending on a magnitude of refraction due to a structure in a sample, and a transmittance varies accordingly. Thus, a stereoscopic image with white/black shading can be obtained. An advantage of this observation method resides in that a stereoscopic image with shading on a phase object can be obtained with a relatively inexpensive structure. Since this method is free from halo, which occurs in the above-mentioned phase-contrast observation method, the contour of a structure can be easily observed and this method is suitable for manipulation of a cell, etc. On the other hand, a disadvantage of this observation method resides in that the detection sensitivity is lower than in the phase-contrast observation method and it is difficult to determine a minute structure. Moreover, a difficult operation for regulating the directions of the slit and absorption film needs to be performed each time the objective lens is exchanged. Besides, in order to project the slit onto the absorption film of the observation optical system, it is necessary to improve the aberration of the optical system for projecting the pupil, like the phase-contrast observation method. Because of this, with the objective lens of a low magnification or a very low magnification, the pupil aberration cannot satisfactorily be corrected and proper observation cannot be performed.
There are an oblique illumination method and a dark-field illumination method as illumination methods for visualizing phase-samples.
FIGS. 1A
to
1
D are schematic views of condenser lenses in general oblique illumination methods. In these figures, numeral
1
denotes an aperture stop;
2
a
,
2
b
lens groups; and
3
a sample. The aperture stop
1
limits the aperture for illumination and has a variable circular aperture. The aperture stop
1
moves in a plane perpendicular to an illumination optical axis O, thereby controlling the angle of illumination onto the sample
3
. Specifically,
FIG. 1B
shows the state of the pupil in a case where the aperture stop
1
in the state shown in
FIG. 1A
has been moved and reduced.
FIG. 1C
shows the state of the pupil in a case where the aperture stop
1
has been further reduced.
FIG. 1D
shows the state of the pupil in a case where the aperture stop
1
has been shifted while being opened.
FIG. 2A
is a schematic view of a condenser lens in a general dark-field illumination method. In the conventional dark-field illumination method, as shown in the figure, a stop
1
a
, which has an inside portion shut off and has an outside annular portion provided with a slit, is disposed near a location where an aperture stop is disposed. As is shown in
FIG. 2B
, the stop
1
a
has a central light-shield region
1
b
. The region
1
b
prevents illumination light from directly entering an objective lens. In addition, scattered light from the sample
3
is observed to realize dark-field observation. In this case, the shape of the stop
1
a
is selected in accordance with the numerical aperture of the objective lens, whereby dark-field observation can be made using various objective lenses.
As regards observation using microscopes, not only micro-regions but also macro-regions need to be observed. There are cases where the use of an objective lens with a magnification of ×1, an objective lens with a very low magnification of ×0.5, etc. is desired. In general, a stereomicroscope is used for observing such macro-regions. The stereomicroscope is advantageous in that the cost is low, the operability is high and stereoscopic observation can be performed. In addition, as regards illumination methods, there are means, such as dark-field illumination, bright-field illumination and oblique illumination, for visualizing transparent samples such as phase samples.
Jpn. Pat. Appln. KOKAI Publication No. 4-318804 discloses a transmission-illumination apparatus for a stereomicroscope, which permits oblique illumination.
FIG. 3A
shows the transmission-illumination apparatus disclosed in this publication. As is shown in
FIG. 3A
, this apparatus is constructed such that light from a light source
5
is guided to a mirror
8
via a collector lens
6
and a frosted glass
7
, and a light beam reflected b
Kawasaki Kenji
Osa Kazuhiko
Sukekawa Minoru
Frishauf Holtz Goodman & Chick P.C.
Olympus Optical Co,. Ltd.
Robinson Mark A.
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