Apparatus for changing illumination optics of a microscope

An apparatus for changing illumination optics is provided for use in a microscope including a plurality of illumination optics having different values of magnification. A photometric, light receiving element is disposed in a marginal area of an imaging surface of an objective lens, and an output from the photometric element is determined as the illumination optics are sequentially changed. A matching condition between the objective lens and the illumination optics is detected in accordance with the value determined, and that one of illumination optics is selected which represents the best match.

BACKGROUND OF THE INVENTION 
The invention relates to an apparatus for changing illumination optics of a 
microscope, and more particularly, to such apparatus for use with a 
microscope including a plurality of objective lenses and a plurality of 
illumination optics lenses, both having different values of magnification, 
allowing illumination optics of the microscope to be changed so as to 
match a particular one of the objective lenses disposed in an observation 
optical path. 
In a microscope of the kind described, a revolver may be disposed in an 
observation optical path to permit a plurality of objective lenses to be 
changed. An observer selects a particular one of illumination optics lens 
which matches the objective lens used, the selected illumination optics 
lens being disposed in an illumination optical path. This arrangement 
required a troublesome changing operation. 
To eliminate such difficulty, an arrangement has been proposed in which the 
objective lenses or the revolver is provided with indicator elements which 
indicates the values of the magnification of the various objective lenses 
so that the indicator elements may be detected and discriminated when 
changing the objective lenses to permit an automatic changing of 
illumination optics lens which matches therewith. However, this 
arrangement requires the provision of a separate indicator element for 
each objective lens or each objective lens position on the revolver, and 
it is also necessary to assure an accurate discrimination of a particular 
indicator element corresponding to each value of magnification. This 
presented a problem in the design of the indicator elements. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide an apparatus for changing 
illumination optics of a microscope in which a photometric light receiving 
element is disposed in a marginal area of the location of an object image 
formed by one of objective lenses in order to produce an output which is 
utilized to select a particular one of illumination optics which matches 
the objective lens. 
In accordance with the invention, a plurality of illumination optics lenses 
having different values of magnification are sequentially changed, with 
photometric outputs from the light receiving element being detected and 
stored for subsequent comparison among them to determine which photometric 
output has the maximum magnitude. The illumination optics lens which 
produced the maximum output is chosen for use with the particular 
objective lens as one which best matches the latter. Accordingly, it is 
unnecessary to provide separate indicator elements in association with 
individual objective lenses or lens positions on the revolver. The entire 
arrangement required comprises the photometric element disposed in a 
marginal area of an image field of the objective lens, a detector assembly 
which detects the output from the photometric element and stores it for 
comparison, and a drive mechanism for changing illumination optics lenses 
in response to a signal from the detector assembly. In this manner, there 
is provided an apparatus for changing illumination optics of a microscope 
which is convenient in practical use.

DESCRIPTION OF PREFERRED EMBODIMENT 
Referring to FIG. 1, there is shown a source of illumination light 11, 
which is introduced through a condenser lens 12 and a reflecting mirror 13 
to pass through illumination optics lens 1A, which is disposed in an 
illuminating optical path, for illuminating a specimen 2. An object image 
of the illuminated specimen 2 is enlarged to a given magnification by 
means of an objective lens 3A disposed in an observation optical path to 
be focussed onto an imaging surface 5 for observation through an eyepiece 
assembly, not shown. 
For the convenience of description, a plurality of objective lenses having 
different values of magnification are illustrated by a pair of objective 
lenses 3A, 3B in the present embodiment, the lens 3A being of a high 
magnification lens such as having a magnification of 100 and the lens 3B 
being a low magnification (for example, 10) lens. These objective lenses 
3A, 3B are detachably mounted on a revolver 4, and can be selectively 
disposed in the observation optical path by turning the revolver 4. 
Illumination optics lenses having different values of magnification are 
also illustrated by a pair of lenses 1A and 1B, each having a high and a 
low value of magnification. 
In accordance with the invention, at least one photometric, light receiving 
element 6 is disposed in a marginal area of the imaging surface 5, and its 
output is fed to a detector assembly 7. The detector assembly 7 may 
comprise, for example, a central processing unit including a memory and a 
comparator so that a photoelectric output from the element 6 is determined 
and stored. As the illumination optics lenses 1A, 1B are sequentially 
changed, the stored values are compared against each other to detect an 
output which exhibits the maximum value, and a corresponding signal is fed 
to a drive mechanism 8 which is utilized to change the illumination optics 
lenses. It is to be understood that the drive mechanism 8 is adapted to 
change the plurality of illumination optics lenses in a sequential manner 
when comparing outputs from the element 6. In response to the signal, the 
drive mechanism 8 drives that illumination optics lens which produced the 
maximum output into the illumination optical path. 
In operation, it is initially assumed that an observation is being made by 
using the objective lens 3A of a high magnification. When the illumination 
optics lens 1A is used to illuminate the specimen 2, an enlarged object 
image is formed by the objective lens 3A. The brightness in the marginal 
area of the image is measured, by the photometric element 6, the 
photoelectric output of which is fed to the detector assembly 7, which 
detects and stores this output. Subsequently the illumination optics lens 
is changed to the lens 1B to illuminate the specimen 2, and an object 
image thereof is formed by the objective lens 3A. The brightness of this 
object image is measured by the photometric element 6, which feeds its 
output to the detector assembly 7, which then detects and stores it. 
Both the stored values are compared against each other, with a maximum 
value being fed to the drive mechanism 8. In response to this output, the 
drive mechanism 8 brings the illumination optics lens which produced the 
maximum value, namely, the illumination optics lens 1A of the high 
magnification in the present example, into the illumination optical path. 
When the objective lens is changed to the low magnification lens 3B, both 
the illumination optics lenses 1A, 1B are sequentially brought into the 
illumination optical path to illuminate the specimen, and the outputs from 
the photometric element 6 are compared against each other (in detector 
assembly 7) to determine which illumination optics lens produces the 
maximum output, i.e., the low magnification lens 1B in the present 
example. Accordingly, this illumination optics lens is brought into the 
illumination optical path. 
In this manner, the illumination optics which best matches a particular 
objective lens used is automatically selected in accordance with the 
invention. 
Considering the reason that the described procedure provides a selection of 
optimum illumination optics, it is to be understood that when the 
objective lens used has a high magnification (lens 3A) while the 
illumination optics lens disposed in the illumination optical path has a 
low magnification (lens 1B), the field of illumination of the low 
magnification optics is greater than that of the high magnification 
optics. Accordingly, the illuminating light impinges on the objective lens 
3A over the full pupil thereof. However, since the low magnification 
optics has a numerical aperture which is substantially smaller than that 
of the high magnification optics, an insufficient amount of light is 
transmitted. Accordingly, the output from the photometric element 6 is low 
for the described combination. 
In contrast, if the low magnification objective lens 3B is used in 
combination with the high magnification illumination optics lens 1A, the 
reverse is ture. In other words, the field of illumination is reduced as 
compared with that achieved by the low magnification optics lens. 
Accordingly, an image will be formed part of which is not illuminated when 
using the low magnification lens 3B. On the other hand, the high 
magnification optics lens has a greater numerical aperture and hence 
produces high brightness. Thus, the image formed by the objective lens 3B 
will be very bright only over its central portion while the marginal 
portion will be dark, wanting in light input. Accordingly, the photometric 
element 6 again produces an output of a low magnitude. 
Finally for a combination of the high magnification lens 3A and the high 
magnification optics lens 1A or a combination of the low magnification 
objective lens 3B and low magnification optics lens 1B, both of which 
represents a best match, the field of sight of the objective lens 
coincides with the field of illumination of the illumination optics lens 
and the illumination optics lens has a numerical aperture which matches 
the numerical aperture of the objective lens, so that the entire object 
image formed by the objective lens is sufficiently bright. Consequently, 
such combination results in a maximum output from the photometric element 
6. 
These three alternative combinations are illustrated in FIGS. 2(A), (B) and 
(C) which schematically show the relationship of the field of sight, the 
field of illumination and the location of photometric elements. 
Specifically, FIG. 2(A) illustrates the use of the low magnification 
illumination optics in combination with the high magnification (100X) 
objective lens 3A. In this instance, the location of the photometric 
elements 6 which are disposed in a marginal area of the field of sight 9 
of the objective lens 3A is within the field of illumination 10, but since 
the numerical aperture of the illumination optics is less than that of the 
high magnification objective lens 3A, the entire field of illumination 
remains relatively dark, causing the photometric elements 6 to produce an 
output of a low magnitude. 
FIG. 2(B) illustrates the use of the high magnification illumination optics 
in combination with the low magnification (10X) objective lens 3B. In this 
instance, the photometric elements 6 are located outside the field of 
illumination 10, and hence the latter remains very dark. Consequently, 
they produce an output of a low magnitude. 
By contrast, FIG. 2(C) illustrates a best match between the objective lens 
and the illumination optics. In this instance, the field of illumination 
10 and the numerical aperture of the illumination optics are a good fit 
with the field of sight 9 and the numerical aperture of the objective 
lens, respectively, so that the location around the photometric elements 6 
is sufficiently bright. Hence, they produce a maximum output. 
It will be apparent from the foregoing that illumination optics which fits 
a particular objective lens used can be automatically selected by changing 
illumination optics against the objective lens used, storing individual 
outputs from the photometric element, and comparing these outputs against 
each other to determine illumination optics which produced the maximum 
output. 
While the use of four photometric elements 6 is illustrated in FIGS. 2(A) 
to (C), it is to be understood that at least one photometric element need 
only be provided in the marginal area of the image. Nevertheless, the use 
of a plurality of photometric elements 6 disposed in the manner mentioned 
permits a detection of a non-uniformity in the illumination in accordance 
with the invention. Specifically, the individual outputs from the 
photometric elements may be determined under a condition without a 
specimen, and the centering of the light source may be adjusted so that 
outputs of the individual elements are equal to each other. 
While the embodiment described represents a microscope including a pair of 
objective lenses of high and low magnifications for cooperation with a 
pair of illumination optics of high and low magnifications, it should be 
understood that the invention is not limited thereto, but is equally 
applicable to any microscope including a plurality of objective lenses 
having different values of magnification and a plurality of illumination 
optics having different values of magnification.