Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2000-10-19
2002-01-01
Mai, Huy (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S677000
Reexamination Certificate
active
06335833
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to a zoom lens system to be used in stereoscopic microscopes, and more specifically an afocal zoom lens system which has a high vari-focal ratio and favorable optical performance.
b) Description of the Related Art
A stereoscopic microscope is characterized in that it has a working distance which is much longer than that of an ordinary microscope and that it enables stereoscopic observation, whereby it is used for observing various specimens by utilizing these characteristic.
Currently, a stereoscopic microscope which has a high zoom ratio is required for stereoscopic observation. In other words, a stereoscopic microscope which has a high zoom ratio and excellent aberration correcting performance is effective for assembling parts of electronic circuits as well as shape observation and micrographic recording of these parts, and cell cultivation, egg selection and morphological observation in the biological field.
Stereoscopic microscopes are classified into Greenough type and Galilean type: the latter being suited for use as a stereoscopic microscope having a high zoom ratios. As shown in
FIG. 1
, a Galilean type stereoscopic microscope consists or, in order from a side of an object
1
, an objective lens
2
, afocal zoom lens systems
3
, imaging lens systems
4
and eyepieces
6
. As apparent from
FIG. 1
, optical systems on and after the afocal zoom lens systems are arranged in parallel with an optical axis of the objective lens
2
and eccentrically from the optical axis in the Galilean type stereoscopic microscope. Further, optical axes X
1
and X
2
of the afocal zoom lens systems
3
which correspond to left and right eyes extend toward the object so as to pass through the objective lens and are coincident with each other on a surface of the object
1
. An angle &thgr; formed between the two optical axis X
1
and X
2
corresponding to the left and right eyes is referred to as an internal inclination angle.
When zoom lens systems are configured as afocal zoom lens systems as in the stereoscopic microscope described above, it is possible to change a magnification through conversion of the objective lens, and to interpose a unit such as an illuminating optical system between the zoom lens systems and the imaging lens systems for coping with observation in various modes.
Further, the Greenough type stereoscopic microscope consists, in order from the object side, of objective lenses
2
, zoom lens systems
3
and eyepieces
6
as shown in FIG.
2
. Differently from zoom lens systems of the Galilean type stereoscopic microscope, the left and right zoom lens systems of the Greenough type stereoscopic microscope are disposed so as to have optical axes X
1
and X
2
which intersect at an angle. The Greenough type stereoscopic microscope is inferior from a viewpoint of systemization though the Greenough type has a merit that it can be manufactured at a lower cost and more compact than the Galilean type stereoscopic microscope.
As conventional zoom lens system for stereoscopic microscopes, there are known optical systems disclosed by Japanese Patents Kokoku Publication No. Sho 55-41402, Kokoku Publication No. Sho 55-40849, Kokoku Publication No. Sho 53-9094 and Kokoku Publication No. Sho 51-13663. However, these conventional examples have zoom ratios which are not sufficiently high.
Further, an optical system disclosed by Japanese Patent Kokoku Publication No. Hei 6-77104 is known as another conventional example. This conventional example uses afocal zoom lens systems having a zoom ratio of 8.5 which is higher than those of the other conventional examples mentioned above, but does not correct chromatic aberration sufficiently favorably at high magnifications and cannot satisfy current requirements for stereoscopic microscopes.
Furthermore, a perfocality deviation occurs when a temperature changes in an environment of a stereoscopic microscope. In such a case, this deviation is compensated by changing a working distance between an objective lens and an object.
FIG. 3A
shows a conceptional diagram of a stereoscopic microscope which is set at ordinary temperature and
FIG. 3B
shows a conceptional diagram of a stereoscopic microscope which is set at an elevated temperature.
In the stereoscopic microscope set at ordinary temperature shown in
FIG. 3A
, optical axes X
1
and X
2
for left and right eyes pass through an objective lens
2
and coincide with each other on an object surface
1
. When the temperature changes and a working distance is changed to compensate for a perfocality deviation as shown in
FIG. 3B
, however, centers of optical axes for the left and right eyes are located at
6
and
7
on the object surface in
FIG. 3B
, thereby being not coincident with each other on the object surface. Accordingly, left and right images to be observed are shifted in directions toward the afocal zoom lens systems which are eccentric from an optical axis of the objective lens. When it is desired to observe a stereoscopic image of an object which has a fine structure, it is difficult to form a stereoscopic image by fusing the left and right images which are shifted leftward and rightward as described above. Not only the Galilean type stereoscopic microscope but also the Greenough type stereoscopic microscope has such a defect.
When a stereoscopic microscope is used in an environment which is the same as that selected for its assembly and adjustment, it is free from the problem of the perfocality deviation caused by the environmental change described above. The perfocality deviation due to a temperature change is caused by a refractive index change and linear expansion of a glass material as well as deformation of a lens barrel. Further, this phenomenon occurs also in cameras and there have been proposed various means to suppress perfocality deviations due to temperature changes. In case of a camera lens system which is free from the phenomenon to shift a center of an image, it is sufficient to simply move a lens unit adopted for compensating a perfocality deviation or another means so that an object and an image surface are conjugate with each other. Furthermore, an ordinary microscope which is also free from the phenomenon to shift a center of an image is capable of compensating a perfocality deviation by changing a working distance between a specimen and an objective lens.
The shifts of images to be observed by the left and right eyes which are caused by an environmental temperature change is therefore a phenomenon peculiar to an eccentric optical system of a stereoscopic microscope. An optical system of a stereoscopic microscope which allows images to shift for a long distance has a defect that it makes a stereoscopic microscope incapable of producing stereoscopic image of a fine structure.
In an optical system of a stereoscopic microscope, afocal zoom lens systems are affected most by the perfocality deviation due to a temperature change and the perfocality deviation is more remarkable as the lens systems have a higher magnification. Speaking concretely, a dynamic environmental change at a higher magnification produces a perfocality deviation in a larger amount, and centers of the optical axes for the left and right eyes are shifted for a longer distance in proportion to the perfocality deviation amount, thereby making the lens systems unsuited for stereoscopic observation at the high magnification.
At a high zoom magnification, even a temperature change of ±20° C. from 20° C. causes shifts of images to be observed by the left and right eyes due to perfocality deviation, thereby making the lens systems unsuited to observation of cells and eggs cultivated in a thermostatic chamber kept, for example, in an environment at approximately 40° C. and observation at an atmospheric temperature of approximately 40° C. or below ice point.
Refractive indices of glass materials are changed variously even by the same temperature change. Glass materials which have extraordinary dispersive properties capa
Mai Huy
Olympus Optical Co,. Ltd.
Pillsbury & Winthrop LLP
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