Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2003-05-08
2004-11-09
Schwartz, Jordan M. (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S744000, C359S380000
Reexamination Certificate
active
06816321
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims priority of the German patent application 102 22 041.7 filed May 10, 2002, which is incorporated by reference herein.
1. Field of the Invention
The invention concerns an afocal zoom for use in microscopes having a tube lens, the zoom comprising four successive optical assemblies when viewed from the object end, the first assembly having a positive focal length, the second assembly a negative focal length, the third assembly a positive focal length, and the fourth assembly a negative focal length, and the first and the fourth assembly being arranged in stationary fashion and the second and the third assembly being arranged movably for modifying the magnification of the zoom, the zoom magnification decreasing with increasing distance between the second and the third assembly. The invention furthermore concerns a microscope as well as a stereomicroscope having such an afocal zoom.
2. Description of the Related Art
Microscopes, in particular stereomicroscopes, having an afocal zoom of the aforesaid kind are used wherever high specimen magnification is required, for example in technology enterprises for the manipulation and inspection of small objects, e.g. semiconductor features or micromechanical objects; in research institutions in the biological sciences and materials science; and, for example, for the examination and manipulation of cells or even for surgical purposes. As miniaturization continues and as ever-smaller specimens are being investigated, not only do the requirements concerning the resolution of such microscopes increase, but the size of the field of view at low magnification (for rapid positioning of specimens and for an improved overview during inspections) also becomes more important.
In order to increase a microscope's magnification and allow it to be modified steplessly over a certain range, the microscope is equipped with a zoom. An afocal zoom images an object at infinity in an image located at infinity. Designating the angle with respect to the optical axis at which an object point appears at infinity as wE, and the emergence angle (after passing through the zoom) at which the image point appears at infinity as wA, the magnification of the zoom is then VZO=tan(wA)/tan(wE). The zoom system allows magnification to be varied without changing the location of the object or the image. The ratio between maximum and minimum zoom magnification is called the “zoom factor” z.
FIG. 1
shows an afocal zoom
1
constructed in accordance with the preamble of Claim
1
. A zoom construction of this kind is known, for example, from “Optical Designs for Stereomicroscopes,” K. -P. Zimmer, in International Optical Design Conference 1998, Proceedings of SPIE, Vol. 3482, pp. 690-697 (1998), or from U.S. Pat. No. 6,320,702. The known zoom type comprises, viewed from the object, four optical assemblies G
1
, G
2
, G
3
, and G
4
, groups G
1
and G
4
being arranged in stationary fashion. Group G
1
possesses a positive focal length f
1
, group G
2
a negative focal length f
2
, group G
3
again a positive focal length f
3
, and the fourth group G
4
once again a negative focal length f
4
. To modify the magnification of the zoom, the movably arranged groups G
2
and G
3
are displaced.
FIG. 1
a
) indicates the highest-magnification position, and
FIG. 1
b
) the lowest-magnification position. The change in the position of assemblies G
2
and G
3
is accomplished, under the control of cams, along optical axis
2
. The Wüllner equations known from the literature can be used to calculate the corresponding distances—i.e. distance D
12
between assemblies G
1
and G
2
, distance D
23
between assemblies G
2
and G
3
, and distance D
34
between assemblies G
3
and G
4
—on the basis of a known distance between the focal points of groups G
1
and G
4
, the known focal lengths f
2
and f
3
, and a selected magnification (of groups G
2
and G
3
).
As depicted in
FIG. 1
, D
23
is minimal at the greatest magnification and increases from there with decreasing zoom magnification, so that D
12
and D
34
are minimal at the lowest zoom magnification. The zoom factor of a system of this kind is limited only by the fact that assemblies G
2
and G
3
at maximum magnification, and assemblies G
1
and G
2
as well as G
3
and G
4
at minimum magnification, must not interpenetrate.
ENP designates the diameter of the entrance pupil of zoom
1
at the greatest magnification (
FIG. 1
a
)). Diameter EP of the entry pupil of the zoom is maximal at the greatest zoom magnification. Entrance field angle wE of the zoom designates the visual angle at which an object appears at infinity. This angle becomes minimal at the weakest zoom magnification and assumes a value w
1
, as is evident from
FIG. 1
b
). Overall length L of the zoom corresponds to the distance between the outer vertices of assemblies G
1
and G
4
.
FIG. 2
is a sketch of a microscope having an afocal zoom
1
. An object
9
is arranged at the anterior focal point of objective
10
, and is imaged thereby at infinity. The downstream afocal zoom
1
modifies the magnification within a selectable range, and once again images the object at infinity. Arranged behind zoom
1
is a tube lens
11
which generates an intermediate image
12
that in turn is visually observed through an eyepiece
13
by eye
17
. EP designates the diameter of the entrance pupil of zoom
1
. AP designates the diameter of the exit pupil of the microscope after eyepiece
13
. It is known that the resolution of the microscope depends on numerical aperture nA of objective
10
, which is defined as the sine of half the angular aperture &agr; of the cone having its vertex at the center of the object and is limited by entrance pupil EP. Well-corrected optical systems that satisfy the sine condition are known to be governed by the equation EP=2×fO nA, where fO refers to the focal length of objective
10
. For a wavelength &lgr;=550 nm, the rule of thumb for calculating the resolution capability is 3000×nA (in line pairs per millimeter). Since the numerical aperture increases with the diameter of the entrance pupil, it is obvious that a large diameter EP is needed in order to achieve high resolution.
FIG. 3
shows the schematic construction of a stereomicroscope of the telescopic type. The stereomicroscope allows the viewer to obtain a three-dimensional impression of object
9
being viewed. For that purpose, object
9
, which is located at the anterior focal point of objective
10
, is imaged through two separate observation channels. The two observation channels
15
L and
15
R are of identical construction and each contain a zoom system
1
L,
1
R, a tube lens
11
L,
11
R, and a respective eyepiece
13
L and
13
R. Image erection systems
16
L,
16
R arranged behind tube lenses
11
L,
11
R provide right-reading erect intermediate images
12
L and
12
R which are visually viewed by a pair of eyes
17
L and
17
R using the pair of identical eyepieces
13
L,
13
R. The two zoom systems
1
L and
1
R selectably modify the magnification, but identically for the right and the left channel.
The two intermediate images
12
L and
12
R are different images of object
9
, since object
9
is viewed at angle wL in left channel
15
L and at angle wR in right channel
15
R. This makes possible stereoscopic viewing of object
9
, just as an object is viewed by the pair of eyes. The two different images are processed in the brain to yield a three-dimensional image.
EP once again designates the diameter of the entrance pupil of the zoom, EP being identical for the two identically adjustable zooms
1
L and
1
R. uL and uR designate half the angular aperture of the cone, with vertex at the center of the object, that is limited by the entrance pupil. uL and uR are identical in size, since the microscope is symmetrical with respect to axis
14
of objective
10
. uL and uR can consequently both be designated u. Since wR and wL are not large, the relevant equation (by analogy with the microscope
Rottermann Ruedi
Zimmer Klaus-Peter
Hodgson & Russ LLP
Leica Microsystems (Schweiz ) AG
Schwartz Jordan M.
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