Patent Description:
For use in a microscope, optical systems are known, which provide a zoom function enabling an object to be imaged onto an image plane with continuously variable magnification. For this purpose, such an optical system includes one or more lens groups which can be moved along the optical axis for zooming between a short focal length extremity and a long focal length extremity. Usually, the optical system includes a cam mechanism or the like in order to move the zoom lens groups in an interdependent manner.

A microscope including an optical zoom system as described above further comprises a focusing device which is designed to focus the object onto the image plane for any zoom setting, i.e. for any positioning of the zoom lens groups along the optical axis. Usually, such a focusing device is configured to vary an axial distance from an object plane, on which the object is located, to the image plane. For this purpose, the focusing device may move the optical system relative to a microscope stage on which the object is arranged, or vice versa.

Providing the microscope with such a focusing device involves considerable effort in terms of the components which have to be provided in order to achieve the relative movement between the optical system and the microscope stage. Further, as the focusing device has to be operated by the user, the focusing operation is cumbersome and time-consuming.

Document <CIT> discloses an optical system which includes, starting from the object side, an objective of fixed focal length, an afocal Galilean telescope system, an afocal zoom system and a tube lens. The afocal zoom system which is arranged between the Galilean telescope system and the tube lens comprises in total five lens groups with two outer groups and three inner groups. Both outer lens groups have positive power.

Document <CIT> discloses a telecentric modular zoom system which comprises in total four lens groups. A first lens group and a second lens group have positive power, and a fourth lens group is movable along the optical axis thereof.

Therefore, it is an object of the present invention to provide an optical system for imaging an object onto an image plane of a microscope, said optical system enabling a focusing operation in a convenient and precise manner.

In order to achieve the afore-mentioned object, an optical system for imaging an object onto an image plane of a microscope according to claim <NUM> is provided, the optical system comprising a first lens group and a fourth lens group which are stationary, and a second lens group and a third lens group which are independently movable along an optical axis of the optical system for focusing the object onto the image plane while zooming between a short focal length extremity and a long focal length extremity.

The optical system as described above enables continuously zooming, i.e. continuously varying a total focal length of the optical system between the short focal length extremity and the long focal length extremity, and at the same time continuously focusing, i.e. continuously varying a distance from the object plane to the image plane.

A coupled zooming and focusing control is achieved by independently moving the second lens group and the third lens group while the first lens group and the fourth lens group remain stationary. Thus, it is possible to simultaneously adjust the magnification, based on which the object is imaged onto the image plane of the microscope, and the axial distance from the object plane, on which the object is arranged, to the image plane. As a result, the optical system enables the user of the microscope to realize the desired zoom and focus adjustments in a convenient and precise manner.

In this respect, it is to be noted that the afore-mentioned image plane is meant to be any plane on which an image is created by the optical system. In particular, such an image plane may comprise a plane on which a sensor as for instance a digital camera is located, and a plane on which an intermediate image is generated.

The first lens group having negative power, the second lens group having positive power, the third lens group having positive power and the fourth lens group having negative power are arranged in this order from an object side. According to this embodiment, the stationary lens groups are formed the outer lens groups of the optical system, i.e. by the first and fourth lens groups facing towards the object side and the image side, respectively. Thus, a compact design of the optical system is achieved.

In a preferred embodiment, the optical system is configured to be telecentric on an object side and telecentric on an image side. Such a double-sided telecentric configuration enables the object to be imaged with high image quality.

In a preferred embodiment, the short focal length extremity and the long focal length extremity define a zoom range from Z1=<NUM> to Z2=<NUM>. A limitation of the zoom range to the afore-mentioned values Z1 and Z2 allows a design of the optical system in which the moving distances of the second lens group and the third lens group when performing the coupled zooming and focusing operation do not become too large. Thus, a compact design of the optical system is achieved.

Preferably, memory means are provided for storing information assigning each combination of zoom setting and focus setting to a corresponding lens group position along the optical axis for each of the second and third lens groups. Storing the zoom and focus information enables the optical system to be controlled in a simple and precise manner.

In a preferred embodiment, the optical system comprises an optical element for coaxial light coupling. Such an optical element may be used for coupling illumination light emitted by a light source of the microscope into the optical system. Thus, the optical system can be used for both illuminating and imaging the object.

In a preferred embodiment, the optical element is arranged in a segment of the optical system where an angular characteristic of light passing the optical system is the same for the whole range of zoom and focus positions of the second lens group and the third lens group. In case that, for instance, an illumination path is coupled into the optical system by means of the afore-mentioned optical element, the entire zoom range, i.e. all zoom positions of the second and third lens groups, can be supplied with light passing the optical system from the object plane to the image plane without having to perform a corresponding zoom operation on the illumination light path which is coupled into the optical system by the optical element.

Preferably, the optical element is arranged in the fourth lens group.

In case that the optical element is arranged in the fourth lens group, the latter preferably comprises a first sub-lens group having negative power and a second sub-lens group having positive power arranged in this order from the object side, wherein the optical element is arranged between the first sub-lens group and the second sub-lens group.

According to another aspect, a method is provided for imaging an object onto an image plane of a microscope, comprising the steps of holding a first lens group and a fourth lens group stationary during imaging of the object; and moving a second lens group and a third lens group independently along an optical axis for focusing the object onto the image plane while zooming between a short focal length extremity and a long focal length extremity.

According to another aspect, a microscope is provided comprising an image plane and an optical system as described above.

Hereinafter, preferred embodiments are described with reference to the drawings in which:.

<FIG> is a lens diagram showing an optical system <NUM> which may be included into a microscope for imaging an object onto an image plane IP. The image plane IP may be a plane in which an image sensor of the microscope is arranged. Alternatively, the image plane IP may be a plane in which an intermediate image is created.

<FIG> shows in its upper half the configuration of the optical system <NUM> at a short focal length extremity, i.e. in a setting in which a magnification provided by the optical system <NUM> is maximal (Vmax in <FIG>). Correspondingly, <FIG> shows in its lower half the optical system <NUM> at a long focal length extremity, i.e. in a setting in which the magnification provided by the optical system <NUM> is minimal (Vmin in <FIG>). Further, <FIG> shows for each of the focal length extremities two focusing states, namely a first focusing state in which a distance from an object plane OP1 to the image plane IP along an optical axis O is minimal, and a second state, in which a distance from an object plane OP2 to the image plane IP along the optical axis O is maximal. The distance between the object plane OP1 and the object plane OP2 defines a focus range FR.

The optical system <NUM> comprises a first lens group L1 having negative power, a second lens group L2 having positive power, a third lens group L3 having positive power and a fourth lens group L4 having negative power, the lens group L1 to L4 being arranged in this order from the image plane OP1, OP2 to the image plane IP. The first lens group L1 facing towards the object plane OP1, OP2 and the fourth lens group L4 facing to the image plane IP are stationary. In other words, upon focusing and zooming, the two outer lens groups L1, L4 of the optical system <NUM> remain unchanged in their positions along the optical axis O. In contrast, both inner lens groups L2, L3 of the optical system <NUM> are independently moved along the optical axis O for focusing the object onto the image plane IP while zooming between the long focal length extremity, i.e. Vmin, and the short focal length extremity, i.e. Vmax.

Specifically, both the second lens group L2 and the third lens group L3 are moved from the object plane OP1, OP2 to the image plane IP while zooming between the long focal length extremity and the short focal length extremity. Further, the second lens group is moved towards the object plane OP1, OP2, and the third lens group L3 is moved towards the image plane IP when the distance from the object plane to the image plane IP is increased, i.e. when the object plane is moved from OP1 to OP2. This focusing movement of the second lens group L2 and the third lens group L3 applies for both the long focal length extremity and the short focal length extremity.

<FIG> shows for each zoom and focus setting two beam paths associated with object points Q1, Q2 which are spatially separated in the respective object plane OP1, OP2. The object point Q1 is imaged by the optical system <NUM> into an image point R1. Likewise, the object point Q2 is imaged by the optical system <NUM> into an image point R2. As illustrated by the respective beam parts, the optical system <NUM> may be configured to be telecentric both on the object side and on the image side.

According to the embodiment shown in <FIG>, the short focal length extremity and the long focal length extremity may define a zoom range from Z1=<NUM> to Z2=<NUM>. Needless to say that the embodiment is not limited to the afore-mentioned zoom range.

Each combination of zoom setting and focus setting corresponds to a combination of an associated position of the second lens group L2 and an associated position of the third lens group L3 along the optical axis O. Thus, an information assigning each combination of zoom setting and focus setting to the corresponding lens group positions of the second and third lens groups L2, L3 O may be stored beforehand so that this information can be referred to when a specific zoom setting and a specific focus setting shall be provided.

<FIG> shows a modified embodiment referring to a lens diagram which corresponds to the lens diagram of <FIG>. According to the modified embodiment shown in <FIG>, an optical system <NUM> comprises an optical element <NUM> for coaxial light coupling. Specifically, the optical element <NUM> may be configured to couple illumination light coaxially into the optical system <NUM>, the illumination light being emitted by a light source not shown in <FIG>. For this purpose, the optical element <NUM> may be formed as a beam splitter which is configured to reflect the illumination light towards the object plane OP1, OP2 and which is further configured to transmit the light passing the optical system <NUM> from the object plane OP1, OP2 to the image plane IP. The optical element <NUM> may be arranged within the fourth lens group L4, in particular between a first sub-lens group <NUM> having negative power and a second sub-lens group <NUM> having positive power. Within the fourth lens group L4, the first sub-lens group <NUM> is positioned to face the image plane OP1, OP2, and the second sub-lens group <NUM> is positioned to face the image plane IP.

Preferably, the optical element <NUM> is arranged in a segment of the optical system <NUM> where an angular characteristic of light passing through the optical system <NUM> is the same for the whole range of zoom and focus positions of the second lens group L2 and the third lens group L3. In other words, the segment of the optical system <NUM>, which preferably includes the optical element <NUM>, exhibits a constant angular characteristic with respect to the light passing the optical system <NUM> throughout the entire zoom range from the short focal length extremity to the long focal length extremity as well as throughout the entire focus range FR defined by OP1 and OP2. As the afore-mentioned angular characteristic remains unchanged while performing the coupled zoom and focus operation, the light passing the optical system <NUM> from the object plane OP1, OP2 to the image plane IP1 can be supplied to all zoom positions of the second and third lens group L2, L3 without any need to perform a corresponding zoom operation on the illumination light path which is coupled into the optical system <NUM> by means of the optical element <NUM>.

<FIG> shows an embodiment of a microscope <NUM> which may comprise the optical system <NUM> shown in <FIG>. Specifically, the microscope <NUM> includes a first magnification changing subsystem <NUM> which comprises a first digital camera <NUM> and a first optical magnification system which is formed by the optical system <NUM> as shown in <FIG>. The first digital camera <NUM> and the optical system <NUM> are aligned along a first optical axis O1.

The microscope <NUM> further comprises a second magnification changing subsystem <NUM> including a second digital camera <NUM> and a second optical magnification system <NUM>. The second digital camera <NUM> and the second optical magnification system <NUM> are aligned along a second optical axis O2.

The microscope <NUM> further comprises a controller <NUM> including a memory <NUM>. Further, the microscope <NUM> comprises a microscope stage <NUM> on which an object <NUM> is arranged. The microscope stage <NUM> is movable in a direction orthogonal to the optical axis O1 and O2 by means of a positioning device <NUM>. In particular, the controller <NUM> is configured to cause the positioning device <NUM> to laterally shift the microscope stage <NUM> such that a target region <NUM> of the object <NUM> is positioned on the optical axis O1 of the first magnification changing subsystem <NUM> or the optical axis O2 of the second magnification changing subsystem <NUM>.

Whereas the first magnification changing subsystem <NUM> comprising the optical system <NUM> may be used as an optical zoom system, the second magnification changing subsystem <NUM> may be used as a digital zoom system. For this, the second digital camera <NUM> may be provided with a digital zoom function whereas the second optical magnification system <NUM> is configured to provide a fixed magnification.

For instance, in the configuration shown in <FIG>, the second magnification changing subsystem <NUM> may be used to generate an overview image when its optical axis O2 is aligned with the target region <NUM> of the object <NUM>. As soon as the overview image has been generated, the first magnification changing subsystem <NUM> is aligned with the target region <NUM>, whereupon the optical system <NUM> is controlled to perform the combined focus and zoom operation as described above in order to adjust a desired magnification while focusing on the target region <NUM>. For this, the controller <NUM> may retrieve the information for correctly positioning the second lens group L2 and the third lens group L3 along the optical axis O1 from the memory <NUM>.

It is to be noted that the microscope <NUM> shown in <FIG> represents merely an exemplary microscope configuration which is suitable to apply the combined zooming and focusing operation provided by the optical systems <NUM>, <NUM> as shown in <FIG> and <FIG>, respectively. Thus, the optical systems <NUM>, <NUM> may be used in any other type of microscope which requires focusing and zooming.

Claim 1:
An optical system (<NUM>, <NUM>) for imaging an object (<NUM>) onto an image plane (IP) of a microscope (<NUM>), comprising in total four lens groups (L1, L2, L3, L4), wherein:
a first lens group (L1) having negative power, a second lens group (L2) having positive power, a third lens group (L3) having positive power and a fourth lens group (L4) having negative power are arranged in this order from an object side,
the first lens group (L1) and the fourth lens group (L4) are stationary, and
the second lens group (L2) and the third lens group (L3) are independently movable along an optical axis (O) of the optical system (<NUM>, <NUM>) for focusing the object (<NUM>) onto the image plane (IP) while zooming between a short focal length extremity and a long focal length extremity.