Optical apparatus and method for controlling optical apparatus

Abstract

To efficiently focus an objective lens regardless of the magnification of the objective lens.SOLUTION: The light sources 1 emit illumination light L1. The objective lens 5 condenses the illumination light L1 on the sample 90. The photodetectors 9 and 10 are provided at a front focus position and a rear focus position with respect to the sample 90, respectively, and detect reflection light L2 from the sample 90. The photodetector 8 detects the reflected beam L2 incident through the objective lens 5. The beam splitter 3 splits the reflection light L2 into the photodetectors 9 and 10 and the photodetector 8. The focus control unit 11 performs focusing control of the objective lens 5 with respect to the sample 90 based on the detection results of the photodetectors 9 and 10. The adjusting lens 7 is provided between the beam splitter 3 and the photodetectors 9 and 10. The lens controller 12 adjusts the optical distance between the beam splitter 3 and the photodetectors 9 and 10 to a value corresponding to the magnification of the objective lens 5.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an optical device and a method for controlling an optical device. [Background technology]

[0002] In imaging devices using optical systems such as cameras and microscopes, focus detection is widely used to automatically focus on a subject. One such focus detection method is known as front-focus / rear-focus focus detection (Patent Document 1).

[0003] In the front-focus / rear-focus method, two photodetectors are placed in front of and behind the light-receiving surface where the focal point of the secondary light from the sample is located. The intensity of the secondary light detected by the two detectors is monitored while the distance of the objective lens from the sample is changed, and the position of the objective lens when the two detectors reach a predetermined balance is detected as the position where the objective lens is focused on the sample. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-64127 Summary of the Invention [Problem to be solved by the invention]

[0005] In the front-focus / rear-focus method, the distance between the two positions of the objective lens where the light intensity detected by each of the two photodetectors is maximum is generally called the pull-in range. It is known that this pull-in range is wide when the magnification of the objective lens is low and narrow when the magnification of the objective lens is high.

[0006] Therefore, when using an objective lens with a high magnification, the range in which the objective lens can be moved between the front and rear pins to find the position where the objective lens is in focus becomes smaller, making it difficult to detect the position where the objective lens is in focus. [Means for solving the problem]

[0007] The optical device according to the present disclosure comprises a light source that emits illumination light, an objective lens that focuses the illumination light on a sample, a first detection means that is provided at a front-focus position relative to the sample and detects secondary light rays generated when the sample is irradiated with the illumination light, a second detection means that is provided at a back-focus position relative to the sample and detects the secondary light rays, a third detection means that detects the secondary light rays incident through the objective lens, a separation means that separates the secondary light rays into the first and second detection means and the third detection means, a focus control means that controls the focusing of the objective lens on the sample based on the detection results of the first and second detection means, and an optical distance adjustment means that is provided between the separation means and the first and second detection means and is capable of adjusting the optical distance between the separation means and the first and second detection means to a value corresponding to the magnification of the objective lens.

[0008] The control method for an optical device according to the present disclosure includes an optical device having a light source that emits illumination light, an objective lens that focuses the illumination light on a sample, a first detection means that is provided at a front-focus position with respect to the sample and that detects secondary light rays generated when the sample is irradiated with the illumination light, a second detection means that is provided at a back-focus position with respect to the sample and that detects the secondary light rays, a third detection means that detects the secondary light rays that enter through the objective lens, and a separation means that separates the secondary light rays into the first and second detection means and the third detection means, and controls an optical distance adjustment means that is provided between the separation means and the first and second detection means to adjust the optical distance between the separation means and the first and second detection means to a value corresponding to the magnification of the objective lens. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to efficiently focus an objective lens regardless of the magnification of the objective lens. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram schematically illustrating a configuration of an optical device according to a first embodiment. [Figure 2] 10 is a diagram schematically illustrating the relationship between the position of the objective lens and the intensity of reflected light detected by a photodetector. FIG. [Figure 3] FIG. 2 is a diagram schematically illustrating the path of light in an optical device when the magnification of an objective lens is high. [Figure 4] FIG. 2 is a diagram schematically illustrating the path of light in an optical device when the magnification of an objective lens is low. [Figure 5] FIG. 10 is a diagram schematically illustrating a configuration of an optical device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, a specific configuration of this embodiment will be described with reference to the drawings. The following description shows a preferred embodiment of the present disclosure, and the scope of the present disclosure is not limited to the following embodiment. In the following description, parts with the same reference numerals indicate substantially the same content.

[0012] Embodiment 1 An optical device according to a first embodiment will be described. The optical device according to this embodiment is configured to have an optical system for capturing an image of a sample, which is an object. FIG. 1 is a diagram schematically showing the configuration of the optical device according to the first embodiment. The optical device 100 has a light source 1, beam splitters 2 to 4, an objective lens 5, a lens 6, an adjustment lens 7, photodetectors 8 to 10, a focus control unit 11, and a lens control unit 12.

[0013] The light source 1 is configured as a point light source and emits illumination light L1. The light source 1 may be provided with, for example, a laser element and a slit provided in the path of laser light emitted from the laser element, and light that passes through the slit may be emitted as illumination light L1. In FIG. 1 and the following figures showing the configuration of the optical device, the path of light in the optical device is indicated by arrows.

[0014] Illumination light L1 passes through a beam splitter 2, an adjustment lens 7, a beam splitter 3, and an objective lens 5, and is then irradiated onto a sample 90. Reflected light L2 generated by irradiating the sample 90 with illumination light L1 passes through the objective lens 5 and is incident on the beam splitter 3.

[0015] Hereinafter, the reflected light L2 from the sample 90 will also be referred to as a secondary light ray generated when the sample 90 is illuminated with the illumination light L1. However, the secondary light ray is not limited to reflected light. The secondary light ray may be any of various light rays, such as reflected light, transmitted light, scattered light, and fluorescent light, generated when the sample 90 is illuminated with the illumination light L1.

[0016] The objective lens 5 is configured to be drivable by a focus control unit 11 along the irradiation direction of illumination light L1 onto the sample 90 so that the focal point FP1 is aligned with the sample 90. Hereinafter, the irradiation direction of illumination light L1 will also be referred to as the Z direction. The focal length of the objective lens 5 is defined as f1.

[0017] The beam splitter 3 splits the incident reflected light L2 toward a lens 6 and an adjustment lens 7 of the detection optical system.

[0018] The reflected light L2 incident on the lens 6 is focused by the lens 6 and then incident on the photodetector 8. Here, the focal length of the lens 6 is assumed to be f3. The photodetector 8 is configured, for example, as a sensor in which light-receiving elements are arranged two-dimensionally, such as a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) sensor, and is configured to acquire a profile of the reflected light L2 required for inspecting the sample 90 and an image of the sample 90. The photodetector 8 is provided at a position conjugate with the position at which the illumination light L1 is focused on the sample 90 by the objective lens 5. The photodetector 8 is also referred to as a third detection unit or third detection means.

[0019] In this configuration, in order to improve the quality of the image of the sample 90 acquired by the photodetector 8, the optical system that irradiates the sample 90 with illumination light L1 from the light source 1 and guides the reflected light L2 from the sample 90 to the photodetector 8 may be configured as a confocal optical system.

[0020] A portion of the reflected light L2 incident on the adjustment lens 7 is reflected by the beam splitter 2 and enters the beam splitter 4. The beam splitter 4 splits the incident reflected light L2 so that it is directed toward the photodetectors 9 and 10, respectively.

[0021] In this configuration, the focal point FP2 of the adjustment lens 7 coincides with the emission point of the illumination light L1 from the light source 1. Here, the focal length of the adjustment lens 7 is set to f2. Therefore, the focal point FP2 of the reflected light L2 separated by the beam splitter 4 is located at a position conjugate with the emission point of the illumination light L1 from the light source 1. Note that, hereinafter, the focal length f2 of the adjustment lens 7 will also be referred to as the first focal length.

[0022] The photodetectors 9 and 10 and the focus control unit 11 constitute a front-focus / rear-focus focusing control mechanism that drives the objective lens 5 in the Z direction so that the focal point FP1 of the objective lens 5 is aligned with the sample 90. The photodetectors 9 and 10 are configured as light-receiving elements such as photodiodes, and are configured to be able to detect the intensity of the incident reflected light L2. The photodetector 9 is also referred to as a second detection unit or second detection means, and the photodetector 10 is also referred to as a first detection unit or first detection means.

[0023] The photodetectors 9 and 10 are arranged at different optical distances from the beam splitter 4. In this example, the optical distance between the photodetector 9 and the beam splitter 4 is longer than the optical distance between the photodetector 10 and the beam splitter 4. Therefore, the photodetector 9 is arranged at a position farther away from the focal point FP2 of the reflected light L2 (back focus position), and the photodetector 10 is arranged at a position closer to the focal point FP2 of the reflected light L2 (front focus position).

[0024] The photodetectors 9 and 10 output to the focus control unit 11 detection signals DET1 and DET2, respectively, which indicate the intensity of the received reflected light L2.

[0025] The focus control unit 11 is configured as a drive mechanism that can adjust the position of the objective lens 5 in the Z direction based on the detection signals DET1 and DET2 so that the focal point FP1 of the objective lens 5 is aligned with the sample 90. This allows the focus control unit 11 to drive the objective lens 5 to a position where the focal point FP1 is aligned with the sample 90. The focus control unit 11 can use various drive mechanisms that have drive components such as a motor.

[0026] The adjustment lens 7 and the lens control unit 12 are configured as an optical distance adjusting means capable of adjusting the optical distance between the objective lens 5 and the photodetectors 9 and 10 in response to a control signal CON2 indicating the magnification of the objective lens 5.

[0027] The adjustment lens 7 is configured as a variable-focus lens that can adjust the focal length f2 on the output side of the reflected light L2, i.e., on the side of the beam splitter 2. The adjustment lens 7 may be configured as a zoom lens that combines multiple lenses. Alternatively, the adjustment lens 7 may be configured as a single lens with a variable focal length.

[0028] The lens control unit 12 receives a control signal CON2 indicating the magnification of the objective lens 5, and controls the focal length f2 of the adjustment lens 7 according to the magnification of the objective lens 5 using the control signal CON1.

[0029] Furthermore, the adjustment lens 7 is not limited to a single lens. For example, the lens control unit 12 may be configured to select a lens corresponding to the objective lens 5 from a plurality of lenses with different focal lengths as the adjustment lens 7, and to place the selected lens between the beam splitter 3 and the photodetectors 9 and 10.

[0030] Next, focusing control using the front focus / rear focus method will be described. As described above, the optical device 100 is configured so that the focal point FP2 of the reflected light L2 is rear-focused with respect to the photodetector 9 and front-focused with respect to the photodetector 10. In focusing control using the front focus / rear focus method, the amount of light detected by the photodetectors 9 and 10 changes as the position of the objective lens 5 in the Z direction relative to the sample 90 changes.

[0031] 2 is a diagram schematically showing the relationship between the position of the objective lens 5 in the Z direction and the intensity of the reflected light detected by the photodetectors 9 and 10. Since the positions of the focal point FP2 of the reflected light L2 relative to the photodetectors 9 and 10 are different, as shown in FIG. 2, when the position of the objective lens 5 in the Z direction is taken as the horizontal axis, the peak of the detection signal DET1 indicating the intensity of the reflected light L2 detected by the photodetector 9 and the peak of the detection signal DET2 indicating the intensity of the reflected light L2 detected by the photodetector 10 are located at positions apart from each other. In front-focus / rear-focus focusing control, the distance between the peak of the detection signal DET1 and the peak of the detection signal DET2 is generally referred to as the pull-in range D.

[0032] When the photodetectors 9 and 10 are placed in appropriate positions, the position where the intensity of the detection signal DET1 and the intensity of the detection signal DET2 are balanced is the position where the focal point FP1 of the objective lens 5 is aligned with the sample 90. Therefore, by the focus control unit 11 monitoring the detection signals DET1 and DET2, it is possible to drive the objective lens 5 to the position where the focal point FP1 is aligned with the sample 90.

[0033] At this time, the focus control unit 11 may detect the position where the error signal E based on the difference between the detection signals DET1 and DET2 becomes 0 as the position where the focal point FP1 of the objective lens 5 is aligned with the sample 90 (sometimes referred to as the just-focus position). The error signal E may be defined by, for example, the following equation. E = (DET1 - DET2) / (DET1 + DET2)

[0034] Next, we will explain the effect of the magnification of the objective lens 5 on the front-focus / rear-focus focusing control. A typical optical system does not have a configuration in which an adjustment lens 7 is provided to change the focal length, as in the optical device 100. Therefore, when the magnification of the objective lens 5 is changed, the above-mentioned pull-in range D changes. When the magnification of the objective lens 5 is high (for example, 100x), the pull-in range D becomes narrower than when the magnification of the objective lens 5 is low (for example, 10x). This will be explained in detail below.

[0035] The pull-in range D is determined by the optical distance L between the focal point FP2 of the reflected light L2 incident on the photodetectors 9 and 10 and the photodetectors 9 and 10, the focal length f1 of the objective lens 5, and the focal length f2 of the adjustment lens 7 on the light source 1 side. Note that, hereinafter, the focal length f1 of the objective lens 5 is also referred to as the second focal length.

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[0036] In a typical optical system, a fixed-focus relay lens or the like is placed at the position of the adjustment lens 7. That is, when the magnification of the objective lens 5 is changed while the focal length f2 is fixed, only the focal length f1 of the objective lens 5 is changed. Therefore, the value of α changes, and the pull-in range D fluctuates.

[0037] When the magnification of the objective lens 5 is low, that is, when the focal length f1 is long, α becomes small. As a result, the pull-in range D becomes large. On the other hand, when the magnification of the objective lens 5 is high, that is, when the focal length f1 is short, α becomes large. As a result, the pull-in range D becomes small. In other words, in a front-focus / rear-focus focus detection mechanism used in a typical optical device, the pull-in range D between front focus and rear focus becomes narrower as the magnification of the objective lens 5 becomes higher.

[0038] Therefore, since the range in which the objective lens 5 can be moved in the Z direction between the front pin and the rear pin while ensuring the effectiveness of the front pin / rear pin focusing control is narrowed, high accuracy is required for positioning the objective lens 5 to the just focus position. As a result, when the magnification of the objective lens 5 is high, problems may arise such as time required for focusing control and deterioration of focusing accuracy.

[0039] In order to eliminate the difficulty in controlling focus due to the magnification of the objective lens 5 described above, the optical device 100 of this embodiment is configured to prevent or suppress fluctuations in the pull-in range D due to changes in the magnification of the objective lens 5 by suitably controlling the focal length f2 of the adjustment lens 7.

[0040] The following describes the control of the focal length f2 of the adjustment lens 7 of the optical device 100. The lens control unit 12 uses the control signal CON1 to instruct the adjustment lens 7 on the focal length f2 that will make the value of α a desired value when the magnification of the objective lens 5 indicated by the control signal CON2 is applied. This allows the focal length f2 of the adjustment lens 7 to be the desired focal length that corresponds to the magnification of the objective lens 5 indicated by the control signal CON2.

[0041] FIG. 3 is a diagram showing a schematic view of the path of light in an optical device when the magnification of the objective lens is high. FIG. 4 is a diagram showing a schematic view of the path of light in an optical device when the magnification of the objective lens is low. In FIG. 3, the focal length of the high-magnification objective lens 5 is set to f1. A , adjust the focal length of lens 7 to f2 A In FIG. 4, the focal length of the low-magnification objective lens 5 is set to f1 B , adjust the focal length of lens 7 to f2 B The focal length of the adjustment lens 7 is f2 A and the focal length of the adjustment lens 7 is f2 B , all of which coincide with the emission point of the illumination light L1 from the light source 1.

[0042] 3 and 4, for the sake of convenience, the position of the adjustment lens 7 is different, but this does not necessarily mean that the position of the adjustment lens 7 is actually different. If the adjustment lens 7 is configured as a variable focus lens such as a zoom lens that can change the focus without changing the position or shape, it goes without saying that the position of the adjustment lens 7 does not have to change even if the magnification of the objective lens 5 is changed.

[0043] When the magnification of the objective lens 5 is high, the lens control unit 12 controls the adjustment lens 7 so that the focal length f2 becomes shorter, as shown in Fig. 3. When the magnification of the objective lens 5 is low, the lens control unit 12 controls the adjustment lens 7 so that the focal length f2 becomes longer, as shown in Fig. 4.

[0044] At this time, it is desirable that the lens control unit 12 instructs the focal length f2 to the adjustment lens 7 so that α can be kept constant regardless of the magnification of the objective lens 5, that is, so that the ratio between the focal length f1 of the objective lens and the focal length f2 of the adjustment lens 7 can be kept constant. This makes it possible to maintain the pull-in range D constant.

[0045] Furthermore, even if α cannot be maintained at a constant setting value depending on the magnification of the objective lens 5, it is desirable for the lens control unit 12 to instruct the focal length f2 to the adjustment lens 7 so that it is a value within a predetermined range that is as close as possible to the setting value, that is, so that the ratio between the focal length f1 of the objective lens and the focal length f2 of the adjustment lens 7 is a value within a predetermined range. This allows the pull-in range D to be set to a value greater than the predetermined value.

[0046] The photodetector 8 used to image the sample 90 receives the reflected light L2 from the sample 90 without passing through the adjustment lens 7. Therefore, an image of the sample 90 can be acquired regardless of changes in the magnification of the objective lens 5.

[0047] Therefore, with this configuration, even when the magnification of the objective lens is changed, the focal length of the adjustment lens 7 can be suitably changed to maintain the pull-in range D constant or within a desired range. This allows the focus FP1 of the objective lens 5 to be efficiently adjusted to the sample 90 regardless of the magnification of the objective lens 5.

[0048] Embodiment 2 An optical device according to a second embodiment will be described below. The optical device according to the second embodiment is configured to further include a mechanism for changing the magnification of the objective lens.

[0049] 5 is a diagram schematically illustrating the configuration of an optical device 200 according to the second embodiment. Compared to the optical device 100 according to the first embodiment, the optical device 200 further includes a magnification changing unit 13. The magnification changing unit 13 switches the magnification of the objective lens 5 in response to a control signal CON2 that indicates the magnification of the objective lens 5 and is given by a user or the like.

[0050] When the magnification can be changed using the same lens, such as when the objective lens 5 is configured as a variable magnification lens, the magnification change unit 13 may switch the magnification of the objective lens 5 by providing a control signal CON3 to the objective lens 5, as shown in Figure 5.

[0051] The magnification change unit 13 may also be configured to select an objective lens from a plurality of objective lenses with different magnifications in response to the control signal CON2 and use it as the objective lens 5. For example, the magnification change unit 13 may have a mechanism that selects an objective lens to be used as the objective lens 5 from a plurality of objective lenses attached to a revolver by driving the revolver.

[0052] As described above, according to this configuration, the focal length of the adjustment lens 7 is suitably changed while the magnification of the objective lens 5 is automatically changed in response to the control signal CON2, thereby maintaining the pull-in range D constant or within a desired range. As a result, similar to the first embodiment, the focal point FP1 of the objective lens 5 can be efficiently adjusted to the sample 90 regardless of the magnification of the objective lens 5.

[0053] Other embodiments Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above-described embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate.

[0054] The configuration of the optical device described above is merely an example, and other configurations may be used as long as the illumination light L1 emitted from the light source 1 can be irradiated onto the sample 90 and secondary light rays from the sample 90 can be detected by the photodetectors 8 to 10. For example, although the optical device according to the above embodiment has been described as having a refractive optical system, the optical device may be configured to have a refractive reflective optical system or a reflective optical system, and to have means for adjusting the focal length of the secondary light rays in the same manner as the adjusting lens 7, as needed.

[0055] Furthermore, the focus control unit 11 has been described as driving the objective lens 5 to a position where the focal point FP1 is aligned with the sample 90, but this is not limiting. The focus control unit 11 may be any unit that changes the relative position between the sample 90 and the objective lens 5, and may also be a unit that drives a stage that holds the sample 90, etc.

[0056] Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above-described embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate.

[0057] Each drawing is merely an example for describing one or more embodiments. Each drawing may relate not only to one particular embodiment, but also to one or more other embodiments. As will be understood by those skilled in the art, various features or steps described with reference to any one drawing can be combined with features or steps shown in one or more other drawings to create, for example, an embodiment not explicitly shown or described. Not all features or steps shown in any one drawing are necessary to describe an exemplary embodiment, and some features or steps may be omitted. The order of steps described in any drawing may be changed as appropriate. [Explanation of symbols]

[0058] 1 light source 2~4 Beam splitter 5 Objective Lenses 6 Lenses 7 Adjustment Lens 8~10 photodetectors 11 Focus control section 12 Lens control unit 13 Magnification change section 90 samples 100, 200 optical equipment CON1~CON3 control signals DET1, DET2 detection signal L1 illumination light L2 reflected light

Claims

1. a light source that emits illumination light; an objective lens that focuses the illumination light onto a sample; a first detection means provided at a front-focus position relative to the sample, for detecting a secondary light ray generated when the sample is irradiated with the illumination light; a second detecting means provided at a back-focus position with respect to the sample and detecting the secondary beam; a third detecting means for detecting the secondary light beam incident through the objective lens; a splitting means for splitting the secondary light beam to the first and second detecting means and the third detecting means; a focus control means for controlling the focusing of the objective lens on the sample based on the detection results of the first and second detection means; an optical distance adjusting means provided between the separating means and the first and second detecting means, and capable of adjusting the optical distance between the separating means and the first and second detecting means to a value corresponding to the magnification of the objective lens; optical equipment.

2. the optical distance adjusting means has a variable focus lens capable of adjusting a first focal length on the side of the first and second detecting means, and controls the first focal length of the variable focus lens to a value corresponding to the magnification of the objective lens; The optical device according to claim 1 .

3. The variable focus lens is configured as a zoom lens made up of a combination of multiple lenses.

3. The optical device according to claim 2.

4. the optical distance adjusting means controls the first focal length so that a pull-in range between the front focus and the rear focus due to a change in the magnification of the objective lens becomes larger than a predetermined value, or so that the pull-in range is constant regardless of a change in the magnification of the objective lens.

4. The optical device according to claim 2 or 3.

5. the optical distance adjusting means controls the first focal length so that a ratio between the first focal length and the second focal length of the objective lens is within a predetermined range or so that the ratio is constant regardless of a change in the magnification of the objective lens.

5. The optical device according to claim 4.

6. the optical distance adjusting means has a plurality of lenses with different focal lengths, and a lens having a focal length corresponding to the magnification of the objective lens selected from the plurality of lenses is disposed between the separating means and the first and second detecting means; The optical device according to claim 1 .

7. an optical system including at least the light source and the third detecting means constitutes a confocal optical system; 7. An optical device according to any one of claims 1 to 3 and 6.

8. the third detection means is provided at a position conjugate with a position at which the illumination light is focused on the sample by the objective lens; 7. An optical device according to any one of claims 1 to 3 and 6.

9. further comprising a magnification changing means for changing the magnification of the objective lens in accordance with information specifying the magnification of the objective lens; the optical distance adjusting means controls the optical distance between the separating means and the first and second detecting means so that the optical distance becomes a value corresponding to the magnification of the objective lens designated by the information.

7. An optical device according to any one of claims 1 to 3 and 6.

10. an objective lens for focusing the illumination light on a sample; a first detecting means provided at a front-focus position relative to the sample and detecting a secondary light ray generated when the sample is irradiated with the illumination light; a second detecting means provided at a back-focus position relative to the sample and detecting the secondary light ray; a third detecting means for detecting the secondary light ray incident via the objective lens; and a separating means for separating the secondary light ray into the first and second detecting means and the third detecting means; performing focusing control of the objective lens relative to the sample based on the detection results of the first and second detection means; an optical distance adjusting means provided between the separating means and the first and second detecting means is controlled to adjust the optical distance between the separating means and the first and second detecting means to a value corresponding to the magnification of the objective lens; A method for controlling an optical device.

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