A method for correcting the parallelism of the optical axis of infrared and low-light image intensifier objective lenses

Abstract

This invention relates to the field of optical axis correction technology and discloses a method for correcting the parallelism of the optical axes of infrared and low-light image intensifier objectives, comprising the following steps: S1, correcting the parallelism of the optical axes of a high-precision field of view instrument and an autocollimating front mirror; S2, preparing a high-precision product adapter bracket and a reflector, and adjusting the position of the high-precision product adapter bracket; S3, correcting the field of view of the low-light image intensifier objective; S4, correcting the position of the projection reticle of the low-light image intensifier; S5, correcting the parallelism of the optical axes of the low-light image intensifier objective and the infrared objective. This method can accurately correct the parallelism of the optical axes of the infrared objective and the low-light image intensifier objective, thus providing an important foundation and support for achieving back-end fusion imaging registration.

Description

Technical Field

[0001] This invention relates to the field of optical axis correction technology, and in particular to a method for correcting the parallelism of the optical axes of infrared and low-light image intensifier objectives, used to achieve parallelism adjustment of the optical axes of uncooled infrared objectives and low-light image intensifier objectives. Background Technology

[0002] With the continuous maturation and breakthroughs in uncooled infrared thermal imaging technology, as well as the mass production and application of second-generation and third-generation low-light image intensifiers, new observation mirrors and telescopes that use uncooled infrared thermal imagers and low-light image intensifiers for optoelectronic fusion have become a hot research area in recent years.

[0003] Uncooled infrared thermal imagers can output video signals to a miniature OLED display via digital signal transmission. However, currently available low-light image intensifiers cannot directly output digital images; they can only achieve imaging through a back-end optical system. Therefore, when infrared and low-light images need to be fused, the infrared image displayed on the miniature OLED must be projected onto the low-light optical imaging channel for fusion registration. Before this process, the optical axis parallelism of the infrared objective and the low-light image intensifier objective must be corrected.

[0004] Because infrared images are digital, electronic reticles (which can be blanked) can be overlaid and displayed, enabling precise positioning of the field of view center. However, low-light image intensifiers cannot output digital images. In devices such as observation mirrors, it is often required that the image be displayed without reticles. Traditional optical reticles cannot be used in the system. This results in the image output by the low-light image intensifier lacking an intermediate reference, and the parallelism between its optical axis and the optical axes of other optical paths cannot be guaranteed during the optical axis correction process.

[0005] Therefore, based on the above technical issues, improvements are needed. Summary of the Invention

[0006] To address the technical problems existing in the prior art, the present invention provides a method for correcting the parallelism of the optical axis of infrared and low-light image intensifier objective lenses.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for correcting the parallelism of the optical axis of an infrared and low-light image intensifier objective lens, comprising the following steps:

[0008] S1. Correct the parallelism of the optical axes of the high-precision field of view and the autocollimating front mirror so that the crosshairs of the autocollimating front mirror and the crosshairs in the field of view of the high-precision field of view coincide.

[0009] S2. Prepare a high-precision product adapter bracket and a reflector. The high-precision product adapter bracket is provided with a reference surface one connected to the low-light image intensifier and a reference surface two for placing the reflector. Adjust the position of the high-precision product adapter bracket so that the reference surface two represents the optical axis of the low-light image intensifier.

[0010] S3. Install the low-light image intensifier on the reference plane one, and correct the field of view of the objective lens of the low-light image intensifier so that the absolute values ​​of the scale values ​​of the field meter on the imaging plane of the low-light image intensifier are equal in the vertical and horizontal directions.

[0011] S4. Prepare the reticle projection fixture to visualize the center of the optical axis of the low-light image intensifier objective lens, and correct the position of the low-light image intensifier projection reticle so that the low-light image intensifier projection reticle coincides with the center reticle position of the high-precision field instrument.

[0012] S5. Correct the parallelism of the optical axes of the low-light image intensifier objective and the infrared objective.

[0013] Preferably, step S1 specifically includes:

[0014] Prepare an optical platform one. Place the high-precision field instrument and the autocollimating front mirror opposite each other on the optical platform one. Adjust the positions of the high-precision field instrument and the autocollimating front mirror. Observe through the eyepiece end of the autocollimating front mirror until the crosshairs of the autocollimating front mirror and the crosshairs in the field of view of the high-precision field instrument coincide.

[0015] Preferably, step S2 is as follows:

[0016] Place the high-precision product adapter bracket between the high-precision field of view and the autocollimating front mirror. Place the reflector on the reference plane two of the high-precision product adapter bracket. Observe through the eyepiece end of the autocollimating front mirror and adjust the position of the high-precision product adapter bracket until the crosshairs of the autocollimating front mirror and the reflector crosshairs coincide. Fix the high-precision product adapter bracket.

[0017] Preferably, step S3 is as follows:

[0018] Remove the autocollimating front lens and place the microscope in that position. Observe through the microscope and read the field of view scale value on the imaging surface of the low-light image intensifier. Fine-tune the installation position between the low-light image intensifier and its objective lens until the absolute values ​​of the vertical and horizontal scale values ​​of the field of view on the imaging surface of the low-light image intensifier observed under the microscope are equal. Then fix the low-light image intensifier.

[0019] Preferably, step S4 is as follows:

[0020] Prepare a reticle projection fixture, which includes a rectangular frame and a reticle generation device connected within the rectangular frame. The reticle generation device includes a docking prism, a projection lens, a reticle plate, and an illumination lamp. Fix the reticle projection fixture on the objective lens of the low-light image intensifier. Observe the projected reticle on the imaging surface of the low-light image intensifier through a microscope. Adjust the position of the reticle projection fixture until the projected reticle observed in the microscope coincides with the center reticle position of the high-precision field instrument.

[0021] Preferably, the rectangular frame is provided with a plurality of internally threaded holes, and a fixed top rod is internally threaded into each of the threaded holes, and an adjusting handwheel is connected to the fixed top rod.

[0022] Preferably, step S5 is as follows:

[0023] Prepare an optical platform two. On this platform, place the reflective collimator, crosshair thermal target, infrared video display fixture, and high-precision six-degree-of-freedom adjustment platform in sequence. The center of the high-precision six-degree-of-freedom adjustment platform should be aligned with the center of the crosshair thermal target and the center of the reflective collimator. Install the low-light image intensifier and its objective lens, calibrated in step S4, and the high-precision product adapter on the high-precision six-degree-of-freedom adjustment platform. Place the microscope in front of the imaging plane of the low-light image intensifier. Install the uncooled infrared core in the uncooled infrared core mounting position of the low-light image intensifier objective lens assembly. Connect the microscope to the uncooled infrared core using the infrared video display fixture. The cooled infrared camera mechanism is connected and displays an infrared image. The high-precision six-degree-of-freedom adjustment platform is adjusted. The image on the imaging surface of the low-light image intensifier is observed through a microscope to locate the position of the crosshair thermal target. The projection reticle on the imaging surface of the low-light image intensifier observed under the microscope is aligned with the center of the crosshair thermal target. The high-precision six-degree-of-freedom adjustment platform is then fixed. The infrared video image on the infrared video display fixture is observed, and the installation position of the uncooled infrared camera mechanism is finely adjusted until the position of the electric crosshair in the infrared video image coincides with the position of the crosshair thermal target. The uncooled infrared camera mechanism is then tightened, thus completing the parallelism correction of the optical axes of the infrared and low-light image intensifier objectives.

[0024] This invention was tested and verified using a reflective collimator, a cross-shaped thermal target, an optical platform, a high-precision six-degree-of-freedom adjustment platform, a high-precision field of view, a high-precision product adapter bracket, a reticle projection fixture, and a fusion-type observation mirror prototype. This method can accurately correct the parallelism of the optical axes of the infrared objective and the low-light image intensifier, thus providing an important foundation and support for achieving back-end fusion imaging registration. Attached Figure Description

[0025] Figure 1 This is a flowchart of the overall workflow of this embodiment.

[0026] Figure 2 This is a schematic diagram showing the placement of the high-precision field of view and the autocollimating front mirror in step S1 of this embodiment.

[0027] Figure 3 This is a schematic diagram of the placement of the high-precision product adapter bracket in step S2 of this embodiment.

[0028] Figure 4 This is a schematic diagram of the optical axis of the high-precision field of view and the autocollimating front mirror in step S2 of this embodiment.

[0029] Figure 5 This is a schematic diagram showing the placement of the low-light image intensifier assembly with objective lens in step S3 of this embodiment.

[0030] Figure 6 This is a schematic diagram of the optical axis of the low-light image intensifier objective lens after correction in step S3 of this embodiment.

[0031] Figure 7 This is a schematic diagram of the reticle projection fixture in step S4 of this embodiment.

[0032] Figure 8 This is a schematic diagram of the installation of the reticle projection fixture in step S4 of this embodiment.

[0033] Figure 9 This is a schematic diagram showing the placement of the low-light image intensifier objective and the infrared objective in step S5 of this embodiment.

[0034] In the diagram: 1. Optical Platform 1; 2. High-precision field instrument; 3. Autocollimating front mirror; 4. High-precision product adapter bracket; 5. Reflector; 6. Reference plane 1; 7. Reference plane 2; 8. Low-light image intensifier; 9. Reticle projection fixture; 10. Rectangular frame; 11. Reticle generation device; 12. Microscope; 13. Fixed top rod; 14. Optical Platform 2; 15. Reflective collimator; 16. Cross-shaped thermal target; 17. Infrared video display fixture; 18. High-precision six-DOF adjustment platform. Detailed Implementation

[0035] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Example

[0037] This embodiment uses a fusion-type observation mirror as an example for illustration, but the method is not limited to this type of product. The fusion-type observation mirror has dual-channel objectives: an infrared objective and a low-light image intensifier objective. In the initial stage of product assembly, the parallelism of the dual-channel objectives needs to be corrected to facilitate pixel-level fusion of the infrared output digital image and the low-light image intensifier optical image. The method of this embodiment can complete the parallelism correction of the dual-channel objectives. Before performing the calibration, the following instruments and fixtures need to be prepared: a reflective collimator, a crosshair thermal target, an optical platform, a high-precision six-degree-of-freedom adjustment platform, a high-precision field instrument, an autocollimating front mirror, a reflecting mirror, a high-precision product adapter bracket, a reticle projection fixture, an infrared video display fixture, a low-light image intensifier assembly with objectives, and a microscope.

[0038] The overall workflow of this embodiment is as follows: Figure 1 As shown below, the calibration method will be explained in detail in conjunction with the overall workflow.

[0039] A method for correcting the parallelism of the optical axis of an infrared and low-light image intensifier objective lens, characterized by comprising the following steps:

[0040] S1. Correct the parallelism of the optical axes of the high-precision field instrument and the autocollimating front mirror, so that the crosshairs of the autocollimating front mirror coincide with the crosshairs within the field of view of the high-precision field instrument. Specifically,

[0041] Prepare an optical platform 1, and place the high-precision field of view 2 and the autocollimating front mirror 3 opposite each other on the optical platform 1 (the positional relationship is as follows). Figure 2 As shown), adjust the positions of the high-precision field instrument and the autocollimating front mirror, and observe through the eyepiece end of the autocollimating front mirror until the crosshairs (optical axis one) of the autocollimating front mirror and the crosshairs (optical axis two) in the field of view of the high-precision field instrument coincide.

[0042] S2. Prepare a high-precision product adapter bracket 4 and a reflector 5. The high-precision product adapter bracket has a reference surface 6 for connecting to the low-light image intensifier and a reference surface 7 for placing the reflector. Adjust the position of the high-precision product adapter bracket so that the reference surface 7 represents the optical axis of the low-light image intensifier. Specifically,

[0043] The high-precision product adapter bracket is arranged according to... Figure 3 The position shown is between the high-precision field instrument and the autocollimating front mirror. Place the reflector on the reference surface two of the high-precision product adapter bracket (ensuring a tight fit). Observe through the eyepiece end of the autocollimating front mirror and adjust the position of the high-precision product adapter bracket until the crosshairs of the autocollimating front mirror and the reflector crosshairs coincide. Fix the high-precision product adapter bracket. After the optical axes of the high-precision field instrument and the autocollimating front mirror are corrected, as shown... Figure 4 As shown;

[0044] S3. Mount the low-light image intensifier 8 with the objective lens on the reference plane one (ensuring a tight fit). Correct the field of view of the low-light image intensifier objective lens to ensure that the absolute values ​​of the vertical and horizontal scales on the imaging plane of the low-light image intensifier are equal. Specifically,

[0045] Remove the autocollimating front lens and place the microscope 12 in that position (see Figure 5 By observing under a microscope, the scale values ​​of the field meter on the imaging plane of the low-light image intensifier are read. The installation position between the low-light image intensifier and its objective lens is finely adjusted until the absolute values ​​of the vertical and horizontal scale values ​​of the field meter on the imaging plane of the low-light image intensifier observed under the microscope are equal. The low-light image intensifier is then fixed in place. After the optical axis of the low-light image intensifier objective lens is corrected, as shown... Figure 6 As shown;

[0046] S4. Prepare the reticle projection fixture to visualize the center of the optical axis of the low-light image intensifier objective lens. Correct the position of the projected reticle of the low-light image intensifier so that it coincides with the center reticle position of the high-precision field instrument. Specifically...

[0047] See Figure 7 Prepare a reticulum projection fixture 9, which includes a rectangular frame 10 and a reticulum generation device 11 connected within the rectangular frame. The reticulum generation device includes a docking prism, a projection lens, a reticle, and an illumination lamp. The rectangular frame has several internally threaded holes, and a fixing rod 13 is internally threaded into each of the threaded holes. The fixing rod is connected to an adjusting handwheel.

[0048] See Figure 8 Fix the reticle projection fixture on the objective lens of the low-light image intensifier. Observe the projected reticle on the imaging surface of the low-light image intensifier through a microscope. Adjust the position of the reticle projection fixture until the projected reticle observed in the microscope coincides with the center reticle position of the high-precision field instrument. At this time, the position of the projected reticle represents the center position of the field of view of the objective lens of the low-light image intensifier.

[0049] S5. Correct the parallelism of the optical axes of the low-light image intensifier objective and the infrared objective, specifically as follows:

[0050] Prepare an optical platform 2 14, and place the reflective collimator 15, the cross-shaped thermal target 16, the infrared video display fixture 17, and the high-precision six-degree-of-freedom adjustment platform 18 on the optical platform 2 in sequence (the positional relationship is as follows). Figure 9As shown), the center of the high-precision six-degree-of-freedom adjustment platform, the center of the crosshair thermal target, and the center of the reflective collimator should be aligned (approximate alignment is sufficient; precise alignment is not required). Install the low-light image intensifier and its objective lens, along with the high-precision product adapter bracket, which were calibrated in step S4, onto the high-precision six-degree-of-freedom adjustment platform. Place the microscope 12 at the front end of the low-light image intensifier's imaging surface. Install the uncooled infrared core onto the uncooled infrared core mounting position of the low-light image intensifier objective lens assembly. Connect the infrared video display fixture to the uncooled infrared core and display the infrared image (with crosshairs). Adjust the high-precision six-degree-of-freedom adjustment platform, observe the image on the imaging surface of the low-light image intensifier through a microscope, locate the position of the cross-shaped thermal target, and align the projection reticle on the imaging surface of the low-light image intensifier with the center of the cross-shaped thermal target. Fix the high-precision six-degree-of-freedom adjustment platform; observe the infrared video image on the infrared video display fixture, fine-tune the installation position of the uncooled infrared core until the position of the electric cross in the infrared video image coincides with the position of the cross-shaped thermal target, and tighten the uncooled infrared core. This completes the parallelism correction of the optical axes of the infrared and low-light image intensifier objectives.

[0051] The first reference surface of the high-precision product adapter bracket serves as the reference surface connecting the high-precision product adapter bracket to the low-light image intensifier assembly with objective lens; the second reference surface is used to place the reflector. Both reference surfaces are designed with high-precision geometric tolerances to ensure consistency between the two references. In step S2, the reference surface of the high-precision product adapter bracket is fixedly connected to the reference surface of the low-light image intensifier assembly with objective lens, thereby enabling reference surface two to represent the optical axis of the low-light image intensifier assembly with objective lens. By correcting the autocollimated image of reference surface two and the autocollimating front mirror, the perpendicularity of the optical axis of reference surface two and the autocollimating front mirror is ensured, thus ensuring that the low-light image intensifier assembly with objective lens is parallel to the optical axis of the high-precision field instrument.

[0052] The reticle generation device works as follows: an illumination lamp lights the reticle pattern, which is then collimated by a projection lens and enters the objective lens of a low-light image intensifier via a docking prism. This allows the reticle pattern to be generated on the imaging surface of the low-light image intensifier. The reticle generation device uses an existing commercially available crosshair laser module.

[0053] When the reticle projection fixture is fixed on the objective lens of the low-light image intensifier, a rectangular frame is placed over the outside of the objective lens, and the objective lens is clamped by three fixing rods to fix the reticle projection fixture. The position of the reticle projection fixture can be adjusted by adjusting the handwheel to extend and retract the fixing rods, thereby adjusting the position of the reticle pattern in the display field of view.

[0054] The reticle projection fixture is used to visualize the center of the optical axis of its objective lens. In this embodiment, taking a fusion observation mirror as an example, a reticle projection fixture that can be installed on its low-light image intensifier objective lens is designed.

[0055] After completing steps S1 to S4, the center position of the low-light image intensifier objective is corrected and visualized. This is a necessary prerequisite for achieving parallelism correction of the optical axes of the infrared objective and the low-light image intensifier objective. Since the infrared image is a digital image, the field of view center can be calculated based on the number of imaging pixels during the image setup process, and a corresponding crosshair (which can be hidden) can be generated.

[0056] The cross-shaped thermal target in step S5 is a component on the reflective collimator, and a general-purpose display can be used for the infrared video display fixture.

[0057] This embodiment is a method for aligning the optical axes based on the needs of novel fusion observation mirrors and telescopes, and it forms an important foundation for subsequent dual-path optoelectronic image fusion. After correcting the objective optical axes using this method, not only can the uniform and symmetrical distribution of the field of view of the infrared objective and the low-light image intensifier objective, as well as the optimal image quality of the objective imaging, be guaranteed, but the parallelism requirement of the two objective optical axes can also be achieved. The high parallelism requirement of the infrared objective and the low-light image intensifier objective lays the necessary foundation for pixel-level fusion of the infrared output digital image and the low-light image intensifier optical image at the later stage.

[0058] This method is a means of optical axis parallelism adjustment derived from the requirements of new fusion observation mirrors and telescopes. This method differs from traditional reticle-based dual- or multi-channel image optical axis correction. Similar observation mirrors and related products often require alignment without reticles, and most of these products rely on approximate alignment, which cannot guarantee precision. This is especially true for new high-tech fusion observation mirrors and similar products that require image fusion at the back end, where the parallelism of the objective lens's optical axis is essential. This method allows visualization of the optical axis of the low-light intensifier objective lens, thereby enabling the parallelism correction of the infrared objective lens's optical axis and the low-light image intensifier's optical axis.

[0059] This method has been successfully applied in the actual product assembly and adjustment process. The parallelism index of the infrared objective lens and the objective lens of the low-light image intensifier of the fusion observation lens corrected by this method is less than 30″, thereby achieving a back-end fusion imaging registration accuracy of less than 1 pixel.

[0060] The embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for correcting the parallelism of the optical axis of an infrared and low-light image intensifier objective lens, characterized in that, Includes the following steps: S1. Correct the parallelism of the optical axes of the high-precision field of view and the autocollimating front mirror so that the crosshairs of the autocollimating front mirror and the crosshairs in the field of view of the high-precision field of view coincide. S2. Prepare a high-precision product adapter bracket and a reflector. The high-precision product adapter bracket is provided with a reference surface one connected to the low-light image intensifier and a reference surface two for placing the reflector. Adjust the position of the high-precision product adapter bracket so that the reference surface two represents the optical axis of the low-light image intensifier. S3. Install the low-light image intensifier on the reference plane one, and correct the field of view of the objective lens of the low-light image intensifier so that the absolute values ​​of the scale values ​​of the field meter on the imaging plane of the low-light image intensifier are equal in the vertical and horizontal directions. S4. Prepare the reticle projection fixture to visualize the center of the optical axis of the low-light image intensifier objective lens, and correct the position of the low-light image intensifier projection reticle so that the low-light image intensifier projection reticle coincides with the center reticle position of the high-precision field instrument. S5. Correct the parallelism of the optical axes of the low-light image intensifier objective and the infrared objective; The S5 steps are as follows: Prepare an optical platform two. On this platform, place the reflective collimator, crosshair thermal target, infrared video display fixture, and high-precision six-degree-of-freedom adjustment platform in sequence. The center of the high-precision six-degree-of-freedom adjustment platform should be aligned with the center of the crosshair thermal target and the center of the reflective collimator. Install the low-light image intensifier and its objective lens, calibrated in step S4, and the high-precision product adapter on the high-precision six-degree-of-freedom adjustment platform. Place the microscope in front of the imaging plane of the low-light image intensifier. Install the uncooled infrared core in the uncooled infrared core mounting position of the low-light image intensifier objective lens assembly. Connect the microscope to the uncooled infrared core using the infrared video display fixture. The cooled infrared camera mechanism is connected and displays an infrared image. The high-precision six-degree-of-freedom adjustment platform is adjusted. The image on the imaging surface of the low-light image intensifier is observed through a microscope to locate the position of the crosshair thermal target. The projection reticle on the imaging surface of the low-light image intensifier observed under the microscope is aligned with the center of the crosshair thermal target. The high-precision six-degree-of-freedom adjustment platform is then fixed. The infrared video image on the infrared video display fixture is observed, and the installation position of the uncooled infrared camera mechanism is finely adjusted until the position of the electric crosshair in the infrared video image coincides with the position of the crosshair thermal target. The uncooled infrared camera mechanism is then tightened, thus completing the parallelism correction of the optical axes of the infrared and low-light image intensifier objectives.

2. The method for correcting the parallelism of the optical axis of an infrared and low-light image intensifier objective lens according to claim 1, characterized in that, Step S1 is as follows: Prepare an optical platform one. Place the high-precision field instrument and the autocollimating front mirror opposite each other on the optical platform one. Adjust the positions of the high-precision field instrument and the autocollimating front mirror. Observe through the eyepiece end of the autocollimating front mirror until the crosshairs of the autocollimating front mirror and the crosshairs in the field of view of the high-precision field instrument coincide.

3. The method for correcting the parallelism of the optical axis of an infrared and low-light image intensifier objective lens according to claim 2, characterized in that, The specific steps in S2 are as follows: Place the high-precision product adapter bracket between the high-precision field of view and the autocollimating front mirror. Place the reflector on the reference plane two of the high-precision product adapter bracket. Observe through the eyepiece end of the autocollimating front mirror and adjust the position of the high-precision product adapter bracket until the crosshairs of the autocollimating front mirror and the reflector crosshairs coincide. Fix the high-precision product adapter bracket.

4. The method for correcting the parallelism of the optical axis of an infrared and low-light image intensifier objective lens according to claim 3, characterized in that, The S3 steps are as follows: Remove the autocollimating front lens and place the microscope in that position. Observe through the microscope and read the field of view scale value on the imaging surface of the low-light image intensifier. Fine-tune the installation position between the low-light image intensifier and its objective lens until the absolute values ​​of the vertical and horizontal scale values ​​of the field of view on the imaging surface of the low-light image intensifier observed under the microscope are equal. Then fix the low-light image intensifier.

5. The method for correcting the parallelism of the optical axis of an infrared and low-light image intensifier objective lens according to claim 4, characterized in that, The S4 steps are as follows: Prepare a reticle projection fixture, which includes a rectangular frame and a reticle generation device connected within the rectangular frame. The reticle generation device includes a docking prism, a projection lens, a reticle plate, and an illumination lamp. Fix the reticle projection fixture on the objective lens of the low-light image intensifier. Observe the projected reticle on the imaging surface of the low-light image intensifier through a microscope. Adjust the position of the reticle projection fixture until the projected reticle observed in the microscope coincides with the center reticle position of the high-precision field instrument.

6. The method for correcting the parallelism of the optical axis of an infrared and low-light image intensifier objective lens according to claim 5, characterized in that, The rectangular frame is provided with several internal threaded holes, and a fixed top rod is internally threaded into each threaded hole. An adjusting handwheel is connected to the fixed top rod.

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