Optical microscopy with flexible axial capabilities using a vari‐focus liquid lens

Abstract

The axial imaging range of optical microscopy is restricted by its fixed working plane and limited depth of field. In this paper, the axial capabilities of an off-the-shelf microscope is improved by inserting a liquid lens, which can be controlled by a driving electrical voltage, into the optical path of the microscope. First, the numerical formulas of the working distance and the magnification with the variation of the focus of the liquid lens are inferred using a ray tracing method and conclusion is obtained that the best position for inserting a liquid lens with consistent magnification is the aperture plane and the rear focal plane of the objective lens. Second, with the liquid lens embedded in the microscope, the numerical relationship between the magnification and the working distance of the proposed flexible-axial-capability microscope and the liquid lens driving voltage is calibrated and fitted using the inferred numerical formulas. Third, techniques including autofocus, extending depth of field and three-dimensional imaging are researched and applied, improving the designed microscope to not only flexibly control its working distance, but also to extend the depth of field near the variable working plane. Experiments show that the presented flexible-axial-capability microscope has a long working distance range of 8 mm, and by calibrating the magnification curve within the working distance range, samples can be observed and measured precisely. The depth of field can be extended to 400 μm from the variable working plane and is 20 times that of the off-the-shelf microscope.

Nonmechanical and multiview 3D measurement microscope for workpiece with large slope and complex geometry

“…There is a linear dependence between the shift of the image plane and the driving current (Fahrbach et al ., ; Qu & Yang, ). The calibration curve for the 5× lens is presented in Figure , and the line fit result is where z represents the focal plane offset and I represents the driving current.…”

“…When the liquid lens scans in the axial direction, neither the microscope objective nor the observed workpiece moves mechanically, but the imaging plane of the microscopic system is axially displaced, which indicates that the working distance of the system has changed. There is a linear dependence between the shift of the image plane and the driving current (Fahrbach et al, 2013;Qu & Yang, 2015). The calibration curve for the 5× lens is presented in Figure 5, and the line fit result is…”

A self-adaptive and nonmechanical motion autofocusing system for optical microscopes

“…The proposed self-adaptive nonmechanical motion AF system consists of a microscope (Pomeas 3D Video Microscope, Dongguan, China), a CCD detector (Basler a102fc, Ahrensburg, Germany), an image receiver with an IEEE-1394 interface, a liquid lens (Optotune EL-10-30-Ci, Dietikon, Switzerland) and an associated controller (Optotune, Dietikon, Switzerland), and a host computer (3.10 GHz 3 2 CPU, 4.0 GB RAM). According to previous work (Qu & Yang, 2015), the magnification of the optical microscope does not change when the liquid lens was attached to the CCD plane or the rear focal plane of the objective.…”

Analysis of axial scanning range and magnification variation in wide‐field microscope for measurement using an electrically tunable lens

“…Electrically tunable lenses (ETLs), such as liquid lenses and tunable acoustic gradient (TAG) lenses, have the advantages of nonmechanical axial scanning, fast response, low power consumption, easy control, compact size, and wide focal length variation range. Inserting an ETL into different optical systems can enable fast zooming (Li, Cheng, & Hao, ), extended depth of field (Liu & Hua, ; Zhao & Qu, ), fast axial scanning (Grewe, Voigt, & van‘t Hoff, & Helmchen, ; Jabbour et al, ; Martínez‐Corral et al, ), auto focusing (Qu & Yang, ), and three‐dimensional imaging (Duocastella, Sun, & Arnold, ; Fahrbach, Voigt, Schmid, Helmchen, & Huisken, ). However, when an ETL lens is introduced into a microscope, the image quality of the microscope, determined by resolution, contrast, and magnification, is usually modified.…”