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

Abstract

Inserting an electrically tunable lens (ETL), such as liquid lens or tunable acoustic gradient lens, into a microscope can enable fast axial scanning, autofocusing, and extended depth of field.However, placing the ETL at different positions has different influences on image quality. Specially, in a wide-field microscope for measurement, the magnification has to be constant when introducing an ETL, otherwise it will affect measurement accuracy. To determine the best position of ETL, axial scanning range and magnification variation are quantitatively analyzed and discussed in finite and infinite microscopes through theoretical analysis, optical simulation, and experiment for four configurations: when ETL is placed at the back focal plane of objective, at the conjugate plane of objective's back focal plane between two relay lenses, or behind two relay lenses, and at imaging detector plane. The obtained results are as follows. When ETL is placed at the back focal plane, the system has a large scanning range, but the magnification varies because the back focal plane is inside the objective. When ETL is placed between two relay lenses, the magnification stays constant, but the scanning range is small. When ETL is placed behind two relay lenses, the magnification keeps invariant and the scanning range is large, but ETL and two relay lenses are inside the microscope and the system has to be customized.Finally, when ETL is placed at imaging detector plane, the magnification stays constant, but the scanning range is 0, which means the system has no axial scanning capability. Research highlights• An electrically tunable lens (ETL) is introduced into a wide-field microscope for measurement.• Axial scanning range and magnification variation are analyzed and discussed.• Theoretical analysis, ZEMAX optical simulation and experiments are performed. K E Y W O R D S axial scanning range, liquid lens, magnification variation, wide-field microscope for measurement

Electrically tunable lenses – eliminating mechanical axial movements during high-speed 3D live imaging

“…Configuration 3 has not been tested experimentally due to the requirement for a specifically customised setup; however, optical simulation has shown a 0.23% variation in magnification with an axial scanning range of 2.020 mm. Lastly, configuration 4 results in a 14.5% magnification difference across a 31 μm axial scanning range (Qu and Hu, 2019). These results indicate that the ETL should be positioned based on the specific biological investigation; here, the key factors to consider are the desired axial scanning range and whether a constant magnification is required.…”

“…This issue can be solved by positioning the combined ETL and offset lens assembly between two relay lenses at a conjugate of the back focal plane of the detection lens (Fahrbach et al, 2013). The conjugate of the back focal plane corresponds to the position where the image is formed within the optical path (Qu and Hu, 2019) similar to the position of the retina within the human eye. This successfully creates a telecentric configuration (i.e.…”

“…Theoretical analysis and optical simulations of different configurations have further characterised the consequences of ETL positions in a microscopy system (Qu and Hu, 2019): (1) placing the ETL at the back focal plane yields a large scanning range but a varying magnification; (2) positioning the ETL between two relay lenses retains constant magnification but as a consequence decreases the axial scanning range; (3) placing the ETL behind two relay lenses maintains the magnification and produces a large axial scanning range, but constitutes a configuration that can only be achieved through customisation; and lastly (4) positioning the ETL at the imaging detector plane allows a constant magnification without any axial scanning capabilities, therefore compromising a key strength of the ETL. Subsequently, these optical simulations have been confirmed practically by imaging a dot checkerboard target using an ETL setup at driving currents of 0 and 250 mA (Qu and Hu, 2019). Configuration 1 yields a 20.6% difference in magnification across an axial scanning range of 3.540 mm when driving the ETL with 0 and 250 mA, while also exhibiting a degraded image resolution.…”

Design and Development of an Automated Dual-Mode Microscopic System Using Electrically Tunable Lenses

“…Many researches have proposed several techniques separately for optical zooming (Lin et al, 2011; Li et al, 2016; Iwai et al, 2019; Sanz et al, 2020) and to maintain the telecentricity while imaging axially with ETL (Matrecano et al, 2014; Qu & Hu, 2019). In their earlier work, authors have also presented a solution of maintaining a telecentric image plane by utilizing a variable numerical aperture controller with the objective (Barak et al, 2021 b ).…”

Large zooming range adaptive microscope employing tunable objective and eyepiece

“…Due to lightweight, low power consumption and fast response speed, liquid lenses have important applications in imaging 8 – 10 , display 11 , and communication 12 . Moreover, liquid lenses are wildly used in microscopy as focusing component for axial scanning 13 – 16 , increasing the depth-of-field 17 , 18 and autofocusing 19 , 20 . However, they cannot achieve continuous zoom change.…”