Extending the depth of field (DOF) is especially essential in thick and 3D sample imaging. However, it's difficult to achieve both large DOF and high resolution in a zoom microscope. Currently, the use of optical sectioning to expand DOF still has the problem of inconstant magnification. Here, we develop an extended the depth of field (EDOF) and zoom microscope, which can realize EDOF with constant magnification and high resolution. Besides, the proposed microscope can achieve optical axial scanning at different NA and magnifications in real time without any mechanical movement. The proposed varifocal lens is employed to realize optical axial scanning, zooming, and keeping constant magnification when extending the DOF. Experimental results show that the proposed microscope can realize a continuous optical zoom of 10–40×, NA from 0.14 to 0.54, and the DOF of microscope can be extended to 1.2 mm.

We propose a zoom liquid lens employing a multifocal Fresnel zone plate. The proposed lens has two optical surfaces: liquid-liquid interface and Fresnel zone plate. The Fresnel zone plate is designed to have a multifocal point and an increased depth of focus. Therefore, the proposed lens has two obvious advantages. Due to increased depth of focus, the proposed lens can realize zooming using only one tunable liquid-liquid interface, which is not available for conventional liquid lens. Thus, it is possible to remove conventional zooming mechanisms from cameras. Besides, the focal length tuning range is also increased, and a lens system based on the proposed lens can simultaneously collect two images with different magnifications. We present the design, fabrication and characterization of the proposed lens. The shortest positive and negative focal length are ∼17.5mm and ∼−34.5mm and the diameter is 5mm. The zoom ratio of the proposed lens reaches ∼1.48×. Our results confirm that the proposed lens has widespread applications in imaging system.

The conventional microscope has discrete magnification and slow response time in zoom process, which is difficult to capture the dynamic activity of the live specimen. We demonstrate an adaptive microscope employing a tunable objective and a tunable eyepiece with large zooming range. The tunable objective consists of three glass lenses and four electrowetting liquid lenses. The tunable eyepiece consists of an achromatic eyepiece and an electrowetting liquid lens. The focal point between the objective and the eyepiece is designed to be tunable, which are controlled by voltages. Thus, the tuning range is relatively large. We fabricate the adaptive microscope and observe the specimen. In the experiment, the magnification of the microscope changes continuously from ~ 59.1 × to ~ 159.2 × , and the largest numerical aperture is ~ 0.212. The tunable eyepiece can release the back focal length of the tunable objective, which increases the zoom range of the microscope. No mechanical movement is required and the aberrations can be corrected over a wide wavelength range. Thus, the proposed adaptive microscope has a potential application in biological research and clinical medical examination. Microscopes play an important role in scientific research and production, such as physiological applications 1 , biomedical engineering 2 and microfabrication 3. For targets of different sizes, microscopes need different magnifications. Besides, to observe large area of cells and a zoom-in area with high resolution, the higher requirements of real-time observation and continuous zoom change on microscopes emerges 4. The conventional microscopes can change magnifications by manually converting objectives. But its magnifications are not continuous and the conversion operation introduces sample vibration. One of the solutions for continuous zoom change is to use the mechanical or optical compensation system driven by mechanical movement 5,6. However, such compensation systems are bulky and sample vibration is still an issue due to the mechanical movement. Besides the slow zoom speed affects the real-time observation. Fortunately, the liquid lenses have changed the traditional lens systems 7. 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. For example, a five-dimensional microscopy using liquid lens is proposed and able to scan volumes rapidly and reproducibly 21. This microscopy has fast scan speed however it cannot zoom continuously. A adaptive microscope objective using liquid lens is proposed 22. The magnification of the adaptive microscope objective tune from ~ 7.8 × to ~ 13.2 × , but its zoom range is very limited due to fixed back focal length (BFL). Therefore, it is still urgent to study microscopes with larg...