We discuss the design, manufacturing and characterization of a miniaturized zoom camera objective featuring two gravity-immune liquid-tunable aspherical lenses and three spherical glass lenses. The aspherical tunable lenses, which are 3 mm in diameter, 8 mm in nominal focal length and neutral to gravity effects, can be pressuretuned within a large focal length range with very low spherical aberration. This leads to high optical resolution across the entire zoom range despite the limited number of optical elements in the system. The effective focal length of the objective continuously shifts from 4.5mm to 9 mm, with the field of view changing from 40° to 20°. All the optical components are assembled on a three-layer optical platform, which provides a lateral and axial positioning accuracy of ±10 µm for all components. Furthermore, the platform also maintains fluidic access to the tunable lenses for pressure tuning via an external pressure controller. The total dimensions of the objective are 5 mm×6.5 mm×17 mm, making the system compatible with mobile imaging applications. The highly compact system with the thickness of 6.5mm was achieved by folding the optical path using a 45° mirror. The optical performance of the system is characterized across the entire zoom range through imaging measurements.
We discuss the design, realization, and characterization of a miniaturized focus-tunable camera objective featuring a gravity-neutral, liquid-tunable aspherical lens and compare its performance to an equivalent system optimized for a conventional tunable lens. In addition to the innovative component, the objective design features three fixed elements and an aperture, which are all assembled to form a 5×5×13 mm system. With an image sensor size of 3 mm, the objective provides a viewing angle of 40 deg. By tuning the lens in its gravity-neutral range, the object distance can be shifted from 5 mm to infinity, with image-side cutoff frequency remaining above 84 lp/mm across the entire range. Through ray-tracing simulations and experimental results, we demonstrate that for optical trains of identical complexity, tunable aspherical lenses provide substantially better imaging quality over the object distance range of interest, compared to conventional, spherical tunable lenses.
A miniaturized adaptive-focus camera objective featuring a gravity-immune liquid-tunable aspherical lens is presented. The lens, which has an aperture size of 3 mm, a nominal focal length of 8mm and an optimum tuning range between 7.2 to 8.8 mm, is experimentally demonstrated to have diffraction-limited performance at the nominal focal length with identical performance for vertical and horizontal lens orientations, leading to a drastic reduction in spherical aberration compared to conventional liquid-tunable lenses. The camera objective comprises three fixed elements and a tunable lens, arranged on a 5×5×13 mm platform. It provides a viewing angle of 40° imaged on a 3 mm sensor. By tuning the lens in its optimum operation range, the object distance can be shifted from 5mm to infinity.
Continuous optical zoom is an enabling feature for an endoscopic microscope system combining high resolution and large field-of-view (FOV) imaging. Conventional zoom systems utilize translating lenses to achieve optical zoom, but this further reduces the already narrow optical aperture available in the endoscopic probe. Liquid-tunable membrane lenses combine the actuator and optical aperture, and thus allow an efficient use of the available aperture. However, currently, such lenses suffer from significant spherical and other optical aberrations. In this paper, we present a miniaturized continuous zoom microscope design with an optical aperture of 1mm featuring two liquid-tunable aspheric lenses for optical zoom and two fixed lenses for aberration and color dispersion correction. The liquid-tunable aspherical lenses are formed by liquid reservoir sealed with a PDMS membrane of non-uniform thickness. A systematic approach to identify the membrane thickness profile yielding a desired deflection shapes also discussed. The continuous magnification range of the zoom system is from 1.5 to 3.5 using a 1×1mm CCD as the imaging element. With an object distance smaller than 3mm, the total length of the system is less than 9mm. We demonstrate that with the introduction of the aspherical tunable lenses, the optical performance of the zoom system is considerably improved. Keywords: Zoom optics, endomicroscopy, liquid-tunable lenses, aspherical microlenses.