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Focus Measure in a Liquid-filled Diaphragm (LFD) Lens Using Passive Auto-focus Metho - priyankameena - 08-16-2017 Abstract Auto-focusing in imaging systems depends on the determination of the correct image focus criterion. In this research, the image captured by a liquid-filled diaphragm (LFD) fluid lens was analyzed to determine a focus measure criterion that can be used to establish the correct focus and thus quantify the image quality. The LFD lens was actuated using a steppermotor driven syringe mechanism. The lens diaphragm was made of polydimethylsiloxane (PDMS) polymer that exhibit good optical properties. The lens focal length was controlled by varying the fluid volume within the diaphragm lens. A CCD camera was attached to the fluid lens to capture live images of a binary target. The edge slope width (ESW) of the pixel intensity profile across the white-to-black transition region in a binary target was used as the focus measure. The experiments carried out showed the viability of the proposed focus measure criterion for automatically focusing the image formed by a diaphragmtype fluid lens. Keywords liquid-fill, diaphragm, lens, focus I. INTRODUCTION Optical devices such as cameras, microscopes and other imaging systems use various types of variable focusing mechanisms that have been developed in the past. The conventional methods of varying the lens focal length, i.e. by using motors, slides and gears, is still widely used in most imaging systems. The main disadvantage of the conventional focusing mechanism is that it requires several interlinking mechanical components. The inherent contact-friction subjects these components to wear, thus affecting the focus quality of the captured images. Since there is a general advancement towards making smaller cameras and imaging systems, accommodating the various moving parts in the conventional focusing mechanism faces space and manufacturing constraints. Therefore, a new focusing mechanism with fewer moving parts is required for enhancing the performance of optical devices. Fluid lenses have great potential for replacing the traditional glass lenses in achieving variable focusing. In a fluid lens system a single lens changes its shape continuously to achieve varying focal lengths, similar to the human eye. In one popular design of the fluid an elastic transparent diaphragm that is pressurized by an optically transparent fluid lens ise used to achieve variable focusing. The fluid pressure causes the diaphragm to produce various curved profiles, thus resulting in continuously varying focal lengths. Unlike the conventional variable focal length lenses (such as a zoom lens) where the distances between multiple lens elements are varied, the fluid lens accomplishes variable focusing using a single lens. Because of this significant advantage of the fluid lens compared to a glass lens, a number of studies relating to diaphragm-based liquid-filled lenses have been undertaken in the past. Shaw and Sun [1], studied the optical properties of different liquid-filled fluid lenses to obtain the best membrane shape. The effect of diaphragm clamping boundary conditions, diaphragm thickness and diaphragm cross-section shape were studied using a non-linear finite element method. Shaw and Lin [2] designed and analyzed an asymmetric diaphragm type fluid lens. By controlling the tilt angle of a pressure ring it was possible to control the light direction or the focal length. Zhang et al. [3] developed a variable focus zoom lens on a chip with a wide field-of-view tuning range using the standard microfabrication process. The lens was characterized using an array of LEDs as the object, placed at a fixed distance from the lens. Ahn and Kim [4] proposed a crystalline human eye s lens-like variable focusing lens using square glass diaphragms. The square boundary conditions, however, causes the deflected diaphragm to take a cushion-like shape and thus introduce distortions in the image. Several other researchers have looked into various aspects of the fluid lens, such as lens on a microfluidic chip [5-7] and obtaining high zoom ratio and wide tuning range [8]. Several authors used various types of actuation mechanisms for the LFD lens to change the lens focal length. For instance, Gunasekaran et al. [9] used a syringe pump to actuate the fluid lens, Kuwano et al. [10] implemented a stepper motor driven syringe mechanism to change the liquid pressure inside the lens, Ren et al. [11] used a servo motor to squeeze an elastic rubber membrane wrapped around the fluid lens, thus varying the pressure within the lens and Lee et al. [12] developed a fluid lens that was tuned using an electro-magnetically actuated diaphragm pump attached to the main lens chamber. Shaw and Lin [13] developed a novel method to actuate the diaphragm lens by pressurizing an O-ring attached to the fluid lens. A thermal-based fluid actuation for a diaphragm micro-lens of 1.9 mm diameter Download full report http://googleurl?sa=t&source=web&cd=2&ved=0CCIQFjAB&url=http%3A%2F%2Fieexplore.iee.org%2Fiel5%2F5702939%2F5707203%2F05707235.pdf%3Farnumber%3D5707235&ei=dWMlToicJISrrAfi3pinCQ&usg=AFQjCNFZWudH7QrJ-6-QWqiKwRsDHX7QSg&sig2=V_rUeyVejSMCaJrsFBrx0g |