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This paper presents a motion-free technique for characterizing the focallength of any spherical convex or concave lens. The measurement system uses aGaussian Beam from a Laser Source (LS), an Electronically Controlled VariableFocus Lens (ECVFL), a Digital Micromirror Device (DMD) and a Photo-Detector(PD). As the proposed method does not involve any motion-stages or other movingcomponents, the focal length is measured without requiring any mechanicalmotion of bulk components. The method requires measuring the spot size of theGaussian Beam at the DMD plane for various settings of the ECVFL focal length.These beam spot size measurements, are used to estimate the focal length of alens sample by employing standard polynomial-fitting techniques. Due to theinherent motion-free nature of the proposed setup, the measurements are fast,repeatable, reliable and ideal for use in industrial lens production,manufacturing of imaging systems and sensitive laboratory experiments. Using aDMD and an ECVFL also allows for automating the lens characterization process.As a proof-of-concept, experiments were performed to determine focal lengthvalues of multiple lens samples with the proposed technique. The values offocal lengths of all samples are in agreement with the focal length valueswhich were provided by the manufacturer of these test lenses. The estimatedfocal length values are within the 1% manufacturing tolerance values that wereprovided.

A Technique to Measure Focal Length of a Lens with no Bulk Motion using Tunable Optics and Optical MEMS Technology