Computation of Analytical Zoom Locus Using Padé Approximation

When the number of lens groups is large, the zoom locus becomes complicated and thus cannot be determined by analytical means. By the conventional calculation method, it is possible to calculate the zoom locus only when a specific lens group is fixed or the number of lens groups is small. To solve this problem, we employed the Padé approximation to find the locus of each group of zoom lenses as an analytic form of a rational function consisting of the ratio of polynomials, programmed in MATLAB. The Padé approximation is obtained from the initial data of the locus of each lens group. Subsequently, we verify that the obtained locus of lens groups satisfies the effective focal length (EFL) and the back focal length (BFL). Afterwards, the Padé approximation was applied again to confirm that the error of BFL is within the depth of focus for all zoom positions. In this way, the zoom locus for each lens group of the optical system with many moving lens groups was obtained as an analytical rational function. The practicality of this method was verified by application to a complicated zoom lens system with five or more lens groups using preset patents.

Non-Destructive Measurement of Doublet Objective Lens Structure Parameters Based on ZEMAX

A method for structure parameters of doublet objective lens with non-destructive measurement is proposed based on the ZEMAX software. The focal length, back focal length, central thickness and the radius of curvature of the first surface and last surface are measured by a spherical interferometer and other instruments. Using the inversion of the evaluation function and optimizing of the ZEMAX, the series of refractive index of the materials and the cemented surface of the doublet objective lens are derived. Then the optimal combination of the glass materials is selected by the aberration tolerances of the doublet objective lens. The examples show that the result is satisfactory.

An On-Line Digital Optical Bench Tester Based on Conoscopy for Lens Quality Evaluation

This study aims to develop an on-line tester machine for evaluating the image quality of a camera lens that is used in a lens module in a cell phone. This tester is not only suitable for conventional solid lens, but also applicable to the developing tunable liquid crystal lens by using the conoscopy approach to measure focus length and its quality. On the other hand, the approach using a commercial inspection chart along with a automatic feeding machine is also adopted for a quick estimate on the focusing quality that is primarily based on Modulation Transfer Function (MTF). In addition to the MTF, the proposed tester aims to has other functions of measuring Effect Focal Length (EFL), Back Focal Length (BFL), Field of View (FOV), Field curvature, Distortion, Astigmatism, Lateral/Axial Color, the distribution of index of refraction and phase retardation pattern. The constructed tester is capable of measuring varied optical performance indices for the next-generation tunable lens.