The continuous zoom system with a large zoom ratio can search for a target in the wider field-of-view and distinguish a target at a further distance. As the range of focal length is limited for a traditional continuous zoom system, we present a compound zoom method to greatly increase the range of focal length for a traditional continuous zoom system. The compound zoom method combines the traditional zoom system with a dual field-of-view zoom system to achieve a large zoom ratio. The differential equation model of the compound zoom method is established. Based on this model, a long-wave infrared zoom system with a zoom ratio of 36 and F/1.6 is designed, and it has such advantages as large zoom ratio, simple mechanical structure, good image quality, and smooth cam curves.
In order to get three-dimensional distribution of the optical material which has very high index homogeneity, measuring index homogeneity of the main direction of a sample, then opening a rectangle window in the sample to measure the index homogeneity of the window direction. Zernike circle polynomials are in widespread use for wavefront analysis because of their orthogonality over a circular pupil and their representation of balanced classical aberrations, for the main direction is circular, we use the Zernike circle polynomials to fit the main direction interferometric data. From result of fitting the main direction interferometric data, we find the measuring error which must be taken into account. So it is an important question how to choose the orthonormal polynomial for fitting the window direction interferometric data. Using the Zernike circle polynomials as the basis functions, the orthonormal polynomials of the rectangular pupil be obtained from the circle polynomials by the Gram–Schmidt orthogonalization process, using the first fifteen items of the orthonormal polynomials of the rectangular pupil fit the interferometric data of the window direction, we get a good fitting precision, find the measuring error of some samples considerable at the same.