Optical design of zoom projection lens

Zoom projection lens are designed to meet requirements of different screen size with same optical engine and screen position. Focal length of zoom projection lens ranges from 22 mm to 37 mm, viewing angle is 46° to 75°, and F number is 2.8. Considering design of optical system requiring a relatively large aperture, with large field of view and small zoom ratio, according to zoom theory, positive mechanical compensation configuration is adopted, reasonable magnifications of zoom configuration are chosen and Gauss roots are derived. Appropriate primal configurations based on each subassembly are chosen. Optimization design is carried out with Zemax optical design software, and added proper aspheric surface. Mechanical compensation method of two and four component motion is used to solve problem that distortion of large field of view is difficult to control, and whole optical system is evaluated synthetically by using modulation transfer function (MTF). Design results show that optical structure and image quality of zoom projection objective system meet design requirements. Spatial modulation transfer function (MTF) value is more than 0.3 at spatial frequency of 64 lp·mm^-1, and distortion is less than 1%.