Yi-Chin FANG, Chen-Mu TSAI^1*, Wei-Teng LIN, and Yu-Cheng LIN

Department of Mechanical and Automation Engineering, National Kaohsiung First University of Science and Technology, 2 Jhuoyue Road, Nanzih District, Kaohsiung 811, Taiwan, R.O.C.
¹Department of Computer and Communication, Kun Shan University, No. 949, Da Wan Road, Yung-Kang, Tainan Hsien 710, Taiwan, R.O.C.

(Received January 20, 2007; Accepted August 10, 2007)

In today's digital age, digital projectors and their application are gaining in significance, especially in the home theater area where the projected area is more than hundred inches. More attention has to be paid to the design of these than of ordinary data projectors due to the enhancement of both definition and contrast for home theater projectors. This complicates the optical design of the projector, especially in 1080 P flat plane panel resolution requirements with strong offset of 130%, whose semi-image height (18.6 mm) is very close to that of 35 mm film (20 to 21 mm). In this paper the lens design samples focus on the application of a projector with a 1080 P digital micromirror device (DMD) system with 10.68 μm per pitch. Such lenses have the telecentric design on the image side because of the total internal reflection (TIR) prism. The complicated design is the reason for this: firstly, there must be a very long back focal length due to the huge TIR prism and zoom mechanical system; secondly, there is an extremely relative luminance requirement (70% minimum) at semi-image height (18.6 mm); thirdly, there are difficulties in the elimination of lateral aberration due to the limited choice of glass and, fourthly, there is a 2× zoom ratio with modulation transfer function requirement of 40% at 50 lp/mm at a semi-image height of 18.6 mm minimum and, most important, limited total overall length. The lens design with 2× zoom ratio for 1080 P resolution was presented with great success; the optimal calculation of lateral chromatic aberration via genetic algorithm (GA) was introduced in this research and then a local minimum of lateral color aberration was identified.

Key words: optical design, genetic algorithm, HDTV, TIR prism, lateral chromatic aberration, 1080 P resolution, MTF

^*Corresponding author. E-mail address: jmutsai@mail.ksu.edu.tw