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Proceedings Paper

Optical design of an ultrashort throw ratio projector with two freeform mirrors
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Paper Abstract

In this work, an optical design approach is presented to design an ultrashort throw distance projection system by combination of an off-the-shelf refractive lens and two off-axis freeform mirrors. These two freeform mirrors are used to greatly shorten the projection distance by more than three times compared to conventional (rotationally symmetric) systems, while still maintaining a good imaging quality. Firstly, a direct design method that enables the simultaneous calculation of two off-axis freeform-profile mirrors by partially coupling more than three fields is introduced. The specifications of the conventional refractive lens are taken into account during this procedure. The pupil matching principle is applied to ensure good performance between the two sub-systems. The calculated mirrors then serve as a good starting point for optimization using commercial optical design software. To step from freeform profiles to freeform surfaces, the calculated two profiles are fitted into odd polynomials to evaluate the image quality and then re-fitted into XY polynomials for further optimization. Finally, the polynomial coefficients of the two freeform mirrors are imported into the optical design program. The merit function is built from RMS spot radii over the full field, and additional constraints are made for correcting distortion. After optimization, the calculated initial design quickly converges to a well performing imaging system. As an example, an ultrashort throw distance projection lens with a large 80-inch diagonal image at 400mm throw distance is designed, analyzed and compared with literature data. The values of MTF are over 0.6 at 0.5 lp/mm and the distortion is less than 1.5%: showing a very good and well balanced imaging performance over the entire field of view.

Paper Details

Date Published: 28 September 2016
PDF: 12 pages
Proc. SPIE 9947, Current Developments in Lens Design and Optical Engineering XVII, 99470C (28 September 2016); doi: 10.1117/12.2236613
Show Author Affiliations
Yunfeng Nie, Vrije Univ. Brussel (Belgium)
Rubén Mohedano, Light Prescriptions Innovators Europe, S. L. (Spain)
Pablo Benítez, Light Prescriptions Innovators Europe, S. L. (Spain)
Univ. Politécnica de Madrid (Spain)
Julio Chaves, Light Prescriptions Innovators Europe, S. L. (Spain)
Juan C. Miñano, Light Prescriptions Innovators Europe, S. L. (Spain)
Univ. Politécnica de Madrid (Spain)
Hugo Thienpont, Vrije Univ. Brussel (Belgium)
Fabian Duerr, Vrije Univ. Brussel (Belgium)


Published in SPIE Proceedings Vol. 9947:
Current Developments in Lens Design and Optical Engineering XVII
R. Barry Johnson; Virendra N. Mahajan; Simon Thibault, Editor(s)

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