Comparison of a grating optical lowpass filter with a birefringent filter

摘要

The characteristic of two-dimensional grating optical low-pass filter (GOLDF) was compared to that of birefringent low-pass filter (BLF). The modulation transfer function(MTF) of the optical system that consists of lens and GOLF is theoretically derived by taking all orders of diffracted beams into consideration. MTF of a 2 phase chess-board type GOLF and a 3-phase GOLF was compared to that of BLF. The 3 phase GOLF with 9 center beams of equal strength has the best filtering characteristic, and thus removes most moire fringe, but resolution degradation is severe compared to BLF. The two-phase GOLF with phase difference of 180° that is similar to BLF in term of beam distribution has medium characteristic of 3-phase GOLF and BLF. And, 3 phase GOLF of phase difference of 90° has similar characteristic, too. these three GOLF's are made and experimented by attaching them to a digital camera. The experimental result coincides with the theoretical development.