Key techniques for extending the depth of field of optical imaging system
MO Xu-tao,LIU Wen-yao,WANG Jin-jiang ( Opto-electronic Information Science and Technology Laboratory of MOE, College of Precision Instruments and Opto-electronic Engineering, Tianjin University, Tianjin 300072, China )
The depth of field of standard optical incoherent imaging system can be extended by introducing a phase plate and the digital image restoration technique. A novel circular pure phase plate is developed,which is divided into several annular equal-area zones. The zones alternately eliminate the influence of defocusing beside the Gauss image plane. The Modulation Transfer Function (MTF) curves of system and MTF density map confirm the defocus-invariance of the system with the plate. Also the related focus-independent image restoration filter is introduced based on the frequency domain filtering theory and the defocus-invariance of the system. The simulated Spoke images on different defocuses verify the Extended Depth of Field (EDF) of the system. The EDF of the new system with the plate is over 4 times greater than that of the original system by adjusting the parameters of the plate. The system can be used in the fields of biological and medical micrology, machine vision, etc.
【CateGory Index】： O438