Design Method Of Extreme Simplified Zoom System With Wavefront Coding

In order to improve the imaging performance,modern optoelectronic imaging system usually use more lenses to correct optical aberration.When the zoom function is needed,the structure will be more complex: To change the focal length of the system and keep the image plane stable when zooming,the system requires multiple lens groups to move axially in accordance with certain rules.In the meantime,a precision machined CAM mechanism is needed to control the accurate movement of multiple lens groups to ensure the smooth zoom process.As a result,zoom lenses are usually more complex,bulky,and heavier than prime lenses.In order to simplify the zoom system,this thesis developed an optic-digital hybrid zoom system design method.With the coding phase surface,the image drift can be compensated,which was caused by the movement of the zoom group in the zooming process,and a series of intermediate coded blurred images are generated.After decoding the blurred images through the image restoration algorithm,a clear visual image can be obtained.The coding surface can replace the compensating lens group in the traditional zoom system and cancel the use of CAM mechanism,and finally reduce the structural complexity of the zoom system.Major contents of this thesis include the following parts:(1)Based on the theory of wave-front coding technology and the derivation of the relationship between the maximum image drift of the optic-digital hybrid zoom system and system parameters,the feasibility and effectiveness of the wave-front coding element compensating the image drift of the zoom system are preliminarily verified.(2)On the basis of previous optimization methods of wavefront coding system,a global optimization evaluation standard of optical-digital hybrid system is proposed,which can balance optical aberration,MTF consistency with defocus and detector noise.This optimization criterion uses the system data calculated by optical software,so the calculation speed is fast and it is easy to be implemented in commercial optical design software.(3)A three-piece optic-digital hybrid zoom lens is designed using the developed method.In comparison,a four-piece mechanical compensation zoom lens is designed under the same parameters.The imaging performance of the two systems demonstrates the ability of the optic-digital hybrid zoom system design method to simplify the zoom system.In this thesis,the feasibility and effectiveness of a zoom system design method are proved by the theoretical analysis,detailed description and verification of the method.Results show that the optic-digital hybrid zoom system can achieve imaging quality comparable to the traditional complex zoom structure using a simpler system structure and fewer lenses.This method can be used to design zoom system with low zoom ratio,which can reduce the structure complexity of the zoom system,the workload of designers,also the volume and weight,etc.