| Modern optical system is mainly characterized by its compactness, light weight, low cost, high reliability. With the enhancement of design, processing and testing technology, optical aspheric surface has gradually become one of the most popular components. Imaging quality and compactness of optical system can be effectively improved with an aspheric surface being included in the proper position. As the development of material technology, optical plastics with excellent optical and mechanical performance have been produced in recent years. Such Optical plastics are suitable for massive production and have the advantages of low cost,, light weight and impact resistance.This paper firstly introduces the development history and current situation of digital camera. The performance requirements and the choice of lens type for our digital surveillance camera are analyzed. The basic principles of its aberration correction with aspheric lens are described. The optical and mechanical performances of common optical plastics and the processing method of plastic aspheric lens are analyzed and compared.Then, a mini lens composed of four pieces of singlet for digital surveillance camera is designed. During its optimization, a dual aspherical lens made from 480R optical plastic material, which has excellent optical and mechanical performances, has been used to correct its aberration effectively. The designed lens has 1:2 of relative aperture, 7.11mm of focal length, and 46.4°of full field of view. And its relative distortion is smaller than 2%, its MTF value greater than 0.3 at 80 lp/mm spatial frequency. The imaging quality of the designed lens meets its performance requirements. Its tolerance is comprehensively analyzed for account of the influence of the cooling and solidifying process during the injection molding of plastic lens on its surface profile. The analysis shows that its tolerance is relatively reasonable and fits with practical manufacture. |
