基于球面透镜的超短焦投影系统设计

Design of Ultrashort Focal Projection System Based on Spherical Lens

为了实现大像面、小投射比、高清画面要求,设计了一款折反式超短焦投影镜头。根据性能指标要求选择了反远距系统,采用缩放法获得初始结构,由出瞳位置不同视场光线与像面的高度关系,计算获得了反射镜坐标数据,拟合得到反射镜面型。采用点列图、场曲/畸变和调制传递函数(Modulation Transfer Function,MTF)曲线对像质进行了评价。最终获得了焦距为5.45 mm,投射比为0.4的物方远心系统,在投影距离720 mm时可投射80 inch画面,清晰度为1080 p,视场角为136°,放大倍率约为125倍,系统点列图均方根(Root Mean Square,RMS)半径小于750μm,畸变小于0.2%,相对照度在96%以上,其MTF曲线幅值在0.54 lp/mm时均大于0.3。公差分析表明,系统设计合理,成像质量良好。相较于其他折反式超短焦投影镜头,该系统在保证成像质量的同时折射部分未使用非球面,有效降低了加工和装配难度。

In order to achieve the big image plane,small throw ratio,high definition picture requirements,a catadioptric ultra-short focal projection lens is designed.According to the requirements of performance indicators,the inverse telescopic system is selected,and the initial structure is obtained by the scaling method.The mirror coordinate data is obtained by calculation from the relationship between the light rays of different fields of view and the height of the image plane at the exit pupil position,and the mirror surface type is obtained by fitting.The image quality is evaluated by using point plot,field curve/distortion and modulation transfer function(MTF)curve.Finally,an object-space telecentric system with a focal length of 5.45 mm and a throw ratio of 0.4 is obtained.When the projection distance is 720 mm,it projects an 80 inch screen with a resolution of 1080 p,a field of view of 136°,and a magnification of about 125 times.The RMS radius of the column diagram is less than 750μm,the distortion is less than 0.2%,the relative illuminance is above 96%,and the MTF curve amplitude is greater than 0.3 at 0.54 lp/mm.Tolerance analysis shows that the system design is reasonable and the imaging quality is good.Compared with other catadioptric ultrashort focal projection lenses,the system can ensure the imaging quality without using aspherical surface in the refraction part,which effectively reduces the difficulty of processing and assembly.