根据微型纤维软镜小尺寸、大视场的要求,分析其设计准则,采用“负-正”型反远距物镜作为初始结构,确定其为像方远心光学系统。通过理论计算和Zemax光学仿真软件的不断优化,最终设计出了一个工作波段在0.48 μm ~0.65 μm,焦距为0.37 mm,全视场90°,相对孔径为1∶4的微型光纤传像束内窥镜物镜。该物镜由4片透镜组成,包括1片负透镜、1片正透镜和1片双胶合透镜。设计结果表明：镜头总长3.89 mm,最大横截面直径0.95 mm,满足像方远心光学系统的初始设计要求,在奈奎斯特空间频率77 lp/mm处的调制传递函数(MTF)近似为0.7,接近衍射极限,并且具有小尺寸、大视场、像质优良、结构合理、像面光照强度均匀等特点,符合微型纤维式内窥镜的使用条件。

According to the requirements of small size and large field of view(FOV) for subminiature fiber soft endoscope, the fundamental design criteria was analyzed, the retrofocus objective with a “negative-positive” form was utilized as the initial structure, and the telecentric optical system in image space was determined for this design.Through theoretical calculation and continuous optimization with Zemax optical design software ,a designed subminiature endoscope objective lens sample was fabricated finally, with operation wavelength,focal length, FOV and relative aperture of 0.48 μm~0.65 μm, 0.37 mm, 90° and 1∶4, respectively.The optical system is composed of 4 pieces of lenses, including two single lenses and one cemented doublet.The result shows that its total length is 3.89 mm and maximum cross sectional diameter is 0.95 mm,which can satisfy the initial design requirements of image telecentric structure.The modulation transfer function (MTF) value of the lens is approximately 0.7 at Nyquist spatial frequency of 77 lp/mm,near the diffraction limit. Furthermore, the designed lens has the peculiarity of wide FOV, short focal length, fine quality of imaging, reasonable structure and uniform illumination at image plane. It is suitable for the subminiature fiber endoscope demand.