为满足场地规格略有不同的影厅的放映需求，基于机械补偿式的变焦思想，设计了一个四组九片式的变焦电影放映镜头，给出了凸轮曲线的设计方法以及光学镜头结构参量，并通过与一款经典35 mm变焦放映镜头结构的对比分析，阐述了该镜头的特点.镜头全部采用球面玻璃透镜，焦距为26~34 mm，视场角为36.2°~28.3°，相对孔径为1/1.7.系统总长为158 mm，全口径为71 mm.畸变保持在2%以内，在44.6线对/毫米的空间频率时，轴上调制传递函数高于0.68，轴外全视场的子午方向调制传递函数高于0.38，弧矢方向调制传递函数高于0.58.结果表明，本系统具有亮度高、像面稳定、结构紧凑、工艺性好等优点.

To satisfy the projection demand of cinemas with different size, based on mechanical compensation theory, a digital cinema projection lens is designed, and the cam curve is provided. The lens consists of four groups of nine glass lenses, and all the lens surface is spherical. Through comparing with the classical projection zoom lens, the character of the lens designed in the article is introduced clearly. Focal length is 26~28.3 mm, the relative aperture is 1/1.7, the total length is 158 mm, and the caliber is 71 mm. Distortion is less than 2%, at the frequency of 44.6 lp/mm, the axile MTF is higher than 0.68, the meridian MTF of the largest field is higher than 0.38, and the saggital MTF of the largest field is high than 0.58. The design results show that this lens has the merits of high brightness, steady image surface, compact structure and easy to process.