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对近贴聚焦的双平面透镜、锐聚焦的静电透镜和电磁透镜的调制传递函数(MTF)作了推导和介绍。可以证明对于麦克斯威尔发射能量分布来说,双平面透镜的调制传递函数为:MTF=exp(-4π~2∈/V_3L~2df~2)。式中:L为荧光屏到光阴极之间的距离,以毫米计;f为空间频率,以线对/毫米计;V_3为荧光屏上的电压,而∈是最可几发射能量的等效电压。对于余弦分布来说,双平面透镜的MTF为:MTF=exp(-7π∈/V_3L~2f~2)。锐聚焦象管透镜的MTF为:MTF=exp(0.06π~2∈~2M~2f~2/E_c~2)。式中:E_c是光阴极的电场强度,以伏/毫米计;M是放大倍率。象管透镜的MTF一般可以表示为MTF=exp[-(πρf)~2],式中ρ是实际透镜的聚焦误差系数(focusing error coefficient)。
The modulation and transfer function (MTF) of near-focusing biconvex lens, sharp focusing electrostatic lens and electromagnetic lens were deduced and introduced. It can be shown that for the Maxwell emission energy distribution, the modulation transfer function of the biplane lens is: MTF = exp (-4π ~ 2∈ / V_3L ~ 2df ~ 2). Where L is the distance between the screen and the photocathode in millimeters, f is the spatial frequency in mm / mm, V_3 is the voltage on the screen, and ∈ is the equivalent voltage of the most energetic emission. For the cosine distribution, the MTF of the bi-planar lens is: MTF = exp (-7π∈ / V_3L ~ 2f ~ 2). The MTF of sharply focused tube lens is: MTF = exp (0.06π ~ 2ε ~ 2M ~ 2f ~ 2 / E_c ~ 2). Where: E_c is the electric field strength of the photocathode in volts / millimeter; M is the magnification. The tube lens MTF generally can be expressed as MTF = exp [- (πρf) ~ 2], where ρ is the actual lens focusing error coefficient (focusing error coefficient).