lens opening meaning in English

镜头开度
镜头孔径
透镜孔径

He was always forgetting to put film in the camera or turn on lights or remove the cover from the lens opening .
他不是忘记装胶卷，打灯光，就是忘记揭开镜头盖。
So what is the ideal shape for the lens opening
因此光圈理想的形状是怎样呢？
Figure 4 : here ' s the test target as photographed with an upwards pointing triangular lens opening and with the film too close to the lens
图三：一些简单的黑白的测试图样，用于判定光圈形状对失焦图像的影响。