This is because an image can have a varying Blur Width (depth of field) and the subject which is to be in focus is usually in the center.
这是因为图像可能有不同的模糊边缘宽度(景深)和在该中心通常有需要聚焦的被摄物体。
The width, height, brightness of the screen and the luminous flux, focus of the cineprojector are important factors of cinema auditorium design.
银幕的宽度、挂高、亮度,以及放映机的光通量、焦距等都是电影观众厅设计的重要因素。
Keep your arms at shoulder width, and focus on feeling your fingertips move toward the far wall with each pulse.
双臂与肩同宽,注意体会每次蝶动时手指尖指向远方池壁滑水的感觉。