f number meaning in English

焦距比数

Load the high speed film , open the lens to its lowest f number and focus at infinity . select b for the shutter setting . mount the camera on a tripod and aim it at the desired region
用广角镜或标准镜的相机，装上快速底片，光圈全开，镜头调至无限远，快门选b掣，用脚架支持相机指向欲摄的天区，用快门绳打开快门，曝光几分钟到一小时的固定摄影法，会把偶然出现于镜头前方的流星摄入底片。
The following results are obtained : ( 1 ) the flow in rotating helical pipes are affected by dean number , curvature , torsion ( or germano number ) , the ratio of the coriolis force to the centrifugal force f number ( or rossby number ) and the geometry of the cross section
研究结果表明： ( 1 )旋转螺旋管道流动特性受dean数、曲率、挠率(或germano数) 、科氏力与离心力之比f数(或rossby数)以及截面的形状五种因素的影响。