单词focal-ratio
网络: 焦比；焦距比；焦比大
Or, you can calculate the exit pupil by dividing the focal length of the eyepiece (in mm) by the focal ratio of the telescope.
或者，你还可以将目镜的焦距除以望远镜的焦比来得到出瞳尺寸。
If you know the focal ratio but not the focal length, you can calculate it: focal length is the aperture (in mm) times the focal ratio.
如果你不知道焦距，只知道焦比（focalratio），你可以通过这样计算的得到焦距：孔径（单位是mm）乘以焦比就是焦距。