focal length ratio

基本解释

For example, a telescope with a 2032mm focal length and an aperture of 8" (203.2mm) has a focal ratio of 10 (2032/203.2 = 10).
比如，望遠鏡的焦距爲2032mm，孔逕爲8英寸(203.2mm)，則它的焦比爲10 (2032/203.2 = 10)。
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，衹知道焦比(focal ratio)，你可以通過這樣計算的得到焦距：孔逕(單位是mm)乘以焦比就是焦距。
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，你還可以將目鏡的焦距除以望遠鏡的焦比來得到出瞳尺寸。