"焦比"是个多义词，它可以指焦比（高炉炼铁技术经济指标）,焦比（光学系统焦距和光圈直径关系）。
快焦比的主要优点在于可以提供一个更宽的视角。
The main advantage of fast focal ratios with a telescope used visually is a wider field of view.
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。
Or, you can calculate the exit pupil by dividing the focal length of the eyepiece (in mm) by the focal ratio of the telescope.
当观察扩展光源时，目镜中所看到的亮度只跟孔径和放大率有关，它跟焦比并没有关系。
When viewing extended objects, the apparent brightness seen in the eyepiece is a function only of aperture and magnification, it is not related to focal ratio.
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