2018年USAAAO短问题第5道
来自astro-init
英文题目
5. [5 pt] An amateur astronomer observes the Moon with 20-cm telescope, and accomplishes 160x magnification with an eyepiece with focal length 10 mm. What is the f-number of the telescope?
5. [5 pt] An amateur astronomer observes the Moon with 20-cm telescope, and accomplishes 160x magnification with an eyepiece with focal length 10 mm. What is the f-number of the telescope?