2018年USAAAO短问题第5道
来自astro-init
Jingsong Guo（讨论 | 贡献）2020年3月9日 (一) 18:13的版本 （创建页面，内容为“==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 m…”）
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?
