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Message: <blockquote data-quote="typo" data-source="post: 3346625" data-attributes="member: 83808">Those numbers work out quite nicely. To read a 5cm number you will need to be able to see detail at about 1.5cm. At one kilometer, 1.5cm subtends an angle of 3 arcseconds. The Dawes limit for a 50mm objective is 2.34" so a high quality objective should should be just about sufficient. My own 50mm scope I estimated at 2.4" and it sounds like your Nikon must be comparable. If your eyesight is a typical 6/4.5 (20/15) or 90 arcseconds you would need 90/3 = 30×  to read it. Your 23x eyepiece most likely wouldn't be sufficient as you imply , but the 27x might just do the trick.I also have a 60mm scope which has a relatively poor 3.5" resolution and would probably fail your test as well.David</blockquote>