Here's an example: A 6-inch telescope has a focal length of 36 inches. To find the f/ratio, divide 36 by 6. This produces f/6. Often, the aperture is in inches, but the focal length is given in ...

The 18-inch telescope was erected on the open Observing Deck of the newly ... it was also equipped with a 4"x5" film holder, internal shutter, and 6" filter holder for large-format astrophotography.

The best telescopes allow you to observe this month's full planetary parade more closely and give you a front-row seat to the total lunar eclipse in March. The best telescopes unlock the wonders ...