Determining field of view: The actual field of view of an eyepiece roughly equals its apparent field (the angular diameter of the circle of light you see in the eyepiece when you look through it by itself) divided by the magnification provided by the telescope and eyepiece combination. For example, if a 50° apparent field eyepiece gives you 100x on a particular telescope, it will have a 1/2° actual field of view (50/100) - about the diameter of the full Moon.