Determining magnification: The power of an eyepiece is found by dividing
the focal length of your telescope by the focal length of the eyepiece. For example,
a 20mm eyepiece on a 2000mm telescope (2000 , 20) gives you 100 power (100x). This makes objects
appear 100 times closer to you through the telescope than they appear to your unaided
eye. The same 20mm eyepiece on a 1000mm focal length scope (1000 , 20) gives you 50x.
The longer the telescope focal length, or the shorter the eyepiece focal length,
the higher the power – but the dimmer the image.