What does focal length mean?
Focal length is the distance (usually expressed in millimeters) from the telescope’s main optical element (main lens or primary mirror) to the point where light rays are brought to a focus. Focal length is important because it determines the magnifying power of the telescope. Magnifying power is calculated by dividing the focal length of the eyepiece (printed on the barrel of the eyepiece) into the focal length of the telescope.
