Your Telescope Magnification  =  Barlow     x   Focal Length of telescope    /    Eyepiece 

Barlow lens = It is usually in the range of 1.5x to 3x. The most common is 2x. So a 2x Barlow will double the power of your eyepieces.

Focal length = the distance in millimeters between the telescope's primary lens or mirror and the point where the light rays come together in focus. Some telescope ads may show inches; just convert it to millimeters.

Eyepiece = viewing the night sky requires more than one eyepiece. Choosing the correct eyepiece is very important so that it doesn't cause eye fatigue. As you will see, eyepieces are very expensive. The small eyepieces that come with your telescope are normally subpar and cannot be used.

 Use the chart below to get a sense of what your telescope's magnification is. Not all magnifications below will be viewable due to many factors. If your telescope focal length is 660, 500, or 900 mm and depending on the Barlow used, the charts below will help you get the magnification. With all others, just use the simple formula.