Calculating Telescope Magnification Detailed Explanation

Calculating telescope magnification is simple: Divide the telescope’s focal length by the eyepiece focal length, in millimeters.

Calculating Telescope Magnification needs a proper understanding of the different terms used in Telescope calculations. Let’s look at some important terms.

• Scope Aperture-this is the diameter of the lens or mirror
• Scope Focal Ratio (f/number)-Focal length divided by aperture
• Barlow Lens- this is a lens that is placed into the focusing tube to increase the telescope’s focal length
• Focal Reducer- this is a device used to shrink the focal length of the telescope.

Telescope Calculator Results

1. 1. Focal Length-is the distance from the lens or mirror to the image formed
   2. Magnification – is the level of enlargement of the image on the telescope . Its focal length divided by the eyepiece’s focal length.
   3. True Field of View-the circle of the sky that you see when you see through the telescope
   4. Exit Pupil-this is the size of the circle of light hitting the eye when you look through the eyepiece

Factors that Affect Telescope Magnification

• Seeing conditions: these are mostly weather conditions and light pollution which distorts the image. In such cases reduce the magnification
• Size of the Object- every object is different on a telescope depending on its size, for bigger objects use a lower magnification.
• The focal ratio- The longer the focal length the greater is the magnification and the narrower is the field of vision.
• Telescope resolution-Better resolution power makes images clear

Calculating telescope magnification for a Celestron Scope

Magnification for a Celestron Scope

Magnification= Length of Telescope (mm) divided by Length of Eyepiece (mm)

Magnification = Telescope focal length ÷ Eyepiece focal length

For example, if you have a 1000mm focal length telescope with a 25mm eyepiece, the magnification will be 40x (1000mm ÷ 25 = 40).

Remember :

• Never look through window glass, it affects the focus of the telescope
• Hazy skies, fog, and mist will affect your telescope results

See Also