Telescope Magnification Calculator

Magnification determines how much larger an object appears through your telescope. The focal length ratio between telescope and eyepiece creates the magnifying effect. Additional calculations include exit pupil (brightness indicator) and true field of view (how much sky you can see).

1. 1

   Step 1

   Enter your telescope's focal length (found on the tube, e.g., 1200mm)

2. 2

   Step 2

   Enter your eyepiece's focal length (printed on the eyepiece, e.g., 25mm)

3. 3

   Step 3

   Optionally add aperture to calculate exit pupil

4. 4

   Step 4

   Optionally add apparent field of view to calculate true FOV

5. 5

   Step 5

   Review all calculated values for optimal viewing setup

• 1

  Maximum useful magnification is typically 2x the aperture in mm (e.g., 200mm scope = 400x max)

• 2

  Lower magnification means brighter images - better for faint objects

• 3

  Exit pupil should be 2-4mm for best deep sky viewing

• 4

  Atmospheric conditions limit useful magnification more than equipment

• 5

  A Barlow lens doubles magnification without buying new eyepieces

• Buying telescopes based on advertised high magnification numbers

• Using maximum magnification in turbulent atmospheric conditions

• Ignoring exit pupil - too small causes dim images, too large wastes light

• Not matching magnification to the object type (planets need high, nebulae need low)