SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/astro-eyepiece-magnification

With the main optic fixed, what can you swap to change a telescope's magnification?

The eyepiece; swap eyepieces to change magnification.

Start playing free

  1. The eyepiece ✔
  2. The aperture stop
  3. The mirror coating

Why: The main lens or mirror forms an image. The eyepiece magnifies it, and changing eyepieces changes the power. Useful magnification is still limited by aperture and atmospheric turbulence.

Huh, didn't know that: Too much magnification enlarges atmospheric shimmer as well as the target.

The dad joke
My telescope salesman promised 500x power. I saw right through him.
Like this card?
Play the game

References

Answer: The eyepiece. The main lens or mirror forms an image. The eyepiece magnifies it, and changing eyepieces changes the power. Useful magnification is still limited by aperture and atmospheric turbulence.

  1. OpenStax Astronomy 2e, 6.1 Telescopes openstax.org/books/astronomy-2e/pages/6-1-telescopes
    Using different eyepieces, we can change the magnification (or size) of the image and also redirect the light to a more accessible location.
    Checked 2026-10-10.

Think this answer is wrong? Tap "Challenge this answer" on the card in the game and tell us why.

Test yourself in the game

Astronomy & SpaceWhat happens when a foreground star microlenses a background star?Astronomy & SpaceWhich kind of light has the shortest wavelength, under 0.01 nanometer?Astronomy & SpaceRoughly what wavelength range is visible light?

That's stuff everyone should know.