How do I choose the right eyepiece magnification?
The basic formula
Magnification equals the telescope's focal length divided by the eyepiece's focal length. A longer eyepiece gives lower power and a wider field of view. A shorter eyepiece gives higher power but a smaller view that can look dimmer.
The most useful magnification depends on your telescope's opening and the sky conditions. Pushing magnification too high usually makes images blurry rather than clearer. A set of two or three eyepieces covers most beginner needs.
- Divide telescope focal length by eyepiece focal length
- Longer eyepieces give lower power
- Shorter eyepieces give higher power
- Stay within the useful range for your telescope
Match the power to the target
Use low power for star clusters, large nebulae, and finding objects, since the wider field is easier to navigate. Use medium power for the Moon and many planets. Save high power for small, bright targets when the air is steady.
Steady air is the biggest limit on high power, so a calm night often works better than a higher number. Try a few eyepieces on the same target and compare them. Pick the one that gives the clearest view, not the highest number.
- Low power for wide views
- Medium power for the Moon and planets
- High power only on steady nights
Common mistakes
- Assuming more magnification always means a better view.
- Buying many eyepieces before you learn which powers you use most.
