Three that give genuinely different magnifications in your own telescope, and a Barlow if the gaps are wide. What matters is the spread of magnifications rather than the count, and most starter sets contain duplicates.
The question is asked as a count and answered as a spread, which is why so many eyepiece cases contain more glass than magnifications.
Work in magnifications, not focal lengths
Divide your telescope focal length by each eyepiece focal length and write the answers down. Two eyepieces whose answers are close together are one eyepiece and a duplicate, however different the numbers on their barrels look.
What the three should do
The low power finds things and frames large objects; it is the eyepiece used to point the telescope. The medium power is where most observing happens. The high power comes out for the Moon, for planets and for splitting close doubles, and it is used on fewer nights than anyone expects.
Where a Barlow fits
Between the focuser and the eyepiece, multiplying the effective focal length. It fills gaps cheaply — but check the resulting figures against what you already have, because a 2x Barlow with eyepieces an octave apart reproduces one of them exactly.
What decides quality rather than count
Eye relief and edge performance. A comfortable eyepiece gets used; one that presses your eye against the glass does not, whatever its specification says.
The questions that keep arriving
What magnifications should the three give?
A low power for finding and for large objects, a medium one for most of what you will look at, and a high one for the Moon, planets and double stars. The exact figures follow from your telescope focal length.
Is a Barlow better than buying short eyepieces?
Often, for two reasons: it doubles the number of available magnifications, and it preserves the eye relief that a very short eyepiece of simple design gives up. A poor Barlow, however, degrades every eyepiece used behind it.
Last reviewed 17 September 2026