01
Low power
Wide fields, large nebulae, open clusters, star hopping, and finding objects.
Astronomy Tools · Gear Lab
Eyepiece Planner
Compare several eyepiece focal lengths on the same telescope before buying. See magnification, exit pupil, estimated true field of view, and where each eyepiece sits in the low-to-high power range.
Your telescope
Enter the optical basics once.
Quick telescope presets
Rule-of-thumb range
29× – 406×
Roughly a 7 mm exit pupil at the low end and 2× aperture in millimeters at the high end. Real seeing and optical quality still matter.
Your eyepiece set
Compare up to six eyepieces.
Eyepiece 1
Eyepiece 2
Eyepiece 3
Eyepiece 4
Eyepiece 5
Eyepiece 6
| Eyepiece | Magnification | Exit pupil | True field | Power band | Typical use |
|---|
How to build a useful set
You do not need every focal length.
A practical eyepiece set usually works better when each step produces a meaningful change in magnification or field. Buying 20 mm, 18 mm, and 16 mm eyepieces may create more overlap than value on the same telescope.
02
Medium power
A versatile middle range for many galaxies, nebulae, clusters, and lunar observing.
03
High power
Planets, lunar detail, double stars, and small targets when seeing supports it.
Before buying
Focal length is only part of the eyepiece.
Apparent field, eye relief, edge correction, weight, barrel size, glasses compatibility, distortion, scatter, and how well the eyepiece behaves at your telescope's focal ratio can all matter.
Gear Lab principle
Use the optical math first. Shop second.
Future StarStation eyepiece reviews can layer hands-on comfort, optical behavior, build quality, price, and competing models on top of the same objective numbers shown here.