Which eyepiece should you choose for your telescope?
The two eyepieces that come with an entry-level telescope are enough to get started — but they're often exactly what limits what you can actually see through the instrument.
See the shop ↓| 25 mm Wide-Field Eyepiece | 2x Barlow Lens | Neutral Density Moon Filter | |
|---|---|---|---|
| Price | Around €37 | Around €37 | Around €18 |
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| Who it's for | Beginner | Beginner Advanced | Beginner Kids |
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What an eyepiece actually changes
A telescope's magnification isn't fixed: it depends on the eyepiece being used, following a simple formula — the telescope's focal length divided by the eyepiece's focal length. A telescope with a 900 mm focal length fitted with a 25 mm eyepiece magnifies 36 times; the same telescope with a 6 mm eyepiece magnifies 150 times. That's why a single optical tube can be used both to sweep across a wide field of stars and to zoom in on Jupiter's cloud bands — all it takes is swapping the eyepiece.
The eyepieces that come standard with an entry-level telescope are rarely bad, but there are usually only one or two of them, and their optical quality is modest — narrow field of view, limited visual comfort. Upgrading to one or two better-quality eyepieces, chosen to complement what's already included, often changes the observing experience more than a more expensive telescope would.
Field of view, the forgotten factor behind magnification
Two eyepieces can offer exactly the same magnification and still deliver a very different experience, because of their apparent field of view — the angle the image covers inside the eyepiece, independent of the telescope. A budget eyepiece often offers a 40-50° apparent field, while a more refined model can reach 60-70° or beyond. The higher that number, the more the image feels like an open window onto the sky rather than looking through a narrow tube.
A wide field also makes finding objects far easier: spotting an object in a comfortable field of view, then gradually increasing magnification by swapping eyepieces, is much less frustrating than hunting blindly with a tiny field from the start.
The Barlow lens: doubling your eyepiece collection without overspending
A Barlow lens sits between the focuser and the eyepiece itself, and multiplies the resulting magnification — typically by two. In practice, a 2x Barlow paired with a 25 mm eyepiece and a 10 mm eyepiece gives you access to four different magnifications (25 mm, an effective 12.5 mm, 10 mm, and an effective 5 mm) for the price of a single extra accessory.
It's often the best-value purchase after the eyepieces themselves: rather than buying a third or fourth short-focal-length eyepiece (expensive, and with diminishing returns), a decent-quality Barlow instantly extends your entire existing collection.
Filters: when they're actually worth it
A neutral-density Moon filter reduces the glare of a full Moon viewed through a telescope with decent aperture — without one, the image can be so bright it becomes uncomfortable to look at, and you actually see less crater detail as a result. It's an inexpensive accessory with an immediately noticeable effect, unlike some colored filters whose benefit is more subtle and depends heavily on observing conditions.
Colored filters (yellow, blue, red) can slightly boost the contrast of certain details on the giant planets, but their effect stays fairly subtle: it's not the first accessory to buy, more something to add once you're already observing regularly.
Classic mistakes to avoid
The most common one: stockpiling very-short-focal-length eyepieces on the assumption that "more magnification is always better." Every telescope has a maximum useful magnification, roughly twice its aperture in millimeters — beyond that, the image turns dark and blurry regardless of eyepiece quality, because atmospheric turbulence and the amount of light gathered become the limiting factor, not the optics.
The other classic pitfall involves eye relief: eyeglass wearers need generous eye relief (around 15-20 mm) to see the full field without pressing their eye right up against the lens — a detail rarely highlighted on the packaging, but one that makes a real difference in everyday use.
Examples of suitable accessories
The models below illustrate the categories described above — a wide-field eyepiece for finding objects, a Barlow lens to multiply your available magnifications, and a Moon filter for immediate comfort. Always check compatibility with your telescope's focuser diameter (1.25" in the vast majority of cases for a beginner instrument).
Screws into the telescope to widen the field of view, making it easy to locate an object before zooming in further.
- Wide field of view, makes locating objects much easier
- Compatible with almost all 1.25" telescopes
- Modest magnification, doesn't replace a short-focal-length eyepiece
Fits between the eyepiece and the telescope to instantly double the magnification of any eyepiece you already own.
- Instantly doubles the number of magnifications available
- Cheaper than an equivalent-quality extra eyepiece
- Adds nothing if your current eyepieces are already low quality
Screws onto the eyepiece to cut the glare of the full Moon for more comfortable viewing.
- Immediate visual comfort on the full Moon, noticeable from first use
- Very affordable
- Mainly useful around full Moon, less noticeable at first/last quarter
Frequently asked questions
Do I need to replace all the eyepieces that came with my telescope?
Not necessarily. Keep the one you use most often for finding objects (usually the longest focal length), and add a wide-field eyepiece or a Barlow rather than replacing everything at once.
Which focuser diameter should I get, 1.25" or 2"?
1.25" remains the standard on nearly all beginner-oriented telescopes, and the vast majority of affordable eyepieces are made for this diameter. The 2" format mainly concerns larger instruments and very-wide-field eyepieces, which cost more.
Is a 2x Barlow the same as an eyepiece with half the focal length?
Optically, the final magnification is identical, but a Barlow generally costs less than an additional eyepiece of comparable quality, and it multiplies every eyepiece you already own rather than adding just one.