How to choose telescope eyepieces
Updated June 2026Independently researchedNo paid placement.
The best telescope eyepiece for you depends on your telescope’s focal ratio, your observing targets, and your budget. Focus on matching focal length to magnification, choosing a comfortable eye relief, and considering the eyepiece’s apparent field of view. Don’t overspend on ultra-wide eyepieces for a slow telescope; a good Plössl or wide-angle design offers great value.
What do the numbers on an eyepiece mean?
Eyepieces are labeled with two key numbers: focal length (in mm) and barrel diameter (usually 1.25” or 2”). The focal length determines magnification: smaller numbers give higher magnification. For example, a 10 mm eyepiece provides more zoom than a 25 mm eyepiece. The barrel diameter must match your telescope’s focuser or diagonal. A third number you might see is the apparent field of view (AFOV), measured in degrees. A standard Plössl might have 50°, while wide-angle designs like Tele Vue’s Ethos can reach 100°. A wider AFOV lets you see more of the sky at once, but often comes with a higher price.
How to choose the right focal length for your telescope
Magnification is calculated by dividing your telescope’s focal length (in mm) by the eyepiece’s focal length. So a 1000 mm telescope with a 25 mm eyepiece gives 40x magnification. A good rule of thumb is to aim for magnifications between 50x and 150x for most objects, with 200x+ for planets on steady nights. Start with a medium-power eyepiece (around 20-25 mm) for wide views of star clusters and galaxies, then add a high-power eyepiece (5-10 mm) for planets and the moon. Many beginners buy too many mid-range eyepieces; it’s better to get two quality eyepieces that cover low and high power.
Eye relief: why it matters and what to look for
Eye relief is the distance your eye must be from the eyepiece lens to see the full field. For observers who wear glasses, long eye relief (15-20 mm or more) is essential to see the entire field without squinting. Many modern eyepieces, like those from Explore Scientific or Celestron’s Ultima series, offer generous eye relief. Without glasses, you might not notice it, but short eye relief (5-8 mm) on very high-power eyepieces can be uncomfortable, especially for planetary viewing. If you share your telescope with family members who wear glasses, choose eyepieces with at least 15 mm of eye relief.
Budget-friendly eyepieces vs. premium: where to spend
The good news is that eyepiece quality has increased dramatically at lower price points. Budget-friendly options from brands like SVBONY or Celestron’s Plössl line provide sharp views that were considered good just a decade ago. For a very modest investment, you can equip a new telescope with a solid set. Where you see the difference is in edge sharpness, light throughput, and build quality. Premium eyepieces from Tele Vue, Pentax, or Nikon often have wider fields and better contrast, especially in fast telescopes (f/5 or faster). If your telescope is f/8 or slower, a well-reviewed budget Plössl will perform nearly as well as a premium one. Invest in one or two high-quality eyepieces that get the most use.
Understanding barrel sizes: 1.25" vs 2"
Most telescopes come with a 1.25” focuser, which limits the maximum apparent field at low power. A 2” focuser allows larger field stops, enabling wider true fields of view. If your telescope has a 2” focuser, using a 2” eyepiece with a long focal length (like a 30-40 mm wide-angle) can provide stunning panoramic views of the Milky Way or large nebulas. However, 2” eyepieces are heavier and more expensive. Many observers start with 1.25” eyepieces and only add a 2” for wide-field work. Check your telescope’s specifications to see what it accepts; some reflectors have a 2” focuser standard, while small refractors often only take 1.25”.
Frequently asked questions
Can I use any eyepiece with my telescope?
Not exactly. The eyepiece must have the correct barrel diameter (1.25” or 2”) for your focuser, and its focal length must give a magnification that’s within your telescope’s useful range. Also, avoid eyepieces that are too heavy for your focuser’s drawtube.
What is a Barlow lens and should I buy one?
A Barlow lens doubles or triples the magnification of any eyepiece you use with it. It can be a cost-effective way to double your eyepiece collection, one 20 mm eyepiece becomes both 20 mm and 10 mm with a 2x Barlow. Quality Barlows are worth the investment, but cheap ones can degrade image quality.
What does “Plössl” mean?
Plössl is a classic eyepiece design (invented by Ignaz Plössl) with a simple 4-element optical arrangement. It offers a moderate 50–52° apparent field, good sharpness, and very fair prices. Plössls are a solid choice for beginners and experts alike, especially in longer-focal-ratio telescopes.
Are cheap eyepieces okay for a beginner?
Cheap eyepieces (very low price) often have narrow fields, poor coatings, and discomfort. However, many budget-friendly eyepieces from brands like SVBONY, Orion, or Celestron’s lower line offer surprisingly good performance for the money. Read owner reviews and avoid unbranded eyepieces from auction sites.
How many eyepieces do I really need to start?
Three is a good starting set: a low-power (20–30 mm) for wide views, a medium-power (10–15 mm) for general observing, and a high-power (5–8 mm) for planets and lunar detail. Add a Barlow lens to double your options. Resist buying more until you know what you want to observe more.
What is the difference between 1.25" and 2" eyepieces?
The 2” barrel allows a larger field stop, giving a wider true field of view at low magnifications. It’s essential for wide-field deep-sky observing with a 2” focuser. For mid- to high-power, 1.25” eyepieces work perfectly well and are lighter and cheaper.