Choosing and Using Telescope Eyepieces: Getting the Most from Every Observation

The eyepiece is where your telescope meets your eye. Choosing the right one transforms your observing experience from frustrating to breathtaking. Photo: NASA/Goddard Space Flight Center (Public Domain)

The Most Important Accessory You Own

You can spend thousands of dollars on a telescope with exquisite optics, but if you are viewing through a cheap, poorly designed eyepiece, you are throwing much of that investment away. The eyepiece is the final optical element between the telescope and your eye. It determines the magnification, the field of view, the sharpness at the edges, the comfort of viewing, and ultimately how much you enjoy your time at the telescope. A good eyepiece can make a modest telescope perform beautifully. A bad one can make an excellent telescope look mediocre.

The good news is that the eyepiece market has exploded with excellent options at every price point. Whether you are building your first set of eyepieces on a tight budget or assembling a premium collection, understanding how eyepieces work. If you are also interested in astrophotography, and what to look for will help you make choices you will be happy with for years.

How Eyepieces Work

An eyepiece is a small lens assembly that magnifies the focused image produced by your telescope’s primary optic (mirror or lens). The relationship is straightforward:

Magnification = Telescope focal length / Eyepiece focal length

For example, a telescope with a 1,200mm focal length paired with a 25mm eyepiece produces 48x magnification (1200/25 = 48). The same telescope with a 10mm eyepiece produces 120x (1200/10 = 120). Shorter focal length eyepieces produce higher magnification.

This means you change magnification by swapping eyepieces. A set of three to five well-chosen eyepieces covers the full range of useful magnifications for your telescope.

Key Eyepiece Specifications

Focal Length

Determines magnification as described above. Eyepieces typically range from 3mm (very high power) to 40mm (very low power). Most observers use eyepieces in the 6mm to 32mm range most frequently.

Apparent Field of View (AFOV)

This is how wide the view appears when you look through the eyepiece, measured in degrees. A wider AFOV gives a more immersive, spacious view. Eyepiece designs range from about 40 degrees (narrow) to over 100 degrees (ultra-wide).

• 40-50 degrees: Traditional designs (Kellner, orthoscopic). Feel like looking through a tunnel.
• 50-55 degrees: Plossl eyepieces. Adequate but still somewhat narrow.
• 60-68 degrees: Wide-field designs. A significant improvement in viewing comfort and context.
• 82 degrees: The “sweet spot” for many observers. Immersive views that feel natural.
• 100+ degrees: Ultra-wide. The view is so wide that you can see the full field without moving your eye. Spectacular but expensive.

The true field of view (how much sky you actually see) is calculated as: True FOV = AFOV / Magnification. A 25mm eyepiece with 68-degree AFOV on a 1200mm telescope gives 68/48 = 1.4 degrees of true field, roughly three full Moon diameters.

Eye Relief

The distance from the eyepiece lens to where your eye must be positioned to see the full field. This is critically important for eyeglass wearers. Short eye relief (under 10mm) requires you to press your eye very close to the lens, which is uncomfortable or impossible with glasses. Eye relief of 15mm or more is recommended for comfortable viewing with eyeglasses.

Exit Pupil

The diameter of the beam of light leaving the eyepiece, calculated as: Exit pupil = Telescope aperture (mm) / Magnification. For the view to be as bright as possible, the exit pupil should not exceed the diameter of your eye’s pupil (about 5-7mm for dark-adapted eyes, less for older observers). An exit pupil larger than your eye’s pupil wastes light. An exit pupil smaller than about 1mm makes the view uncomfortably dim and magnifies every atmospheric flaw.

Eyepiece Designs: What to Buy

Plossl (50-52 degrees AFOV)

The Plossl is the budget workhorse of amateur astronomy. A four-element design that produces sharp, well-corrected images across a 50-52 degree field. Plossls are available from many manufacturers at very affordable prices ($20-$50 per eyepiece). They are an excellent starting point for building an eyepiece collection.

The main limitation of Plossls is narrow apparent field of view and short eye relief at short focal lengths. A 10mm Plossl has only about 7mm of eye relief, which is uncomfortably tight. Below 10mm focal length, Plossls become impractical for most observers.

Orthoscopic (40-45 degrees AFOV)

The classic orthoscopic design uses four elements and is prized for planetary observation. It delivers very sharp, high-contrast views with minimal scattered light, making it ideal for observing fine detail on Jupiter, Saturn, Mars, and the Moon. See also our guide to solar observing for daytime eyepiece use. The narrow field of view is less important for planetary work since planets are small objects that do not need wide fields. Quality orthoscopics from manufacturers like Baader and University Optics run $80-$150.

Wide-Angle Designs (60-68 degrees AFOV)

These offer a significant step up from Plossls in viewing comfort and immersion. Popular options include:

• Explore Scientific 68-degree series: $80-$120 each. Excellent value with sharp views, generous eye relief, and a wide enough field to feel spacious. Many observers consider these the sweet spot of price-to-performance.
• Baader Morpheus (76-degree AFOV): $200-$250 each. Outstanding optical quality, comfortable eye relief, and beautiful build quality. Many experienced observers consider these the best value in premium eyepieces.
• Meade Series 5000 HD-60 (60-degree AFOV): $70-$100 when available. Compact, lightweight, and optically solid.

Ultra-Wide Designs (82-100+ degrees AFOV)

The premium tier of eyepieces. These deliver immersive, “spacewalk” views that transform observing from peering through a window into floating in space.

• Explore Scientific 82-degree series: $150-$200 each. The most affordable 82-degree eyepieces available. Large and heavy, but optically excellent.
• Tele Vue Nagler (82 degrees): $300-$500 each. The original ultra-wide eyepiece, invented by Al Nagler in 1981. Set the standard that everyone else followed. Still outstanding, but premium priced.
• Tele Vue Ethos (100 degrees): $500-$850 each. The ultimate visual eyepiece. The 100-degree field is so wide it defies description. Astronomically expensive, but those who own them rarely regret it.
• APM HDC XWA (100 degrees): $300-$400 each. A more affordable alternative to the Ethos with very good optical quality.

Barlow Lenses: Doubling Your Collection

A Barlow lens is a negative lens (learn more about Barlow lens basics) that increases the effective focal length of your telescope, doubling (2x Barlow) or tripling (3x Barlow) the magnification of any eyepiece you use with it. A 25mm eyepiece becomes effectively a 12.5mm through a 2x Barlow. This means a set of three eyepieces plus a Barlow effectively gives you six magnification options.

Good Barlows from brands like Tele Vue, Explore Scientific, and GSO cost $50-$150 and do not noticeably degrade image quality. A quality 2x Barlow is one of the best investments in an eyepiece collection.

Barrel Sizes: 1.25-inch vs 2-inch

Eyepieces come in two standard barrel diameters:

1.25-inch: The standard for most eyepieces. All telescopes accept 1.25-inch eyepieces. Suitable for focal lengths from about 4mm to 32mm.

2-inch: Used for low-power, wide-field eyepieces (typically 30mm and above). The wider barrel allows a larger field stop, delivering wider true fields of view than a 1.25-inch eyepiece of the same focal length. Many premium eyepieces in the 14mm-30mm range are available in 2-inch format for wider fields. Your telescope needs a 2-inch focuser or adapter to use these.

Filters: Enhancing Your View

Eyepiece filters screw into the barrel threads and can dramatically improve certain observations:

• Moon filter (neutral density): Reduces the Moon’s glare to a comfortable brightness. $10-$20. Essential for lunar observing at high magnification.
• Light pollution filter: Blocks the wavelengths of common artificial lighting (sodium and mercury vapor) while passing natural light from celestial objects. $30-$80. Moderately effective from light-polluted sites.
• OIII filter: A narrowband filter that passes only the doubly-ionized oxygen emission line at 496/501nm. Dramatically improves the visibility of planetary nebulae and certain emission nebulae (Veil Nebula, Crab Nebula). $80-$150. One of the most useful visual filters.
• UHC (Ultra High Contrast) filter: Passes both OIII and hydrogen-beta emission lines. Slightly wider passband than OIII, effective on a broader range of emission nebulae. $60-$120.
• Planetary color filters: Colored glass filters that enhance specific features on planets (red filter for Mars surface detail, blue filter for Jupiter’s cloud detail). $10-$15 each.

Building an Eyepiece Collection on a Budget

You do not need to buy everything at once. Here is a practical strategy for building a collection over time:

Start with three eyepieces:

• A low-power eyepiece (25-32mm) for finding objects and viewing wide star fields and Messier objects
• A medium-power eyepiece (12-15mm) for general observing
• A high-power eyepiece (6-8mm) for planets, double stars, and lunar detail

Add a 2x Barlow to double your effective magnification options.

Then upgrade individual eyepieces as budget allows, starting with the focal lengths you use most. Most observers find they use one or two eyepieces far more than the others. Invest in quality where you spend the most time.

A starting set of three Plossl eyepieces plus a Barlow can be assembled for under $100. Upgrading to Explore Scientific 68-degree or 82-degree eyepieces over time takes that same telescope and makes it feel like a completely different instrument. The views are wider, more comfortable, and more immersive. It is one of the most satisfying upgrades you can make in visual astronomy.

Your telescope gathers the light. Your eyepiece delivers it to your eye. Make sure that delivery system is worthy of what your telescope is collecting. Once you have your eyepieces sorted, check out our guide to observing double stars — they’re perfect subjects for testing your eyepiece resolution.