Celestron Inspire 100AZ vs AstroMaster 70AZ: Which to Buy?
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Planets through a beginner refractor — choosing between the Inspire 100AZ and AstroMaster 70AZ shapes what detail you extract on your first sessions

Telescope Comparison · Celestron Beginner Refractors

Celestron Inspire 100AZ vs AstroMaster 70AZ: Which to Buy?

Two of Celestron's most popular beginner refractors — and they make a genuinely different optical trade-off. The Inspire 100AZ gives you more aperture and a built-in smartphone adapter. The AstroMaster 70AZ gives you cleaner optics with significantly less chromatic aberration. Neither is universally better. Here is exactly which one to choose for your goals.

Inspire 100AZ100mm f/6.6 achromat
AstroMaster 70AZ70mm f/12.9 achromat
Light gatheringInspire gathers 2× more
Optics clarityAstroMaster far less CA
By Telescope Advisor Editorial Team Published: Updated: Editorial Standards

Quick Verdict

Buy the Inspire 100AZ if:

  • ✓ You want to photograph the Moon and planets with your phone — built-in adapter is genuinely better than clip-ons
  • ✓ You want more light-gathering for star clusters, bright galaxies, and nebulae
  • ✓ You plan to observe a variety of targets, not just Moon and planets

Buy the AstroMaster 70AZ if:

  • ✓ Clean, chromatic-aberration-free planetary and lunar views are the priority
  • ✓ You primarily observe the Moon and bright planets at high magnification
  • ✓ A simpler, lighter, more portable setup appeals


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Full Specifications Compared

Celestron Inspire 100AZ refractor with built-in smartphone adapter

Celestron Inspire 100AZ

View on Amazon →
Celestron AstroMaster 70AZ refractor telescope

Celestron AstroMaster 70AZ

View on Amazon →
SpecificationInspire 100AZAstroMaster 70AZWinner
Aperture100mm (4 inches)70mm (2.76 inches)Inspire (2× more light)
Focal length660mm900mmAstroMaster (longer reach)
Focal ratiof/6.6f/12.9AstroMaster (less CA)
Chromatic aberrationModerate at high magVery low (excellent)AstroMaster clearly
Smartphone adapterBuilt into focuserNot includedInspire clearly
Eyepiece format1.25" standard1.25" standardTie — both upgradeable
Limiting magnitude~11.8~11.3Inspire (0.5 mag deeper)
Max useful magnification~200×~140×Inspire

100mm vs 70mm: What the Aperture Difference Actually Delivers

100mm gathers approximately twice the light of 70mm — aperture area scales as the square of the diameter (100² = 10,000 vs 70² = 4,900 square millimetres). In practical terms at the eyepiece, this translates to a difference that is noticeable but not dramatic on the brightest targets, and significant on extended objects.

Where 100mm clearly wins

  • Globular clusters: At 100mm, M13 Hercules begins to resolve individual outer stars at 100–150×. At 70mm it remains a compressed ball of light.
  • Galaxies: Andromeda, Triangulum, and Leo Triplet members are noticeably brighter and more defined in their oval shapes.
  • Nebulae: Orion Nebula nebulosity extends further; the Trapezium is cleanly split; the Ring Nebula (M57) is convincingly annular.
  • Higher magnification ceiling: ~200× potential vs ~140× provides more range on excellent seeing nights.

Where the gap is smaller

  • Moon: Both deliver impressive views. Extra brightness at 100mm is less meaningful when the Moon is already uncomfortably bright without a filter.
  • Saturn rings: Both telescopes show the rings clearly. The AstroMaster's cleaner optics at f/12.9 partially compensates for the aperture difference.
  • Jupiter cloud belts: Both show the equatorial belts; the Inspire shows 3+ more clearly, the AstroMaster delivers a cleaner image edge.
  • Double stars: Both resolve the same moderately tight doubles — aperture advantage is less decisive here.

The aperture advantage is most meaningful for faint extended objects (nebulae, galaxies, globular clusters) and least meaningful for the Moon and bright planets. If 90% of your observing will be the Moon, Jupiter, and Saturn, the AstroMaster's cleaner optics at f/12.9 often matter more than the extra aperture. See what 70mm shows: what a 70mm telescope shows.

Chromatic Aberration: The Most Important Practical Difference

Chromatic aberration — the purple or blue fringing that achromatic refractors produce on bright high-contrast objects — is the most consequential optical difference between these two telescopes, and it comes entirely from the focal ratio difference. The physics: achromatic doublet lenses cannot focus all wavelengths at the same point — red and blue focus at slightly different distances from the lens. Longer focal ratio = less chromatic aberration.

AstroMaster 70AZ at f/12.9 — Excellent CA control

At f/12.9, chromatic aberration is very well controlled for an achromatic doublet. On the Moon's bright limb — where CA is most visible — the fringe is subtle enough that most observers find it non-distracting. Star images appear as tight, clean points. Planetary disk edges are crisp and well-defined. This is genuinely good optics at this price tier. The f/12.9 focal ratio is specifically the reason this telescope is recommended for planetary and lunar work.

Inspire 100AZ at f/6.6 — Moderate CA

At f/6.6, chromatic aberration is more visible — a purple/blue fringe along the Moon's bright limb and around Venus and Jupiter at high magnification. At low power (25mm eyepiece ≈ 26×) the CA is minimal. At the supplied 10mm eyepiece (≈ 66×) it is noticeable, particularly on the Moon's limb and on planetary disk edges. It does not prevent useful observation, but is an objectively inferior optical experience vs f/12.9 on these specific targets.

Bottom line: If your primary interest is planetary observing — especially the Moon at high magnification — the AstroMaster 70AZ's f/12.9 optics consistently produce a more satisfying experience than the Inspire 100AZ, despite the aperture deficit. For deep-sky variety observing, the Inspire's 100mm aperture delivers more overall capability and the CA is a secondary concern.

Smartphone Photography: Inspire Wins Clearly

The Inspire 100AZ's built-in smartphone adapter — integrated directly into the focuser housing rather than clipped onto the eyepiece — provides stable, repeatable positioning relative to the optical axis. The result is better afocal photography and less setup frustration than clip-on alternatives that shift during sessions.

The AstroMaster 70AZ includes no phone adapter. A separate 1.25" clip-on adapter is purchasable from third-party sources, but the experience is noticeably less convenient. For casual Moon and planet photography, the Inspire wins clearly on setup ease.

Photography irony: Phone cameras exaggerate chromatic aberration more than the human eye does — making the Inspire 100AZ's f/6.6 CA more visible in photos than in visual observing. The AstroMaster 70AZ would actually produce cleaner Moon photographs due to its f/12.9 CA control, even though it needs a separate phone adapter. If Moon photo quality matters most, consider this trade-off. Guide: Moon photography guide.

Target-by-Target Comparison

TargetInspire 100AZAstroMaster 70AZEdge
Moon at high magImpressive; moderate CA at limbCrisp, clean edges — minimal CAAstroMaster
Saturn ringsCassini accessible under good seeingRings clear, cleaner imageTie
Jupiter cloud belts3+ belts, 4 moons visible2 belts, 4 moons — cleaner edgesInspire (aperture)
Venus phaseCA visible on bright diskClean phase, minimal CAAstroMaster
Globular clustersOuter stars begin to resolve at 100mmCompressed ball — no resolutionInspire clearly
Andromeda GalaxyNoticeably brighter, more extentFaint oval — identifiableInspire
Orion Nebula (M42)Good nebulosity; Trapezium cleanly splitFainter; Trapezium splitInspire (aperture)
Moon photographyBuilt-in adapter — convenient, more CA in photosNo adapter; but cleaner imagesDepends on priority

Mount, Tripod, and Accessories

Both telescopes use a basic manual alt-azimuth mount — no slow-motion controls, no motorised tracking. Planets and the Moon drift across the field as Earth rotates, requiring periodic nudges. Both are adequate for casual beginner sessions. Neither will win awards for stability at very high magnification, which is typical at this price tier.

Critically, both use the standard 1.25" eyepiece barrel — the universal format compatible with the full aftermarket. Any quality eyepiece, Barlow lens, colour filter, or moon filter purchased for either telescope will work in the other, and will continue to work in any future telescope with a 1.25" focuser. There is no proprietary ecosystem lock-in with either instrument.

First accessories worth adding to either telescope: a variable polarizing moon filter (reduces full Moon glare dramatically — see our moon filter guide) and an upgraded eyepiece set (Plössl quality improves significantly on the included eyepieces — see best eyepiece sets 2026).

Upgrade Path and Accessories Context

Both telescopes are starting points, not endpoints. Understanding where each leads helps you choose the right one for your likely trajectory as an observer.

For Inspire 100AZ owners — the eyepiece upgrade matters most

The Inspire 100AZ's 100mm aperture is genuinely capable, but the included eyepieces limit what it shows. Upgrading to quality Plössl eyepieces in 9mm, 15mm, and 32mm focal lengths will make a noticeable difference on planets, globular clusters, and deep-sky objects — more than any other single accessory change. Colour filters also work well on 100mm instruments: a #8 yellow improves Jupiter belt contrast, a #82A light blue enhances Saturn ring/disk definition. See: planetary colour filter guide.

For AstroMaster 70AZ owners — aperture is the limiting factor

The AstroMaster 70AZ's optics are clean enough that eyepiece upgrades provide moderate improvement. The fundamental limitation is aperture — 70mm restricts deep-sky performance regardless of eyepiece quality. After 6–12 months of satisfying lunar and planetary work, most AstroMaster owners who want to go deeper will look toward 100–130mm instruments. The natural upgrade path is to a 130mm Newtonian (Sky-Watcher Heritage 130P tabletop Dob) or the Inspire 100AZ itself, where the aperture jump is immediately obvious.

Third option that outperforms both: Sky-Watcher Heritage 130P

If neither telescope feels like the right trade-off, the Sky-Watcher Heritage 130P tabletop Dobsonian is worth strong consideration. At 130mm with a parabolic mirror, it has zero chromatic aberration (reflectors don't suffer from CA), gathers 2.6× more light than the Inspire 100AZ's 100mm, and sits on a smooth tabletop Dobsonian base that is inherently more stable than a tripod-mounted alt-az at high magnification. The only trade-off: no tripod (it sits on a table or flat surface), and it's a reflector that needs periodic collimation. For the majority of beginners, it is the better first purchase. Full review: Heritage 130P review.

View Heritage 130P on Amazon →

Final Verdict by Use Case

General variety observers → Inspire 100AZ

For observers who want to explore the full sky — Moon, planets, star clusters, globulars, bright galaxies, and double stars — the Inspire 100AZ's 100mm aperture and built-in smartphone adapter deliver more overall capability. The chromatic aberration is a real limitation at high magnification on bright targets, but the depth of experience across object types compensates. Full review: Inspire 100AZ full review.

View Inspire 100AZ on Amazon →

Dedicated planetary and lunar observers → AstroMaster 70AZ

For observers who will spend the majority of sessions on the Moon, Saturn, Jupiter, Venus, and double stars, the AstroMaster 70AZ's f/12.9 optics deliver consistently more satisfying high-magnification views. The clean, sharp planetary disk edges and minimal chromatic aberration make prolonged lunar work comfortable and rewarding, even with the aperture deficit.

View AstroMaster 70AZ on Amazon →

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What First-Time Buyers Should Actually Expect

Reading specifications and comparison tables helps frame the choice, but the actual observing experience reveals practical differences that specs alone cannot capture. Here is what genuinely matters for new observers with either instrument.

With the Inspire 100AZ, the first experience most observers notice is how much brighter and more detailed the Moon appears compared to any telescope they may have encountered before. The 100mm aperture delivers genuinely impressive views immediately: craters, mountain chains, and the dramatic terminator shadow line are all immediately striking. The chromatic aberration, while present, is not the dominant impression on that first night. What dominates is the sense that this is a real instrument showing real astronomical detail. Star clusters like the Pleiades fill the wide-field eyepiece; Jupiter shows its equatorial cloud bands; Saturn's rings are unmistakably oval. As you move to higher magnification over subsequent sessions, the chromatic fringing on the Moon's limb becomes more noticeable — particularly at the telescope's maximum useful range of 150–200×. Most observers at this stage either accept it as a characteristic of the instrument or begin thinking about the upgrade to a parabolic reflector that eliminates it entirely.

With the AstroMaster 70AZ, images are slightly smaller and dimmer — 70mm gathers half the light of 100mm — but noticeably cleaner on the Moon and bright planets. Experienced observers consistently comment on the crispness of crater edges and the clean definition of Saturn's ring boundaries. The telescope performs best at its moderate magnification range of 50–120×, where the f/12.9 optics show essentially no chromatic aberration. Both telescopes will share one frustration for beginners: objects move out of the field of view as Earth rotates, requiring periodic manual nudges. This is how manual alt-azimuth mounts work. The habit of tracking resolves quickly — most beginners find it natural within 2–3 sessions. Both will also benefit from eyepiece upgrades: the supplied eyepieces are functional but quality Plössl replacements improve the experience noticeably. See our eyepiece sets guide. A variable polarising moon filter is also worth adding for both telescopes — when the Moon is near full, both 100mm and 70mm apertures deliver enough light to make comfortable prolonged observing difficult without attenuation. A variable filter screwing onto any 1.25" eyepiece solves this immediately and costs less than a quality eyepiece. See: best moon filter for telescopes.

FAQ

Is the Celestron Inspire 100AZ worth more than the AstroMaster 70AZ?

For most observers — yes. The 100mm aperture gathers twice the light of 70mm, and the built-in smartphone adapter is a genuine convenience upgrade. The chromatic aberration at f/6.6 is the Inspire's main limitation but is manageable at moderate magnifications where most beginners spend their observing time. If you plan to observe a variety of objects beyond just the Moon and planets, the Inspire 100AZ covers more ground.

Which shows Saturn's rings better?

Both show Saturn's rings clearly. The Inspire 100AZ gives slightly more resolution and brightness at 100mm; the Cassini Division is accessible under good seeing at 130×+. The AstroMaster 70AZ delivers a slightly cleaner image due to f/12.9 optics. In practice, both produce rewarding Saturn views — the bigger variable is atmospheric seeing and eyepiece quality. See: best eyepiece for Saturn and the upcoming October 4 Saturn opposition guide.

Does the Inspire 100AZ include a smartphone adapter?

Yes. The smartphone adapter is integrated directly into the Inspire 100AZ focuser housing as a standard feature — not an optional accessory. It accommodates most current smartphones and provides stable, repeatable positioning for afocal Moon and planet photography. This is the defining hardware innovation of the Inspire series.

Are the eyepieces interchangeable between both telescopes?

Yes. Both use the standard 1.25" eyepiece barrel format — compatible with the full aftermarket. Any eyepiece, Barlow, colour filter, or moon filter purchased for one works in the other and in any future 1.25" telescope. See: best eyepiece sets 2026.

What does f/6.6 vs f/12.9 mean for a refractor?

Focal ratio (f/number) in a refractor determines chromatic aberration — how much false colour fringing an achromatic doublet produces on bright, high-contrast targets. Lower f/number (faster) = more CA; higher f/number (slower) = less CA. The AstroMaster 70AZ at f/12.9 produces very little visible fringing — comfortable for extended lunar and planetary observing. The Inspire 100AZ at f/6.6 produces more fringing, visible as purple/blue on the Moon's limb and Venus at high magnification.



Related Guides

Best Telescopes for Beginners 2026

All beginner options ranked — refractors, Dobsonians, app-guided.

Sky-Watcher Heritage 130P Review

The budget telescope that outperforms both options on most targets.

Best Eyepiece for Saturn's Rings

Which focal length maximises ring detail through either telescope.

Best Telescope Eyepiece Sets 2026

Both use 1.25" eyepieces — upgrade kits that work with either scope.

Best Moon Filter 2026

Variable polarizing filter — essential for full Moon observing in both telescopes.

How to Photograph the Moon

Step-by-step smartphone Moon photography guide for both scopes.