Telescope Comparison
Sky-Watcher Esprit 80ED vs William Optics Zenithstar 73
The specs are close. The experience isn't.
First light
Sky-Watcher · 80mm · £699
The custom-rig optical tube
- 80mm refractor — optical tube only, no mount included
- 480mm focal length at f/6
- Requires a compatible mount before you can observe anything
- Best for: observers who already own a suitable mount or are building a specific imaging rig
- Not a complete purchase — budget at least £100–300 extra for a mount before observing
William Optics · 73mm · £599
The custom-rig optical tube
- 73mm refractor — optical tube only, no mount included
- 430mm focal length at f/5.89
- Requires a compatible mount before you can observe anything
- Best for: observers who already own a suitable mount or are building a specific imaging rig
- Not a complete purchase — budget at least £100–300 extra for a mount before observing
The full picture
The numbers that separate these two scopes — and what they mean at the eyepiece.
Aperture
Sky-Watcher Esprit 80ED gathers 1.2× more light. On bright targets — Moon, Saturn, Jupiter — you won't notice. On fainter targets — dim galaxies, faint globular clusters — the gap is real.
Focal length
Sky-Watcher Esprit 80ED's longer focal length reaches higher magnification with the same eyepiece — better reach for planetary detail. William Optics Zenithstar 73's shorter focal length gives a wider true field — better for large open clusters and extended nebulae.
Focal ratio
Same focal ratio — the same eyepiece gives equivalent magnification and true field in both scopes.
Mount type
Neither scope includes a mount — both require a separate purchase before you can observe.
Weight (OTA)
Similar optical tube weight. Any portability difference between these setups comes from the mount, not the tube itself.
Optical design
Both are refractors — no mirrors to collimate, good contrast, colour-free stars with ED or APO glass. The differences between them are in aperture, focal ratio, and glass quality.
At the eyepiece
| Target | Sky-Watcher Esprit 80ED | William Optics Zenithstar 73 |
|---|---|---|
| Planets | ||
| Moon | Good Clean, chromatic-aberration-free views through the triplet ED optics, but 80mm aperture and short focal length limit high-magnification fine detail. | Moderate 73mm aperture shows good crater and terminator detail, but the short 430mm focal length limits useful magnification before the image softens. |
| Saturn | Moderate Rings visible and well-defined, but 480mm focal length requires very short eyepieces to reach useful magnification — Cassini Division only in excellent seeing. | Challenging Rings visible and Titan identifiable, but 73mm aperture and 430mm focal length can't reveal the Cassini Division or subtle banding. |
| Jupiter | Moderate Main cloud belts visible, but 80mm aperture and 480mm focal length limit the detail and magnification ceiling. | Moderate Main equatorial belts visible; 73mm falls between the Good and Moderate tiers, and the short focal length makes it hard to push magnification for finer detail. |
| Mars | Challenging Small disc visible near opposition, but 80mm aperture is insufficient to reliably show surface features or polar cap. | Challenging Small disc visible near opposition with possible hint of polar cap, but 73mm aperture and short focal length offer very limited surface detail. |
Deep sky | ||
| Orion Nebula (M42) | Excellent 80mm aperture exceeds the threshold and the 480mm f/6 optics frame the full nebula extent with rich wide-field context — superb visually and for imaging. | Good Core nebulosity and Trapezium visible; the wide field at 430mm frames the full nebula complex nicely, but aperture is just under the 80mm Excellent threshold. |
| Andromeda Galaxy (M31) | Excellent 480mm focal length captures the full 3°+ extent of the galaxy including companion galaxies; ideal framing for both visual sweeping and imaging. | Excellent 430mm focal length frames the full galaxy with room to spare; visually the core and inner dust lanes are visible from dark skies. |
| Open clusters | Excellent 480mm focal length provides a wide true field — the Double Cluster, Pleiades, and Beehive are beautifully framed. | Excellent Wide true field at 430mm is ideal for the Double Cluster, Pleiades, and other large clusters — they sit beautifully in the field of view. |
| Globular clusters | Challenging 80mm aperture cannot resolve individual stars — globulars appear as fuzzy, unresolved patches. | Challenging 73mm aperture shows M13 and M22 as fuzzy unresolved glows — no star resolution possible at this aperture. |
| Faint galaxies | Moderate Many galaxies detectable visually as faint smudges; long-exposure imaging through a suitable mount recovers far more, but aperture is the limiting factor. | Challenging 73mm gathers limited light; only the brightest galaxies like M81/M82 show as faint smudges visually. |
| Milky Way / wide field | Excellent 480mm focal length at f/6 delivers sweeping star fields visually and wide rich Milky Way frames for imaging. | Excellent 430mm focal length at f/5.9 delivers sweeping rich star fields — among the best use cases for this scope visually and with a camera. |
Other | ||
| Double stars | Good Clean APO optics and 80mm aperture resolve wide and moderate doubles crisply, though close pairs under 1.5 arcseconds are beyond the Dawes limit. | Moderate 73mm resolves wide doubles like Albireo easily, but the short focal length and modest aperture limit splitting of closer pairs. |
| Astrophotography (deep sky) | Not recommended No mount included — the OTA is designed for deep-sky imaging, but without an equatorial tracking mount it cannot be rated. Paired with an HEQ5 or similar, performance would be Excellent. | Not recommended No mount or tracking included; the OTA is excellent for deep sky imaging but only when paired with an equatorial tracking mount purchased separately. |
| Astrophotography (planetary) | Challenging 80mm aperture and 480mm focal length yield a small planetary image scale; even with a 3× Barlow the effective focal length is modest for planetary work. | Challenging 73mm aperture and 430mm focal length produce a very small planetary image scale — a Barlow helps but aperture is the fundamental limit. |
| Emission nebulae (imaging) | Excellent Fast f/6 focal ratio and wide field are ideal for large emission nebulae like the North America, Heart, and Rosette when paired with a narrowband filter and tracking mount. | Not applicable |
The real tradeoff
Both scopes are capable. The question is which one fits the way you actually observe.
Sky-Watcher Esprit 80ED
- You're buying the triplet APO advantage: corner stars stay tight across full-frame sensors, and chromatic aberration on the Moon becomes a non-issue even at high magnification — this is the optical refinement you're paying for.
- Your imaging sessions reward patience with large targets like M31 and the Heart-Soul pair, where the 480mm focal length and f/6 speed combine to frame entire complex structures in single exposures.
- You'll face the reality that 80mm aperture means longer total integration time on faint galaxies; the cleaner optics help manage noise, but photons are photons — deep integration is non-negotiable for dim targets.
William Optics Zenithstar 73
- You're trading aperture for portability and price: at 73mm and £100 cheaper, this scope weighs less and fits tighter into travel rigs without sacrificing the wide-field imaging character that defines both of these OTAs.
- Your observing sessions feel fastest at the eyepiece on bright targets like M42 and the Pleiades, where the compact focal length and wide true field let you drink in context that a longer scope would slice into pieces.
- You'll discover that the mandatory Flat73A flattener isn't optional — without it, your field edges soften noticeably, turning what looks like a straightforward imaging platform into a two-component system that must be tuned together.
The dark side
Every scope has a personality. Here’s where each one gets difficult.
Sky-Watcher
Sky-Watcher Esprit 80ED
Sold as OTA only — you cannot use this scope until you source an equatorial mount, camera, and accessories, making the true entry cost £2,000+.
The included field flattener requires exact 55mm back-focus spacing; incorrect spacing will introduce field curvature across your images, and discovering this mid-session means troubleshooting before you can observe.
80mm aperture limits both planetary magnification (reaching 200× requires an impractical 2.4mm eyepiece) and deep integration times for faint galaxies, making this a one-dimensional tool for visual work.
William Optics
William Optics Zenithstar 73
Sold as OTA only — no mount, eyepiece, diagonal, or finder included, so you cannot observe until you assemble a complete system, and the total cost climbs well above the £599 OTA price.
The Flat73A field flattener is essentially mandatory for imaging; without it, stars towards the field edges show noticeable coma and curvature, meaning the flattener is a hidden cost and non-negotiable component.
As an ED doublet rather than a triplet, residual chromatic aberration is visible on very bright stars in high-resolution images, and the 2-inch focuser rack-and-pinion can show minor flexure under heavy camera-filter-train loads without careful balancing.
Which is right for you?
Two different buyers. Two different right answers.
The custom-rig optical tube
Sky-Watcher · Sky-Watcher Esprit 80ED
You'll love the Esprit 80ED if you're an intermediate astrophotographer with an existing equatorial mount and camera setup, and you want the cleanest triplet optics to frame enormous emission nebulae and galaxy groups in a single wide-field exposure — you're not a visual observer, and you understand that 80mm aperture means committing to longer integration times.
The custom-rig optical tube
William Optics · William Optics Zenithstar 73
This is your scope if you prioritize portability and budget without sacrificing wide-field imaging capability, or if you're a visual observer who occasionally images bright deep-sky objects like the Orion Nebula and open clusters — you're not pursuing faint galaxies visually, and you accept that the Flat73A flattener is a mandatory add-on that transforms the OTA into a proper imaging platform.
Our verdict
These two are closer than most comparisons on this site. The spec differences are genuine — mount type, focal ratio — but neither is the wrong answer for a typical observer starting out.
If I had to choose between them: the Sky-Watcher Esprit 80ED is the scope most people will be using regularly six months from now. The William Optics Zenithstar 73 rewards you more once you know what you're doing — it's worth revisiting after your first year.
Sky-Watcher Esprit 80ED
View Sky-Watcher Esprit 80ED →William Optics Zenithstar 73
View William Optics Zenithstar 73 →Deep field: Full specifications
Every data point, for those who want to go further.
Full specifications
Fields highlighted in blue or amber indicate the better value for that spec. Data is manufacturer-stated and may vary.
How much can it see?
| Spec | Sky-Watcher Esprit 80ED | William Optics Zenithstar 73 |
|---|---|---|
Apertureⓘ The most important spec — bigger = more light = better views | 80mm | 73mm |
Focal Length Longer = more magnification potential | 480mm | 430mm |
Focal Ratio Lower f-number = wider field of view; higher = more magnification per eyepiece | f/6 | f/5.89 |
Optical Design The type of optics — each design has different strengths | Refractor | Refractor |
Coatings Better coatings = more light transmission through the optics | Fully multi-coated ED triplet with FMC on all air-to-glass surfaces | Fully multi-coated FMC ED doublet on all air-to-glass surfaces |
How do you point it?
| Spec | Sky-Watcher Esprit 80ED | William Optics Zenithstar 73 |
|---|---|---|
Mount Type The mechanical system that holds and moves the telescope | None (OTA only) | None (OTA only) |
GoTo Computer-controlled pointing — finds any of thousands of objects automatically | ||
Tracking Motor keeps objects centred as the Earth rotates — essential for astrophotography |
The focuser
| Spec | Sky-Watcher Esprit 80ED | William Optics Zenithstar 73 |
|---|---|---|
Focuser Size 2" accepts wider eyepieces and gives better low-power views | 2" | 2" / 1.25" |
Focuser Type Rack-and-pinion is standard; Crayford and dual-speed are smoother | Dual-speed Crayford (10:1 reduction, with 1.25" adapter) | Dual-speed Crayford 2" (10:1 reduction fine focus) |
Size & weight
| Spec | Sky-Watcher Esprit 80ED | William Optics Zenithstar 73 |
|---|---|---|
OTA Weightⓘ Optical tube only — useful for comparing mount load capacity | 2.55kg | 1.75kg |
Tube Length | 450mm | 320mm |
Tube Material | Aluminium, white powder coat | Aluminium, anodised blue |
What's in the box?
| Spec | Sky-Watcher Esprit 80ED | William Optics Zenithstar 73 |
|---|---|---|
Diagonal Tilts the eyepiece 90° for comfortable viewing — useful on refractors |
Blue highlight: Sky-Watcher Esprit 80ED advantage · Amber highlight: William Optics Zenithstar 73 advantage · Greyed cells: equal or subjective.