Telescope Comparison
Vixen ED80Sf vs William Optics GT81
The specs are close. The experience isn't.
First light
Vixen · 80mm · £649
The custom-rig optical tube
- 80mm refractor — optical tube only, no mount included
- 600mm focal length at f/7.5
- 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 · 81mm · £699
The custom-rig optical tube
- 81mm refractor — optical tube only, no mount included
- 478mm focal length at f/5.9
- 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
William Optics GT81 gathers 1× 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
Vixen ED80Sf's longer focal length reaches higher magnification with the same eyepiece — better reach for planetary detail. William Optics GT81's shorter focal length gives a wider true field — better for large open clusters and extended nebulae.
Focal ratio
William Optics GT81's faster f/5.9 delivers wider fields with any eyepiece — better for open clusters and large nebulae. Vixen ED80Sf's f/7.5 provides more magnification per eyepiece — better for fine planetary detail.
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 | Vixen ED80Sf | William Optics GT81 |
|---|---|---|
| Planets | ||
| Moon | Excellent 80mm aperture with ED glass delivers sharp, colour-free crater detail; f/7.5 handles high magnification well | Excellent 81mm aperture delivers sharp, high-contrast lunar detail; the triplet design keeps the terminator free of colour fringing, though the short focal length limits magnification without a Barlow |
| Saturn | Good Rings clearly defined, Cassini Division visible in steady seeing; 600mm focal length adequate for useful magnification with a short Barlow | Moderate Rings clearly visible and colour-free, but 81mm aperture and 478mm focal length make the Cassini Division very difficult |
| Jupiter | Good Main equatorial belts and GRS visible; ED glass keeps the limb clean, but 80mm limits fine belt detail | Moderate Main equatorial belts visible in steady seeing; 81mm resolves limited banding detail and the Great Red Spot is marginal |
| Mars | Challenging Small orange disc visible at opposition; polar cap hints possible but aperture too small for surface detail | Challenging Small orange disc visible at opposition; 81mm aperture insufficient to resolve surface features reliably |
Deep sky | ||
| Orion Nebula (M42) | Excellent 80mm aperture and 600mm focal length frame the full nebula with surrounding structure; trapezium resolved | Excellent Bright nebula easily visible; 478mm focal length at f/5.9 frames the full extent with surrounding nebulosity |
| Andromeda Galaxy (M31) | Excellent 600mm focal length captures the full extent of the galaxy; bright core and inner dust lanes visible | Excellent 478mm focal length captures the core and dust lanes in a single wide field; aperture shows the inner halo structure |
| Open clusters | Excellent 600mm focal length gives wide true field — Pleiades, Double Cluster, and M35 all fit beautifully with pinpoint stars | Excellent Wide-field sweet spot — Pleiades, Double Cluster, and M35 are beautifully framed with colour-free stars |
| Globular clusters | Moderate M13 and M3 appear as fuzzy concentrated balls; 80mm cannot resolve individual stars | Challenging 81mm aperture shows globulars like M13 as fuzzy balls with no individual star resolution |
| Faint galaxies | Moderate Brighter Messier galaxies (M81/M82, M51) visible as faint smudges; no structure detail at 80mm | Moderate Core of brighter galaxies like M81/M82 visible under dark skies, but 81mm gathers limited light for faint targets |
| Milky Way / wide field | Good 600mm is slightly long for sweeping Milky Way fields but still delivers rich star clouds with a wide-field eyepiece | Excellent 478mm at f/5.9 is ideal for sweeping rich star fields; low-power eyepieces deliver expansive true fields |
Other | ||
| Double stars | Good Clean ED optics split Albireo easily and handle tighter pairs like Castor; Dawes limit ~1.45 arcsec | Good Clean optics split wider doubles cleanly with no false colour, but 81mm limits resolution on close pairs below about 1.4 arcseconds |
| Astrophotography (deep sky) | Not applicable | Not recommended No mount or tracking included; however, when paired with a suitable equatorial mount this becomes an excellent deep-sky imaging platform at f/5.9 |
| Astrophotography (planetary) | Not applicable | Challenging 81mm aperture and 478mm focal length produce a small planetary image scale; limited even with a Barlow |
| Large emission nebulae (imaging) | Not applicable | Excellent Fast f/5.9 triplet with flat, colour-free field excels on targets like the Veil, North America Nebula, and Heart Nebula when paired with a narrowband or one-shot colour camera on a tracking mount |
The real tradeoff
Both scopes are capable. The question is which one fits the way you actually observe.
Vixen ED80Sf
- You'll spend your visual nights enjoying Saturn's Cassini Division and lunar rilles with the sharpness that 600mm of focal length gives you, accepting that bright stars stay white and the field stays clean across your entire eyepiece.
- Your observing sessions reward patience with planetary targets — Jupiter's belts and the Great Red Spot reveal themselves in steady seeing, but you won't be chasing Mars detail or hunting faint galaxy structure.
- If you add an equatorial mount, you'll have a dedicated deep-sky imaging platform that renders well-corrected star shapes across an APS-C sensor, though you'll need a field flattener to eliminate edge coma.
William Optics GT81
- You'll spend your visual nights sweeping the Milky Way and framing entire nebulae in a single low-power field, accepting that Saturn's Cassini Division and fine lunar detail remain just out of reach because of the short 478mm focal length.
- Your observing sessions reward wide-field targets — the Orion Nebula with surrounding nebulosity, M31's dust lanes, and open clusters resolved into individual stars are all rendered spectacularly in the triplet's colour-free field.
- If you add a tracking mount and camera, you'll have a serious widefield imaging platform where the fast f/5.9 ratio and flat, colour-free field make targets spanning a degree or more your natural specialty.
The dark side
Every scope has a personality. Here’s where each one gets difficult.
Vixen
Vixen ED80Sf
OTA only — you'll need to budget separately for an equatorial mount, diagonal, finder, and eyepieces, making the true entry cost significantly higher than the £649 price tag.
80mm aperture limits deep-sky resolution and planetary detail compared to 100mm+ instruments at similar price; globular clusters remain unresolved and faint galaxies show no internal structure.
The 1.25" focuser limits your eyepiece and accessory choices compared to 2" focuser refractors; at f/7.5, a dedicated field flattener is required for astrophotography to eliminate edge coma and field curvature.
William Optics
William Optics GT81
OTA only — you'll need to budget separately for a mount, diagonal, and eyepieces, making the true system cost well above the £699 price tag.
81mm aperture and 478mm focal length severely limit high-magnification use; pushing magnification requires short-focal-length eyepieces or a Barlow, which compromises eye relief and makes planetary detail chasing frustrating.
Field curvature at the edges of the native focal plane requires a dedicated flattener for serious astrophotography; some production runs lack a built-in focuser lock, risking slip when using heavy imaging trains.
Which is right for you?
Two different buyers. Two different right answers.
The custom-rig optical tube
Vixen · Vixen ED80Sf
You'll love the ED80Sf if you're an intermediate observer who values clean, colour-free lunar and planetary views at moderate magnification, and you're willing to invest in an equatorial mount to unlock its potential as a dedicated deep-sky imaging platform for emission nebulae and large star fields. This scope rewards patience with planetary targets and patience with system-building.
The custom-rig optical tube
William Optics · William Optics GT81
This is perfect for you if you're excited by widefield visual sweeping — framing entire nebulae and star clouds in a single eyepiece field — and you plan to pair it with a tracking mount for serious deep-sky astrophotography of large targets like the Veil Nebula or M31. You're not chasing planetary detail or faint galaxy structure; you're after the spectacular views that only a fast, colour-free widefield refractor can deliver.
Our verdict
Same aperture, same light-gathering, £50 price difference. The extra cost of the William Optics GT81 buys a different mount — not better optics.
For most beginners, the Vixen ED80Sf is the right starting point — the optics are identical and the savings are better spent on a quality eyepiece or a dark-sky trip. The William Optics GT81 makes sense if the mount it comes with is specifically what you want to learn. If I had to choose: the Vixen ED80Sf — same sky, less money.
Vixen ED80Sf
View Vixen ED80Sf →William Optics GT81
View William Optics GT81 →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 | Vixen ED80Sf | William Optics GT81 |
|---|---|---|
Apertureⓘ The most important spec — bigger = more light = better views | 80mm | 81mm |
Focal Length Longer = more magnification potential | 600mm | 478mm |
Focal Ratio Lower f-number = wider field of view; higher = more magnification per eyepiece | f/7.5 | f/5.9 |
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 doublet on all air-to-glass surfaces | Fully multi-coated FMC ED triplet on all air-to-glass surfaces |
How do you point it?
| Spec | Vixen ED80Sf | William Optics GT81 |
|---|---|---|
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 | Vixen ED80Sf | William Optics GT81 |
|---|---|---|
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 (with 1.25" adapter) | Dual-speed Crayford 2" (10:1 reduction fine focus) |
Size & weight
| Spec | Vixen ED80Sf | William Optics GT81 |
|---|---|---|
OTA Weightⓘ Optical tube only — useful for comparing mount load capacity | 1.8kg | 2.5kg |
Tube Length | 528mm | 380mm |
Tube Material | Aluminium | Aluminium, anodised |
What's in the box?
| Spec | Vixen ED80Sf | William Optics GT81 |
|---|---|---|
Diagonal Tilts the eyepiece 90° for comfortable viewing — useful on refractors |
Blue highlight: Vixen ED80Sf advantage · Amber highlight: William Optics GT81 advantage · Greyed cells: equal or subjective.