Telescope Comparison
Vixen ED80Sf vs Vixen SD81S
The price gap is real. The question is whether the extra capability is worth it at your stage.
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
Vixen · 81mm · £1,199
The custom-rig optical tube
- 81mm refractor — optical tube only, no mount included
- 625mm focal length at f/7.72
- 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
Vixen SD81S 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 SD81S's longer focal length reaches higher magnification with the same eyepiece — better reach for planetary detail. Vixen ED80Sf's shorter focal length gives a wider true field — better for large open clusters and extended nebulae.
Focal ratio
Vixen ED80Sf's faster f/7.5 delivers wider fields with any eyepiece — better for open clusters and large nebulae. Vixen SD81S's f/7.72 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 | Vixen SD81S |
|---|---|---|
| Planets | ||
| Moon | Excellent 80mm aperture with ED glass delivers sharp, colour-free crater detail; f/7.5 handles high magnification well | Excellent 81mm aperture with superb colour correction delivers crisp, fringe-free lunar detail; f/7.7 supports rewarding high-magnification views |
| Saturn | Good Rings clearly defined, Cassini Division visible in steady seeing; 600mm focal length adequate for useful magnification with a short Barlow | Good Rings clearly defined, Cassini Division visible in good seeing; 625mm focal length limits image scale but clean optics compensate |
| Jupiter | Good Main equatorial belts and GRS visible; ED glass keeps the limb clean, but 80mm limits fine belt detail | Good Main equatorial belts and GRS visible with high contrast and no false colour; aperture limits finer belt detail |
| Mars | Challenging Small orange disc visible at opposition; polar cap hints possible but aperture too small for surface detail | Challenging Small disc visible at opposition with possible polar cap hint, but 81mm aperture cannot resolve surface albedo features |
Deep sky | ||
| Orion Nebula (M42) | Excellent 80mm aperture and 600mm focal length frame the full nebula with surrounding structure; trapezium resolved | Excellent 625mm focal length frames the nebula well; 81mm gathers enough light to show core structure and nebulosity wings |
| Andromeda Galaxy (M31) | Excellent 600mm focal length captures the full extent of the galaxy; bright core and inner dust lanes visible | Excellent 625mm focal length captures the galaxy's full extent; core and dust lanes visible, though outer halo is faint at 81mm |
| Open clusters | Excellent 600mm focal length gives wide true field — Pleiades, Double Cluster, and M35 all fit beautifully with pinpoint stars | Excellent Wide true field at 625mm beautifully frames clusters like the Pleiades and Double Cluster with pinpoint stars |
| Globular clusters | Moderate M13 and M3 appear as fuzzy concentrated balls; 80mm cannot resolve individual stars | Challenging 81mm cannot resolve individual stars — globulars appear as fuzzy, concentrated glows |
| Faint galaxies | Moderate Brighter Messier galaxies (M81/M82, M51) visible as faint smudges; no structure detail at 80mm | Moderate Brighter Messier galaxies visible as diffuse patches; 81mm lacks the light grasp for structure or fainter NGC 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 | Good 625mm focal length is moderately wide; rich starfields are enjoyable but the scope is too narrow for grand sweeping views |
Other | ||
| Double stars | Good Clean ED optics split Albireo easily and handle tighter pairs like Castor; Dawes limit ~1.45 arcsec | Good Clean optics and near-zero chromatic aberration make this a satisfying double star scope; Dawes limit around 1.4 arcseconds |
| Astrophotography (deep sky) | Not applicable | Not recommended No mount or tracking included; when paired with a suitable equatorial mount this would rate Excellent (81mm, f/7.7, superb correction) |
| Astrophotography (planetary) | Not applicable | Moderate Clean optics suit planetary capture, but 81mm aperture and 625mm focal length limit resolution and image scale |
The real tradeoff
Both scopes are capable. The question is which one fits the way you actually observe.
Vixen ED80Sf
- You'll spend £550 less upfront than the SD81S, leaving budget for a decent mount, eyepieces, and a diagonal — or you'll feel the sting of realising the OTA alone isn't enough.
- Your observing sessions reward wide-field sweeping: M42 with its full nebulous cocoon, Andromeda's halo, and jewel-box clusters fill the eyepiece cleanly without the colour fringing that cheaper refractors introduce.
- You'll pair this with a tracking mount when astrophotography calls, and at f/7.5 you'll find deep-sky targets like the North America Nebula reward even modest DSLR setups with sharp stars across the frame.
Vixen SD81S
- You'll pay £1199 for an OTA that handles lunar detail and planetary contrast at magnifications where 80mm would struggle, and you'll feel that difference the moment you centre Saturn's rings in steady seeing.
- Your observing sessions favour deliberate, high-power study over wide-field sweeping — the Moon's craters snap into focus with exceptional clarity, Jupiter's belts separate cleanly, and bright stars show no violet halo.
- You'll commit to the SD flattener (another £250–£350) when you're serious about imaging, but once it's in place, the flat field and lightweight OTA let smaller mounts track reliably through longer exposures of nebulae and galaxies.
The dark side
Every scope has a personality. Here’s where each one gets difficult.
Vixen
Vixen ED80Sf
Sold as OTA only — you must budget separately for mount, diagonal, finder, and eyepieces, making total system cost substantially higher than the quoted £649.
80mm aperture cannot resolve globular cluster structure, reveal faint galaxy detail, or show Mars as anything more than a featureless orange disc at opposition.
1.25" focuser limits your eyepiece selection and accessory compatibility compared to 2" refractor models at similar price points.
Vixen
Vixen SD81S
Sold as OTA only — no mount, finder, diagonal, or eyepiece included, so total system cost is substantially higher than the £1199 price tag.
81mm aperture hard-limits deep-sky and planetary performance; you'll see fuzzy patches where larger telescopes reveal globular cluster structure or fine planetary detail.
Vixen's proprietary dovetail and accessory system may require adapters for third-party mounts; the SD flattener/reducer (£250–£350) is essentially mandatory for serious imaging use, adding significant expense.
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 seeking a high-quality, portable wide-field refractor that excels at framing large nebulae and clusters whole, or if you're stepping into deep-sky astrophotography with a modest budget and willingness to assemble your own system. You'll regret it if you're a beginner expecting a complete ready-to-observe package, a planetary purist chasing Mars detail, or someone hoping 80mm will resolve faint galaxies.
The custom-rig optical tube
Vixen · Vixen SD81S
You'll love the SD81S if you're a demanding visual observer or astrophotographer who values optical purity, clean colour correction, and lightweight portability over raw aperture, and you have £1500+ to spend on a complete imaging or grab-and-go system. This isn't for you if you want to resolve fine planetary detail, chase faint deep-sky objects, or find an affordable ready-to-use package — 81mm is a hard aperture ceiling, and Vixen's proprietary system and premium pricing put it out of reach for budget-conscious beginners.
Our verdict
At £649 versus £1,199, the Vixen SD81S costs 85% more. It delivers 1mm more aperture — a real and visible advantage on faint targets.
If budget is a genuine constraint, the Vixen ED80Sf will make you a happy observer. The Vixen SD81S's optical advantage on faint targets is real and you are unlikely to regret it if you can stretch. If I had to choose without knowing your situation: start with the Vixen ED80Sf, use it for a year, then upgrade knowing exactly what you want.
Vixen ED80Sf
View Vixen ED80Sf →Vixen SD81S
View Vixen SD81S →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 | Vixen SD81S |
|---|---|---|
Apertureⓘ The most important spec — bigger = more light = better views | 80mm | 81mm |
Focal Length Longer = more magnification potential | 600mm | 625mm |
Focal Ratio Lower f-number = wider field of view; higher = more magnification per eyepiece | f/7.5 | f/7.72 |
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 SD (Super Duplex) glass doublet |
How do you point it?
| Spec | Vixen ED80Sf | Vixen SD81S |
|---|---|---|
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 | Vixen SD81S |
|---|---|---|
Focuser Size 2" accepts wider eyepieces and gives better low-power views | 2" | 2" |
Focuser Type Rack-and-pinion is standard; Crayford and dual-speed are smoother | Dual-speed Crayford (with 1.25" adapter) | Dual-speed Crayford (with 1.25" adapter) |
Size & weight
| Spec | Vixen ED80Sf | Vixen SD81S |
|---|---|---|
OTA Weightⓘ Optical tube only — useful for comparing mount load capacity | 1.8kg | 2kg |
Tube Length | 528mm | 540mm |
Tube Material | Aluminium | Aluminium |
What's in the box?
| Spec | Vixen ED80Sf | Vixen SD81S |
|---|---|---|
Diagonal Tilts the eyepiece 90° for comfortable viewing — useful on refractors |
Blue highlight: Vixen ED80Sf advantage · Amber highlight: Vixen SD81S advantage · Greyed cells: equal or subjective.