Telescope Comparison
Askar 80PHQ vs Vixen SD81S
The price gap is real. The question is whether the extra capability is worth it at your stage.
First light
Askar · 80mm · £799
The custom-rig optical tube
- 80mm refractor — optical tube only, no mount included
- 448mm focal length at f/5.6
- 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
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. Askar 80PHQ's shorter focal length gives a wider true field — better for large open clusters and extended nebulae.
Focal ratio
Askar 80PHQ's faster f/5.6 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 | Askar 80PHQ | Vixen SD81S |
|---|---|---|
| Planets | ||
| Moon | Excellent 80mm aperture delivers sharp lunar detail; short focal length limits magnification but crater fields and terminator are crisp | 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 visible at modest magnification; 448mm focal length limits high-power planetary detail | Good Rings clearly defined, Cassini Division visible in good seeing; 625mm focal length limits image scale but clean optics compensate |
| Jupiter | Good Main cloud belts and Galilean moons visible, but the short focal length constrains useful magnification | Good Main equatorial belts and GRS visible with high contrast and no false colour; aperture limits finer belt detail |
| Mars | Challenging Small disc visible at opposition; 80mm aperture and 448mm focal length insufficient to resolve surface features reliably | 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 Bright target framed beautifully by the wide field; f/5.6 speed and sub-600mm focal length show full nebula extent | Excellent 625mm focal length frames the nebula well; 81mm gathers enough light to show core structure and nebulosity wings |
| Andromeda Galaxy (M31) | Excellent 448mm focal length captures the full extent of M31 including outer halo; 80mm aperture adequate for the bright core and dust lanes | 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 Wide field at 448mm frames large clusters like the Double Cluster, Pleiades, and Hyades superbly | Excellent Wide true field at 625mm beautifully frames clusters like the Pleiades and Double Cluster with pinpoint stars |
| Globular clusters | Moderate 80mm aperture shows bright globulars like M13 as granular but unresolved fuzzy patches | Challenging 81mm cannot resolve individual stars — globulars appear as fuzzy, concentrated glows |
| Faint galaxies | Moderate 80mm aperture detects brighter Messier galaxies as smudges; insufficient light grasp for dim NGC targets visually | Moderate Brighter Messier galaxies visible as diffuse patches; 81mm lacks the light grasp for structure or fainter NGC targets |
| Milky Way / wide field | Excellent 448mm focal length at f/5.6 — ideal for sweeping rich star fields and Milky Way structure | 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 80mm resolves wider doubles cleanly; the fast f/5.6 focal ratio is less ideal than a long-FL refractor for tight pairs | 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 recommended OTA only with no mount — requires a separate equatorial or GoTo mount for any deep-sky imaging; on a suitable mount this would rate Excellent | 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) | Challenging 80mm aperture and 448mm focal length undersized for planetary imaging; a Barlow helps but cannot overcome the aperture limit | Moderate Clean optics suit planetary capture, but 81mm aperture and 625mm focal length limit resolution and image scale |
| Wide-field emission nebulae (imaging) | Excellent Fast f/5.6 quad APO with integrated flattener is purpose-built for targets like the Veil, North America, and Rosette Nebulae on a suitable mount | Not applicable |
The real tradeoff
Both scopes are capable. The question is which one fits the way you actually observe.
Askar 80PHQ
- You'll attach your camera, nail the 55mm back-focus spacing, and start shooting — the integrated quad-element field flattener means no separate corrector to buy, space, or tilt-adjust, and stars stay pinpoint right into the corners of a full-frame sensor out of the box.
- At f/5.6 you're gathering light noticeably faster than the SD81S at f/7.7, which means your sub-exposures can be roughly half the length for the same signal — on a winter night shooting the Rosette Nebula in narrowband, that speed difference is the difference between finishing at midnight and finishing at 2am.
- You'll rarely put an eyepiece in this scope; its 448mm focal length gives such low magnification that planets are tiny and underwhelming, so your observing sessions are camera-first, always.
Vixen SD81S
- You'll actually enjoy visual nights with this scope — the SD glass delivers a clean, virtually fringe-free lunar limb and crisp planetary views that make the 80PHQ's visual performance feel like an afterthought, so you can split your time between imaging and eyepiece observing without feeling shortchanged.
- You'll need to budget an extra £250–£350 for Vixen's dedicated SD flattener before you can image seriously, and you'll have to nail the spacing yourself, whereas the 80PHQ's integrated flattener eliminates that entire step and cost.
- At f/7.7 and 625mm focal length, you're working at a noticeably slower and longer focal length — your framing of large nebula complexes will be tighter and your exposures longer, but you gain a more forgiving image scale that's less punishing of guiding errors and focus shifts.
The dark side
Every scope has a personality. Here’s where each one gets difficult.
Askar
Askar 80PHQ
The 55mm back-focus distance must be precisely maintained — get the spacing wrong by even a millimetre or two and you'll see field curvature and elongated stars in the corners, turning the integrated flattener's convenience into a frustrating debugging exercise.
Some users report the stock focuser struggles under heavy camera payloads, and while it handles most setups adequately, a serious full-frame rig with filter wheel and off-axis guider may justify an aftermarket focuser upgrade.
At £799 for the OTA alone with no mount, finder, diagonal, or eyepiece, your total imaging system cost — including a decent EQ mount, guide scope, and cameras — will be several times the sticker price.
Vixen
Vixen SD81S
Vixen's proprietary dovetail and accessory system means you'll likely need adapters to fit third-party mounts and accessories — an annoying extra step and cost that the Askar's more standard setup avoids.
The SD81S is a two-element SD doublet, not a triplet or quadruplet — its colour correction is excellent but not truly apochromatic across the full spectrum, and for imaging you're essentially required to buy the separate SD flattener at £250–£350 on top of the already-higher £1,199 OTA price.
At £1,199 before any accessories, you're paying a significant premium for the Vixen name and SD glass — comparable 80mm ED doublets from other manufacturers offer similar aperture and performance for considerably less.
Which is right for you?
Two different buyers. Two different right answers.
The custom-rig optical tube
Askar · Askar 80PHQ
You're a dedicated astrophotographer who wants a compact, fast imaging refractor that's ready to shoot with minimal accessory fuss. You'll pair this with an equatorial mount and autoguider, you already own or plan to buy the rest of the imaging chain, and you have zero interest in visual observing — you want flat-field, pinpoint stars across a full-frame sensor without buying and spacing a separate corrector. If you're chasing large emission nebulae and widefield mosaics and every minute of integration time matters, the 80PHQ's f/5.6 speed and integrated optics justify themselves quickly. This is not for you if you want any kind of visual capability, or if you're a beginner hoping one purchase gets you observing tonight.
The custom-rig optical tube
Vixen · Vixen SD81S
You're an experienced observer or imager who values optical purity and wants a scope that genuinely pulls double duty — sharp, colour-free views of the Moon and planets on visual nights, and a capable widefield imaging platform when paired with the dedicated flattener. You're comfortable paying a premium for Vixen's build quality and SD glass, and the extra cost and spacing work of adding the flattener doesn't bother you because you appreciate the flexibility of a scope that rewards both your eye and your camera. This isn't for you if you're purely an imager on a budget — the 80PHQ delivers faster, flatter imaging performance for £400 less with the flattener already built in.
Our verdict
At £799 versus £1,199, the Vixen SD81S costs 50% more. It delivers 1mm more aperture — a real and visible advantage on faint targets.
If budget is a genuine constraint, the Askar 80PHQ 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 Askar 80PHQ, use it for a year, then upgrade knowing exactly what you want.
Askar 80PHQ
View Askar 80PHQ →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 | Askar 80PHQ | Vixen SD81S |
|---|---|---|
Apertureⓘ The most important spec — bigger = more light = better views | 80mm | 81mm |
Focal Length Longer = more magnification potential | 448mm | 625mm |
Focal Ratio Lower f-number = wider field of view; higher = more magnification per eyepiece | f/5.6 | 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 PHQ quadruplet on all surfaces | Fully multi-coated SD (Super Duplex) glass doublet |
How do you point it?
| Spec | Askar 80PHQ | 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 | Askar 80PHQ | Vixen SD81S |
|---|---|---|
Focuser Size 2" accepts wider eyepieces and gives better low-power views | 2" / 1.25" | 2" |
Focuser Type Rack-and-pinion is standard; Crayford and dual-speed are smoother | Dual-speed Crayford 2" (with 1.25" adapter) | Dual-speed Crayford (with 1.25" adapter) |
Size & weight
| Spec | Askar 80PHQ | Vixen SD81S |
|---|---|---|
OTA Weightⓘ Optical tube only — useful for comparing mount load capacity | 2.8kg | 2kg |
Tube Length | 360mm | 540mm |
Tube Material | Aluminium | Aluminium |
What's in the box?
| Spec | Askar 80PHQ | Vixen SD81S |
|---|---|---|
Diagonal Tilts the eyepiece 90° for comfortable viewing — useful on refractors |
Blue highlight: Askar 80PHQ advantage · Amber highlight: Vixen SD81S advantage · Greyed cells: equal or subjective.