Telescope Comparison
Askar 80PHQ vs William Optics FluoroStar 91
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
William Optics · 91mm · £1,299
The custom-rig optical tube
- 91mm refractor — optical tube only, no mount included
- 537mm 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 FluoroStar 91 gathers 1.3× 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
William Optics FluoroStar 91'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. William Optics FluoroStar 91's f/5.9 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 | William Optics FluoroStar 91 |
|---|---|---|
| Planets | ||
| Moon | Excellent 80mm aperture delivers sharp lunar detail; short focal length limits magnification but crater fields and terminator are crisp | Excellent 91mm aperture and fluorite correction deliver sharp, high-contrast lunar detail with no false colour on the limb |
| Saturn | Good Rings clearly visible at modest magnification; 448mm focal length limits high-power planetary detail | Good Ring structure and Cassini Division visible in good seeing, though short focal length requires high-power eyepieces to push magnification |
| Jupiter | Good Main cloud belts and Galilean moons visible, but the short focal length constrains useful magnification | Good Main cloud belts and GRS visible; 91mm resolves some detail but the 537mm focal length limits comfortable high-power use |
| Mars | Challenging Small disc visible at opposition; 80mm aperture and 448mm focal length insufficient to resolve surface features reliably | Challenging Disc visible at opposition with hints of albedo features, but 91mm aperture and short focal length make surface detail very difficult |
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 91mm aperture and 537mm focal length at f/5.9 frame the full nebula complex with bright, detailed nebulosity and resolved Trapezium |
| 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 537mm focal length captures the full extent of M31 including companion galaxies; 91mm aperture shows hints of outer halo structure |
| Open clusters | Excellent Wide field at 448mm frames large clusters like the Double Cluster, Pleiades, and Hyades superbly | Excellent Wide field at 537mm beautifully frames large clusters like the Double Cluster and Pleiades with tight, colour-free stars |
| Globular clusters | Moderate 80mm aperture shows bright globulars like M13 as granular but unresolved fuzzy patches | Moderate 91mm shows globulars as granular, concentrated balls — M13 has a bright core but individual stars remain unresolved |
| Faint galaxies | Moderate 80mm aperture detects brighter Messier galaxies as smudges; insufficient light grasp for dim NGC targets visually | Challenging 91mm gathers limited light for faint galaxies visually; brighter Messier galaxies visible as faint smudges, but detail is minimal |
| Milky Way / wide field | Excellent 448mm focal length at f/5.6 — ideal for sweeping rich star fields and Milky Way structure | Excellent 537mm at f/5.9 is ideal for rich Milky Way sweeps — star fields through Cygnus and Sagittarius are stunning |
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 91mm resolves wide and moderate doubles cleanly with excellent colour correction, though close pairs need very short eyepieces at this focal length |
| 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 — optically superb for deep-sky imaging but requires a separate equatorial mount to realise that potential |
| Astrophotography (planetary) | Challenging 80mm aperture and 448mm focal length undersized for planetary imaging; a Barlow helps but cannot overcome the aperture limit | Moderate 91mm and 537mm focal length are limited for planetary imaging; usable with a 2–3× Barlow on a tracking mount, but aperture constrains resolution |
| 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 |
| Emission nebulae (imaging) | Not applicable | Excellent Fast f/5.9 fluorite triplet excels at narrowband and broadband emission nebula imaging — Heart, Soul, North America, and Veil nebulae are ideal targets with a matched flattener |
The real tradeoff
Both scopes are capable. The question is which one fits the way you actually observe.
Askar 80PHQ
- You'll unbox it, mount it, and start imaging without ever shopping for a separate field flattener — the integrated quadruplet design means you're dialling in back-focus spacing, not hunting for compatible corrector optics, and that alone removes one of the most frustrating variables in astrophotography setup.
- You'll notice the f/5.6 speed shaving real minutes off your sub-exposures compared to the FluoroStar 91's f/5.9, and on narrowband filter nights that difference compounds — your signal-to-noise ratio climbs faster, letting you wrap up a session earlier or go deeper in the same time window.
- You'll feel the 80mm aperture limit when you try to image faint galaxy targets that need raw light grasp; the FluoroStar 91's extra 11mm of aperture collects roughly 29% more light, and on dim IFN or distant galaxy clusters you'll be stacking noticeably more frames to compensate.
William Optics FluoroStar 91
- You'll spend more on the optical train — the FluoroStar 91 demands a properly matched external field flattener or reducer for imaging, which means researching spacing, buying adapters, and shimming until edge stars are round — but that modularity also lets you swap between a flattener for native f/5.9 and a reducer for an even faster system.
- You'll appreciate the fluorite element most when you're processing tightly framed star fields or bright stars on narrowband data — colour halos that would demand post-processing correction with lesser glass simply aren't there, and that cumulative processing time savings matters across hundreds of imaging hours.
- You'll get meaningfully better visual side-trips than the 80PHQ offers; when you drop an eyepiece in between imaging runs, the 91mm fluorite triplet gives you a crisper, higher-contrast Moon, cleaner Saturn rings, and more resolved detail in M42 than the smaller scope can manage.
The dark side
Every scope has a personality. Here’s where each one gets difficult.
Askar
Askar 80PHQ
Back-focus spacing must be set to approximately 55mm with precision — get it wrong by even a millimetre or two and you'll see field curvature and elongated stars creeping into the corners, which is maddening to diagnose if you don't own calipers and spacer rings.
Some users report the stock focuser flexes under heavier camera payloads; if you're running a full-frame cooled camera with a filter wheel, you may find yourself budgeting for an aftermarket focuser upgrade on top of the £799 OTA price.
At 80mm aperture, light grasp is the fundamental ceiling — no amount of integration time fully compensates for the photon deficit compared to the 91mm FluoroStar, and on faint extended targets you'll feel that gap in your final stacks.
William Optics
William Optics FluoroStar 91
The premium you're paying for natural fluorite over quality FPL-53 ED glass delivers a visually marginal difference — if you're not doing demanding long-exposure astrophotography, the extra £500 over the 80PHQ is buying colour correction you may never actually perceive.
Without a matched field flattener, the FluoroStar 91 produces elongated stars at the edges of APS-C and especially full-frame sensors — this is an additional purchase and spacing calibration the 80PHQ's integrated quadruplet design simply eliminates.
The 537mm focal length still limits high-magnification visual use; pushing planetary detail requires very short focal-length eyepieces or a Barlow, and even then 91mm of aperture can't compete with larger instruments for Jupiter or Saturn detail.
Which is right for you?
Two different buyers. Two different right answers.
The custom-rig optical tube
Askar · Askar 80PHQ
You want the fastest, most hassle-free path from unboxing to imaging. You're building a portable deep-sky rig around a mid-range equatorial mount, you don't want to research and buy a separate field flattener, and you'd rather put the £500 you save toward a better mount, guide camera, or filters. You shoot wide-field nebulae and Milky Way star fields more than small galaxies, and you accept that 80mm of aperture means longer total integration on faint targets. Visual observing is an occasional bonus, not a priority.
The custom-rig optical tube
William Optics · William Optics FluoroStar 91
You're an experienced imager who's already fought the back-focus and flattener battles and won — you know how to space a corrector, you own the adapters, and you want the best possible colour correction a compact refractor can deliver. You're willing to pay the fluorite premium because you've seen what chromatic aberration does to your star profiles across hundreds of stacked subs, and you want to eliminate it at the source. The extra 11mm of aperture matters to you for faint targets, and you value the option of genuinely enjoyable visual side-trips that the 80PHQ can't quite match.
Our verdict
At £799 versus £1,299, the William Optics FluoroStar 91 costs 63% more. It delivers 11mm 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 William Optics FluoroStar 91'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 →William Optics FluoroStar 91
View William Optics FluoroStar 91 →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 | William Optics FluoroStar 91 |
|---|---|---|
Apertureⓘ The most important spec — bigger = more light = better views | 80mm | 91mm |
Focal Length Longer = more magnification potential | 448mm | 537mm |
Focal Ratio Lower f-number = wider field of view; higher = more magnification per eyepiece | f/5.6 | 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 PHQ quadruplet on all surfaces | Fully multi-coated fluorite triplet on all air-to-glass surfaces |
How do you point it?
| Spec | Askar 80PHQ | William Optics FluoroStar 91 |
|---|---|---|
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 | William Optics FluoroStar 91 |
|---|---|---|
Focuser Size 2" accepts wider eyepieces and gives better low-power views | 2" / 1.25" | 2" / 1.25" |
Focuser Type Rack-and-pinion is standard; Crayford and dual-speed are smoother | Dual-speed Crayford 2" (with 1.25" adapter) | Dual-speed Crayford 2" (10:1 reduction fine focus) |
Size & weight
| Spec | Askar 80PHQ | William Optics FluoroStar 91 |
|---|---|---|
OTA Weightⓘ Optical tube only — useful for comparing mount load capacity | 2.8kg | 3.2kg |
Tube Length | 360mm | 430mm |
Tube Material | Aluminium | Aluminium, anodised |
What's in the box?
| Spec | Askar 80PHQ | William Optics FluoroStar 91 |
|---|---|---|
Diagonal Tilts the eyepiece 90° for comfortable viewing — useful on refractors |
Blue highlight: Askar 80PHQ advantage · Amber highlight: William Optics FluoroStar 91 advantage · Greyed cells: equal or subjective.