Telescope Comparison
Askar 103APO vs William Optics GT81
The price gap is real. The question is whether the extra capability is worth it at your stage.
First light
Askar · 103mm · £1,199
The custom-rig optical tube
- 103mm refractor — optical tube only, no mount included
- 700mm focal length at f/6.8
- 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
Askar 103APO gathers 1.6× 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
Askar 103APO'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. Askar 103APO's f/6.8 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)
William Optics GT81's optical tube is 1.3kg lighter. Relevant if you plan to use it on multiple mounts or carry the tube to dark-sky sites separately.
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 103APO | William Optics GT81 |
|---|---|---|
| Planets | ||
| Moon | Excellent 103mm aperture delivers sharp crater detail and clean terminator views; the ED triplet produces essentially no chromatic fringing on the bright limb | 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; 700mm focal length supports useful magnification but aperture limits fine banding detail | Moderate Rings clearly visible and colour-free, but 81mm aperture and 478mm focal length make the Cassini Division very difficult |
| Jupiter | Good Two main equatorial belts and GRS visible; 103mm resolves some secondary belts in good seeing but can't match larger apertures for fine atmospheric detail | Moderate Main equatorial belts visible in steady seeing; 81mm resolves limited banding detail and the Great Red Spot is marginal |
| Mars | Moderate Small disc visible with polar cap detectable near opposition; 103mm and 700mm focal length limit the detail available on this demanding target | Challenging Small orange disc visible at opposition; 81mm aperture insufficient to resolve surface features reliably |
Deep sky | ||
| Orion Nebula (M42) | Excellent 103mm gathers plenty of light and 700mm focal length frames the full nebula complex well; Trapezium resolved and nebulosity extends visually | Excellent Bright nebula easily visible; 478mm focal length at f/5.9 frames the full extent with surrounding nebulosity |
| Andromeda Galaxy (M31) | Excellent 700mm focal length keeps the full extent of M31 in the field; 103mm aperture shows the bright core and hints of dust lanes | Excellent 478mm focal length captures the core and dust lanes in a single wide field; aperture shows the inner halo structure |
| Open clusters | Excellent 700mm focal length and wide true field frame showpiece clusters like the Double Cluster and Pleiades beautifully | Excellent Wide-field sweet spot — Pleiades, Double Cluster, and M35 are beautifully framed with colour-free stars |
| Globular clusters | Moderate 103mm shows a granular, textured ball but cannot resolve individual stars in the core; M13 and M3 appear mottled at best | Challenging 81mm aperture shows globulars like M13 as fuzzy balls with no individual star resolution |
| Faint galaxies | Moderate 103mm aperture detects brighter Messier galaxies as smudges but struggles with fainter NGC targets visually | 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 700mm is slightly long for sweeping starfield views but still delivers rich fields; a reducer brings it closer to wide-field territory | Excellent 478mm at f/5.9 is ideal for sweeping rich star fields; low-power eyepieces deliver expansive true fields |
Other | ||
| Double stars | Good 103mm resolves doubles to about 1.1 arcsecond; f/6.8 is not ideal for high-magnification splitting but the clean optics help | 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 recommended No mount or tracking included; with a suitable equatorial mount this scope would rate Excellent — f/6.8, 103mm aperture, and ED triplet design are ideal for deep-sky imaging | 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) | Moderate 103mm aperture captures reasonable planetary detail with a high-speed camera, but aperture and focal length limit resolution compared to larger scopes | Challenging 81mm aperture and 478mm focal length produce a small planetary image scale; limited even with a Barlow |
| Emission nebulae (imaging) | Excellent 700mm at f/6.8 frames large emission nebulae like the Heart, Soul, and North America Nebula well on APS-C sensors; tight star correction across the field with a matched flattener | Not applicable |
| Galaxy groups (imaging) | Good 700mm focal length provides enough scale for galaxy groups like the Leo Triplet or M81/M82 on common sensor sizes while keeping good signal-to-noise at f/6.8 | Not applicable |
| 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.
Askar 103APO
- You'll frame medium-sized galaxies like the Leo Triplet and M81/M82 with enough focal length to actually resolve spiral arm structure — targets that look like vague smudges at 478mm.
- You'll need a beefier mount to carry the heavier tube, and your total imaging rig will comfortably exceed £3000 before you capture a single photon — but the data you get back will have tighter stars and fewer compromises at the edges of your sensor.
- You'll spend longer per sub-exposure than someone shooting at f/5.9, but the extra aperture gathers more light per frame, and you'll notice the difference on faint outer-arm detail in galaxies and dim Ha regions in nebulae.
William Optics GT81
- You'll be imaging the Veil Nebula complex, the North America Nebula, and M31's full extent in single frames that the 103APO's narrower field would need a mosaic to cover — and at f/5.9 your sub-exposures will be noticeably shorter.
- You'll get away with a lighter, cheaper equatorial mount, which means your total system cost stays well below what the 103APO demands and your setup time on a cold night drops significantly.
- You'll hit a hard ceiling on small targets — planetary nebulae, distant galaxy groups, and anything that needs focal length will look undersampled, and you'll find yourself wishing for more reach sooner than you expect.
The dark side
Every scope has a personality. Here’s where each one gets difficult.
Askar
Askar 103APO
At £1199 for the OTA alone — no mount, no diagonal, no eyepieces — you're realistically budgeting £3000+ for a complete imaging system before you've bought a single filter.
The f/6.8 focal ratio is a full stop slower than the GT81's f/5.9, which means meaningfully longer exposures to reach the same signal-to-noise on faint nebulosity.
You'll need a matched field flattener or reducer for acceptable edge-of-field stars on APS-C or larger sensors — that's another £150–300 accessory that isn't optional for serious work.
William Optics
William Optics GT81
At 81mm aperture, you're collecting 38% less light than the 103APO per unit time — faint galaxy detail and dim outer nebula regions will require substantially more integration time to compensate.
Some production runs lack a focuser lock, so if you're hanging a cooled camera and filter wheel off the back, you risk focuser slip mid-exposure — check your unit and budget for a fix if needed.
The 478mm focal length means planetary and lunar detail requires very short focal-length eyepieces or a Barlow to reach useful magnification, and even then 81mm of aperture simply can't resolve the Cassini Division or fine Jovian belt detail.
Which is right for you?
Two different buyers. Two different right answers.
The custom-rig optical tube
Askar · Askar 103APO
You've already been imaging with an 80mm refractor and you know you want more — more reach on galaxies, tighter stars, and the resolution to crop into your frames without everything falling apart. You're prepared to invest in a solid HEQ5-class mount and the full accessory chain, and you see the £3000+ total system cost as a deliberate step up rather than a nasty surprise. You want a single imaging platform that handles everything from large nebulae down to galaxy groups without needing a mosaic or feeling undersampled.
The custom-rig optical tube
William Optics · William Optics GT81
You're stepping into deep-sky astrophotography and you want a capable, portable imaging refractor that won't bankrupt you or demand a heavy-duty mount. You're drawn to the sweeping wide-field targets — the Veil, the North America Nebula, the full extent of M31 — and you'd rather frame them in one shot at f/5.9 than wrestle with mosaics. You accept that small, high-magnification targets aren't this scope's job, and you're happy to keep your total system lighter, cheaper, and faster to set up on any clear night.
Our verdict
At £699 versus £1,199, the Askar 103APO costs 72% more. It delivers 22mm more aperture — a real and visible advantage on faint targets.
If budget is a genuine constraint, the William Optics GT81 will make you a happy observer. The Askar 103APO'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 William Optics GT81, use it for a year, then upgrade knowing exactly what you want.
Askar 103APO
View Askar 103APO →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 | Askar 103APO | William Optics GT81 |
|---|---|---|
Apertureⓘ The most important spec — bigger = more light = better views | 103mm | 81mm |
Focal Length Longer = more magnification potential | 700mm | 478mm |
Focal Ratio Lower f-number = wider field of view; higher = more magnification per eyepiece | f/6.8 | 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 triplet on all air-to-glass surfaces | Fully multi-coated FMC ED triplet on all air-to-glass surfaces |
How do you point it?
| Spec | Askar 103APO | 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 | Askar 103APO | William Optics GT81 |
|---|---|---|
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" (10:1 reduction) | Dual-speed Crayford 2" (10:1 reduction fine focus) |
Size & weight
| Spec | Askar 103APO | William Optics GT81 |
|---|---|---|
OTA Weightⓘ Optical tube only — useful for comparing mount load capacity | 3.8kg | 2.5kg |
Tube Length | 550mm | 380mm |
Tube Material | Aluminium | Aluminium, anodised |
What's in the box?
| Spec | Askar 103APO | William Optics GT81 |
|---|---|---|
Diagonal Tilts the eyepiece 90° for comfortable viewing — useful on refractors |
Blue highlight: Askar 103APO advantage · Amber highlight: William Optics GT81 advantage · Greyed cells: equal or subjective.