Telescope Comparison
Sky-Watcher Esprit 100ED vs Sky-Watcher Esprit 120ED
The price gap is real. The question is whether the extra capability is worth it at your stage.
First light
Sky-Watcher · 100mm · £1,099
The custom-rig optical tube
- 100mm refractor — optical tube only, no mount included
- 550mm focal length at f/5.5
- 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
Sky-Watcher · 120mm · £1,699
The custom-rig optical tube
- 120mm refractor — optical tube only, no mount included
- 840mm focal length at f/7
- 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
Sky-Watcher Esprit 120ED gathers 1.4× 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
Sky-Watcher Esprit 120ED's longer focal length reaches higher magnification with the same eyepiece — better reach for planetary detail. Sky-Watcher Esprit 100ED's shorter focal length gives a wider true field — better for large open clusters and extended nebulae.
Focal ratio
Sky-Watcher Esprit 100ED's faster f/5.5 delivers wider fields with any eyepiece — better for open clusters and large nebulae. Sky-Watcher Esprit 120ED's f/7 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)
Sky-Watcher Esprit 100ED's optical tube is 1.8kg 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 | Sky-Watcher Esprit 100ED | Sky-Watcher Esprit 120ED |
|---|---|---|
| Planets | ||
| Moon | Excellent 100mm aperture delivers sharp crater detail and clean terminator views; the fast focal ratio means lower magnification per eyepiece but detail is still crisp | Excellent 120mm apochromatic optics deliver razor-sharp lunar detail with zero chromatic aberration — craterlets and rilles cleanly resolved |
| Saturn | Good Rings clearly separated, Cassini Division visible in good seeing; 550mm focal length limits image scale at the eyepiece | Good 120mm aperture and 840mm focal length show rings, Cassini Division in steady seeing, and subtle banding on the disc |
| Jupiter | Good Two main cloud belts and GRS visible; 100mm aperture resolves belt detail but the short focal length caps useful magnification | Good Cloud bands, Great Red Spot, and moon transits visible — the clean apo optics give high contrast, though aperture limits finest detail |
| Mars | Moderate Disc and polar cap visible at opposition; 100mm and 550mm focal length are limiting for surface albedo features | Moderate Disc visible with polar cap and dark albedo features at opposition, but 120mm limits fine surface detail |
Deep sky | ||
| Orion Nebula (M42) | Excellent 100mm gathers ample light, 550mm frames the full nebula with surrounding nebulosity; f/5.5 rewards both visual and imaging use | Excellent 120mm aperture reveals nebulosity easily; 840mm focal length frames the core and wings well on camera or in a wide-field eyepiece |
| Andromeda Galaxy (M31) | Excellent 550mm captures the full extent of M31 including companion galaxies; 100mm aperture shows outer halo hints visually | Good 840mm focal length captures the bright core and inner spiral arms but crops the full 3° extent on most sensors and eyepieces |
| Open clusters | Excellent 550mm focal length provides generous framing — the Double Cluster, Pleiades, and similar targets are beautifully presented | Good 840mm gives a pleasing field for medium-sized clusters like M35 and the Double Cluster, though the largest clusters may not fully fit |
| Globular clusters | Moderate M13 and M5 appear granular with hints of edge resolution; core remains unresolved at 100mm | Moderate 120mm resolves granularity at the edges of brighter globulars like M13, but the core remains unresolved |
| Faint galaxies | Moderate 100mm shows brighter Messier galaxies as fuzzy patches; NGC targets require dark skies and are at the limit visually | Moderate 120mm gathers enough light to detect many Messier and brighter NGC galaxies, but faint detail requires long imaging exposures |
| Milky Way / wide field | Good 550mm is slightly long for sweeping Milky Way panoramas but still delivers rich star fields; excellent for targeted regions like Cygnus | Moderate 840mm focal length is too narrow for sweeping Milky Way vistas — better suited to individual targets within it |
Other | ||
| Double stars | Good 100mm resolves down to about 1.2 arcsec; chromatic correction is excellent but the fast focal ratio makes splitting tight pairs trickier than in a long-focus refractor | Excellent 120mm aperture resolves to ~1 arcsecond; the apochromatic design produces clean, colour-free Airy discs ideal for tight doubles |
| Astrophotography (deep sky) | Not recommended No mount included — on a suitable equatorial GoTo mount this scope would rate Excellent (f/5.5, 100mm, flat field to full-frame), but as sold it cannot track | Not applicable |
| Astrophotography (planetary) | Moderate 100mm aperture is workable with a Barlow and planetary camera, but 550mm native focal length requires significant amplification; needs a tracking mount | Moderate 120mm aperture limits planetary resolution compared to larger scopes; 840mm native focal length benefits from a 2–3× Barlow for better image scale |
| Emission nebulae (imaging) | Excellent Fast f/5.5 ratio and 550mm focal length are ideal for large emission targets like the Veil, Rosette, and Heart Nebulae on APS-C or full-frame sensors | Not applicable |
| Galaxy groups (imaging) | Good 550mm frames targets like the Leo Triplet and Markarian's Chain well on APS-C; 100mm gathers enough light for reasonable exposure times | Not applicable |
| Compact emission and planetary nebulae | Not applicable | Excellent 840mm focal length and f/7 speed are ideal for imaging targets like the Crescent Nebula, Veil Nebula panels, and the Dumbbell Nebula |
The real tradeoff
Both scopes are capable. The question is which one fits the way you actually observe.
Sky-Watcher Esprit 100ED
- At 550mm and f/5.5, you'll capture the entire Veil Nebula complex or the full extent of Andromeda in a single APS-C frame — your target list skews toward large nebulae and sweeping star fields rather than individual galaxies.
- Your fully loaded imaging train tops out around 6–7kg, which means you can run this on a mid-range mount like an HEQ5 and still have headroom — you're spending less on the mount and spending less time fighting flexure.
- You'll gather light faster per sub-exposure than the 120ED, so your total integration times shrink — but if you ever try narrowband on a full-frame sensor, you may wrestle with filter halos and uneven illumination that the wider cone at f/5.5 can introduce.
Sky-Watcher Esprit 120ED
- At 840mm and f/7, you'll frame galaxies like M51 and the Leo Triplet with noticeably more image scale — you're resolving spiral arms and detail that the 100ED simply can't pull out of the same integration time, and you'll find yourself reaching for galaxy season targets more often.
- You'll need a mount rated for 10–12kg imaging payloads, which means an EQ6-R class or better — that's a bigger investment, a heavier setup in the car, and more time getting balanced and polar aligned before your first exposure.
- The extra 20mm of aperture and the slower f/7 cone give you a more forgiving back-focus tolerance and cleaner narrowband performance across full-frame sensors, but you're paying for that with longer individual sub-exposures to reach the same signal-to-noise ratio.
The dark side
Every scope has a personality. Here’s where each one gets difficult.
Sky-Watcher
Sky-Watcher Esprit 100ED
The integrated field flattener demands exactly 55mm of back-focus spacing — get it wrong by even a couple of millimetres and your edge stars will streak, turning your first few sessions into a frustrating shimming exercise.
At f/5.5, some narrowband filters produce halos or uneven illumination across full-frame sensors, which can force you to crop to APS-C or spend time in post correcting gradients.
No mount, finder, diagonal, or eyepiece is included — after adding a capable equatorial mount and imaging accessories, your total spend typically reaches £2,500–£3,000+, more than double the OTA price.
Sky-Watcher
Sky-Watcher Esprit 120ED
At 5.5kg bare and 7–8kg fully loaded, you need a substantial equatorial mount — an undersized mount will produce poor tracking and guiding, and there's no cheating the payload requirement.
The dew shield retraction mechanism has been reported to stiffen in cold conditions, which can be an annoyance when you're trying to pack up at 3am in winter.
Total system cost with a suitable mount, camera, and accessories typically exceeds £4,000 — this is a serious financial commitment before you've captured a single photon.
Which is right for you?
Two different buyers. Two different right answers.
The custom-rig optical tube
Sky-Watcher · Sky-Watcher Esprit 100ED
You'll love the Esprit 100ED if you're stepping up from an 80mm ED doublet and want a genuine imaging upgrade without overhauling your entire mount and accessory chain. You want to shoot large emission nebulae and wide star fields on APS-C or full-frame, and you value the faster f/5.5 speed for shorter sub-exposures on broadband targets. You already own an HEQ5-class mount and you're not ready to invest in a heavier platform. This isn't for you if you're a beginner expecting a complete ready-to-use system, or if your target list leans toward smaller galaxies and planetary nebulae that need more image scale than 550mm can deliver.
The custom-rig optical tube
Sky-Watcher · Sky-Watcher Esprit 120ED
You'll love the Esprit 120ED if you're an experienced imager who's done the wide-field thing and now wants to resolve more detail in galaxies and mid-sized deep-sky targets without switching to a reflector. You already own or are prepared to buy a serious equatorial mount in the EQ6-R class, and the total £4,000+ system cost doesn't make you flinch — you see it as a long-term imaging platform. This isn't for you if you're budget-conscious and hoping to build a complete rig affordably, or if you prioritise portability and quick setup over image scale and aperture.
Our verdict
At £1,099 versus £1,699, the Sky-Watcher Esprit 120ED costs 55% more. It delivers 20mm more aperture — a real and visible advantage on faint targets.
If budget is a genuine constraint, the Sky-Watcher Esprit 100ED will make you a happy observer. The Sky-Watcher Esprit 120ED'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 Sky-Watcher Esprit 100ED, use it for a year, then upgrade knowing exactly what you want.
Sky-Watcher Esprit 100ED
View Sky-Watcher Esprit 100ED →Sky-Watcher Esprit 120ED
View Sky-Watcher Esprit 120ED →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 | Sky-Watcher Esprit 100ED | Sky-Watcher Esprit 120ED |
|---|---|---|
Apertureⓘ The most important spec — bigger = more light = better views | 100mm | 120mm |
Focal Length Longer = more magnification potential | 550mm | 840mm |
Focal Ratio Lower f-number = wider field of view; higher = more magnification per eyepiece | f/5.5 | f/7 |
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 with FMC on all air-to-glass surfaces | Fully multi-coated ED triplet with FMC on all air-to-glass surfaces |
How do you point it?
| Spec | Sky-Watcher Esprit 100ED | Sky-Watcher Esprit 120ED |
|---|---|---|
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 | Sky-Watcher Esprit 100ED | Sky-Watcher Esprit 120ED |
|---|---|---|
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 (10:1 reduction, with 1.25" adapter) | Dual-speed Crayford (10:1 reduction, with 1.25" adapter) |
Size & weight
| Spec | Sky-Watcher Esprit 100ED | Sky-Watcher Esprit 120ED |
|---|---|---|
OTA Weightⓘ Optical tube only — useful for comparing mount load capacity | 3.9kg | 5.7kg |
Tube Length | 535mm | 730mm |
Tube Material | Aluminium, white powder coat | Aluminium, white powder coat |
What's in the box?
| Spec | Sky-Watcher Esprit 100ED | Sky-Watcher Esprit 120ED |
|---|---|---|
Diagonal Tilts the eyepiece 90° for comfortable viewing — useful on refractors |
Blue highlight: Sky-Watcher Esprit 100ED advantage · Amber highlight: Sky-Watcher Esprit 120ED advantage · Greyed cells: equal or subjective.