Sky-Watcher Flextube 400P SynScan GoTo Collapsible Dobsonian — image 1
Sky-Watcher

Sky-Watcher Flextube 400P SynScan GoTo Collapsible Dobsonian

Sixteen inches of aperture, the deepest the Flextube line goes, with GoTo tracking. A near-observatory light bucket that still collapses for transport, for the observer who wants to chase the faintest galaxies and see planetary detail direct.

84/ 100
Polaris Score
#1 of 1 16" GoTo Dobsonian
See the breakdown ↓
Aperture
406mm
Focal Length
1800mm
Focal Ratio
f/4.4
Mount Type
Dobsonian (GoTo)
Optical Design
Dobsonian
Weight
80.3 kg
From$4,499

Lowest in 90 daysLowest ever tracked

Price tracked by PolarisObserved 93 timesTracking since Jul 2026

Try in simulator →
What it's built forOpen these in the simulator →

This telescope was built to gather light.

406 mm of aperture pulls in the faint light that galaxies and clusters live or die on. Point it up under a dark sky and objects that are rumors in smaller scopes resolve into real structure.

Sweet spot 300–510×Rewards dark skies
The view people remember

The Whirlpool, and its companion.

A face-on spiral with a smaller galaxy caught at the end of one arm — on a dark night the spiral structure lifts off the sky in a way photographs almost prepare you for.

See Whirlpool Galaxy through this telescope →
01What it's good at

What it's best at — and the trade-offs.

406mm gathers more than 2.5x the light of a 10-inch, enough to show galaxy structure and faint planetary nebulae with a directness smaller scopes only…
Best at
✓406mm gathers more than 2.5x the light of a 10-inch, enough to show galaxy structure and faint planetary nebulae with a directness smaller scopes only hint at
✓SynScan GoTo motorizes both axes: align on a few stars and it slews to and tracks any of 42,000+ objects, so a big Dob stops being a hunt and starts being a tour
✓The Flextube truss collapses the tube for transport, then extends and holds collimation, the only way a scope this size fits in a normal car
✓It keeps the Dobsonian payoff intact: aperture-per-dollar nothing else touches, on a stable, intuitive alt-az base
Trade-offs
!It's heavy and bulky: plan on a two-part carry and, at the larger sizes, help or a wheeled setup
!The GoTo base needs stable power (a battery pack or supply) that a manual Dob does not
!The open truss lets stray light and dust reach the mirror, so a shroud helps at real sites
!At f/4.4 it's demanding on eyepieces and shows edge coma without a corrector; alt-az tracking suits visual use, not imaging
02In plain English

What These Numbers Mean

406mm · f/4.4 · 1800mm FL · Dobsonian (GoTo)
Aperture
406 mm (16 inch)
Sixteen inches gathers roughly 3,300 times the light of your eye. This is observatory territory: hundreds of galaxies with visible structure, planetary nebulae showing colour, and detail on Mars and Jupiter limited by the atmosphere rather than by the telescope.
Focal length
1800 mm
Long focal length with enormous light grasp behind it, so 400x is usable whenever the seeing allows. A 30 mm eyepiece still gives 60x with a genuinely wide true field.
Focal ratio
f/4.4
Very fast for a large Newtonian, which is what keeps the tube short enough to use without scaffolding. At this speed a coma corrector and premium eyepieces are required rather than optional.
Optical design
Collapsible truss Newtonian
The collapsing truss is the only thing that makes 16 inches transportable, but the mirror is large enough that collimation, cooling and a shroud all become mandatory parts of the routine.
Weight
73 kg total
About 160 lb across tube and base. This is a two-person telescope in every sense, best treated as a semi-permanent installation with a trolley for the last few metres.
Cooldown
90 minutes or more
A 16 inch mirror stores a great deal of heat and releases it slowly, and the resulting air currents blur exactly the fine detail this aperture exists to show. Fans and an early start are standard practice at this size.
03The Polaris Score

How it scores, and why.

84/100 · #1 of 1 16" GoTo Dobsonian
84/ 100
Sky-Watcher Flextube 400P SynScan GoTo Collapsible Dobsonian
#1 of 1 16" GoTo Dobsonian
Performance
95
Ease of use
70
Portability
30
Upgrade potential
50

Polaris weighs optical capability, how easy the scope is to live with, how portable it is, and how far it takes you before you outgrow it — not list price or brand.

04Who it's for

An honest fit check.

Deep-sky observers who want 16" of light-grasp and let the mount find and track objects for…
Buy it if you
✓Deep-sky observers who want 16" of light-grasp and let the mount find and track objects for them
✓Anyone chasing faint galaxies, globulars, and planetary nebulae that smaller scopes only hint at
✓Observers with the space and a way to move a large two-part scope who want maximum aperture without a permanent pier
Look elsewhere if you
!Anyone who needs a light, one-hand grab-and-go setup, this is a deliberate haul
!Deep-sky imagers, since an alt-az Dob base can't do long exposures
!Observers short on storage or without a way to transport a bulky base and tube
05Build your rig

What to buy next — and where it leads.

8 pieces of gear, ordered by what changes the view most
Recommended upgrades
See wider, brighter deep-sky views★ Top pickExplore Scientific 68deg 28mm 2-inch

Commonly paired with Sky-Watcher Flextube 400P SynScan GoTo Collapsible Dobsonian

Pinpoint stars across the whole fieldApertura 1x Photographic Coma Corrector

Sharpens stars to the very edge of the field at fast focal ratios

Make nebulae popOptolong UHC Filter 2″

Improves contrast on nebulae and planets with this setup

Observe better
Tame lunar glareGSO Moon Filter 13pct 1.25-inch

Improves contrast on nebulae and planets with this setup

Make nebulae popSVBony UHC 1.25-inch

Commonly paired with this telescope

Sharper planets & lunar detailCelestron X-Cel LX 7mm

Commonly paired with this telescope

A sharper everyday viewCelestron X-Cel LX 18mm

Commonly paired with this telescope

Show all compatible gear (5) →
Accessories
Double your magnificationTele Vue 2x Barlow 1.25-inch

Doubles magnification for closer planetary detail with this telescope

Lunar & planetary
Excellent
Deep-sky visual
Excellent
Astrophotography
Not its purpose, a visual scope
06The numbers

Full specifications.

6 measured and stated values
Optics
Optical DesignDobsonian
Aperture406mm
Focal Length1800mm
Focal Ratiof/4.4
Mount & drive
Mount TypeDobsonian (GoTo)
Physical
Weight80.3 kg
07Alternatives

For a different goal, start here.

3 alternatives, each mapped to the goal it wins at
Lighter & cheaper

Sky-Watcher Flextube 350P SynScan GoTo Collapsible Dobsonian

The 14-inch gives up little reach and is far more manageable to move and store

→
Still transportable

Sky-Watcher Flextube 300P SynScan GoTo Collapsible Dobsonian

The 12-inch is a serious scope that one determined person can still handle

→
Sweet spot

Sky-Watcher Flextube 250P SynScan GoTo Collapsible Dobsonian

The 10-inch if maximum aperture isn't worth a two-person, heavy-crate setup

→
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