William Optics ZenithStar 73 APO Doublet — image 1
William Optics

William Optics ZenithStar 73 APO Doublet

No longer sold

A 73mm f/5.9 ED doublet that hits the popular grab-and-shoot wide-field imaging class, pairing William Optics build quality with a friendly price and a light, portable tube.

86/ 100
Polaris Score
#2 of 8 compact imaging refractor
See the breakdown ↓
Aperture
73mm
Focal Length
430mm
Focal Ratio
f/5.9
Mount Type
None (OTA only)
Optical Design
ED Doublet Refractor
Weight
3 kg
Try in simulator →
No longer sold

Discontinued by the manufacturer (per Agena Astro). We keep the page for reference — see current alternatives below.

See alternatives ↓
What it's built forOpen these in the simulator →

This telescope was built for sweeping wide.

A short, fast refractor with a generous true field — the whole sword of Orion in one view, star fields that spill past the field stop. It rewards low power and dark skies far more than chasing magnification.

Widest true fieldsTack-sharp to the edge
The view people remember

The Orion Nebula, wings unfolded.

The four stars of the Trapezium sit inside folded sheets of glowing gas — the closest stellar nursery to us, bright enough to show real structure even from the suburbs.

See Orion Nebula through this telescope →
01What it's good at

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

The FPL-53 ED doublet controls color well for its price, keeping stars clean across the field with a flattener
Best at
✓The FPL-53 ED doublet controls color well for its price, keeping stars clean across the field with a flattener
✓430mm at f/5.9 frames large nebulae and the Milky Way, an ideal wide-field imaging focal length
✓At about 3kg it rides on small trackers and mounts, keeping the whole rig portable
✓William Optics fit and finish make it feel more premium than its price
Trade-offs
!A matched flattener is a separate purchase for the flattest stars when imaging
!As a doublet it shows slightly more residual color than a triplet
!73mm and 430mm keep small targets small in the frame
!It is an OTA only and needs a mount, diagonal or camera to work
02In plain English

What These Numbers Mean

73mm · f/5.9 · 430mm FL
Aperture
73 mm
Just under three inches, gathering about 43 percent more light than a 61 mm. That is a meaningful reduction in the integration time needed for the same image quality.
Focal length
430 mm
Wide field with slightly more scale than the smaller ZenithStars. Large nebulae fit an APS-C frame while the brighter galaxies keep enough size to be worth processing.
Focal ratio
f/5.9
Fast enough for practical exposure times and short enough that guiding demands stay light. A forgiving combination for anyone still learning the imaging workflow.
Optical design
ED doublet apochromat
Two elements with ED glass control colour well at this speed, keeping stars tight without the weight or cost of a triplet. Add the matching flattener for clean corners.
Weight
3 kg tube
About 6.6 lb, which a small equatorial or a well-loaded star tracker handles. It stays a one-case travel telescope.
Mount
OTA only
No mount included. A tracker or entry-level equatorial with basic guiding suits it, keeping the total cost of a complete setup low.
03The Polaris Score

How it scores, and why.

86/100 · #2 of 8 compact imaging refractor
86/ 100
William Optics ZenithStar 73 APO Doublet
#2 of 8 compact imaging refractor
Performance
85
Ease of use
80
Portability
90
Upgrade potential
80

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.

Imagers wanting a portable, affordable wide-field apo
Buy it if you
✓Imagers wanting a portable, affordable wide-field apo
✓People who want one light tube for imaging and casual visual
✓Beginners moving up from a starter scope into astrophotography
Look elsewhere if you
!Planetary specialists who need long focal length and aperture
!Deep-sky visual observers chasing faint galaxies
!Buyers who need a complete package, since this is an OTA only
05Build your rig

What to buy next — and where it leads.

7 pieces of gear, ordered by what changes the view most
Recommended upgrades
No fogging on long sessions★ Top pickPegasus Astro Multi-Channel Dew Controller

Keeps the objective dew-free through imaging nights

Make nebulae popOptolong UHC Filter 2″

Boosts nebula contrast for both visual and imaging

Observe all night, no AA batteriesCelestron PowerTank Lithium

Runs a tracker, camera and dew heater away from mains power

Growth path
Better tracking & light imagingSky-Watcher HEQ5 Pro SynScan GoTo Mount✓ Compatible

Commonly paired with this telescope

Portable astrophotographyZWO AM5N Harmonic Equatorial Mount✓ Compatible

Start capturing images of the Moon and planets

A versatile upgradeSky-Watcher Star Adventurer GTi GoTo EQ Mount Kit✓ Compatible

Commonly paired with this telescope

Start imagingZWO ASI2600MC Pro

Start capturing images of the Moon and planets

Lunar & planetary
Excellent contrast
Deep-sky imaging
Strong with a flattener
Deep-sky visual
Wide, low-power views
06The numbers

Full specifications.

6 measured and stated values
Optics
Optical DesignED Doublet Refractor
Aperture73mm
Focal Length430mm
Focal Ratiof/5.9
Mount & drive
Mount TypeNone (OTA only)
Physical
Weight3 kg
07Alternatives

For a different goal, start here.

3 alternatives, each mapped to the goal it wins at
Triplet sibling

William Optics GT71 Triplet APO Refractor

A 71mm triplet with bundled flattener for better color correction

→
Budget option

Sky-Watcher Evostar 72ED

A 72mm ED doublet at a lower price if build matters less

→
Flat-field astrograph

Askar FRA400C Quintuplet APO Refractor

A 72mm quintuplet with a flat field baked in for a step up in imaging

→
Also worth comparing
William Optics RedCat 71 APO
William Optics
William Optics RedCat 71 APO
Closest alternative at this size
Orion SkyQuest XT12 Dobsonian
Orion
Orion SkyQuest XT12 Dobsonian
More capability for deeper views
SVBony SV555 54mm f/4.5 APO
SVBony
SVBony SV555 54mm f/4.5 APO
Smaller and easier to handle