William Optics

William Optics ZenithStar 81 APO Doublet

An 81mm FPL-53 doublet apo with William Optics' signature build, clean, colour-controlled stars and a wide flat field with the matched flattener, a beautiful mid-range imaging refractor.

85/ 100

Polaris Score

#5 of 8 imaging APO refractors

See the breakdown ↓

Aperture

81mm

Focal Length

559mm

Focal Ratio

f/6.9

Mount Type

None (OTA only)

Optical Design

ED Doublet Refractor

Weight

3.6 kg

From$1,098

Lowest in 90 days

Price tracked by PolarisObserved 52 timesTracking since Jul 2026

Try in simulator →

Where to buy

Agena AstroProductsPartnerBest price$1,098→High Point Scientific$1,098→

Verified 2h ago · prices tracked daily

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 Double Cluster, side by side.

Two glittering knots of stars sharing one low-power field — a wide, effortless showpiece that rewards the biggest true field you can throw at it.

See Double Cluster through this telescope →

Where else it shines

Within reach

Orion Nebula

Stronger structure — embedded stars plus dark lanes within the core

Open view →

Easy first target

The Pleiades

Many cluster members resolved with color contrast between bright stars

Open view →

Rewards a dark sky

Andromeda Galaxy

Faint elongated smudge — averted vision helps

Open view →

Also excellent on

Saturn

Recognizable disk with subtle markings under steady seeing

Open view →

✦

Tight planetary detail belongs to a longer scope. This one trades reach for a breathtaking field.

01What it's good at

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

Best at

✓An FPL-53 ED doublet controls false colour for clean, largely colour-free stars.

✓81mm and 559mm suit a wide range of large nebulae and galaxy fields.

✓Gorgeous, functional build with a rotating focuser and included rings.

✓Light enough for small trackers, capable enough for serious deep-sky imaging.

Trade-offs

!Needs the matched Flat81 flattener for corner-sharp stars (sold separately).

!A doublet leaves a trace of colour on the very brightest stars versus a triplet.

!OTA only; a tracking mount and camera are extra.

!81mm is a wide-field aperture, not a light bucket for small faint targets.

02In plain English

What These Numbers Mean

Aperture

81 mm

Three and a bit inches of ED glass, about 23 percent more light than a 73 mm. Enough for pleasant lunar and planetary views at moderate power alongside its main job of deep-sky imaging.

Focal length

559 mm

A useful middle field. The Orion Nebula, M31's core and the larger galaxies gain real scale while many of the big nebulae still fit an APS-C sensor.

Focal ratio

f/6.9

Moderate speed. Exposures run longer than a fast astrograph needs, in exchange for gentler tolerances on focus, spacing and tilt. A reducer is the usual upgrade for faster work.

Optical design

ED doublet apochromat

Two elements with ED glass give tight, essentially colour-free stars at this ratio, and the doublet cools quickly and holds alignment indefinitely. Pair it with the matching flattener for round corners.

Weight

3.6 kg tube

About 8 lb, comfortably carried by a small equatorial once a camera and guide scope are attached. Still easy to transport in a single case.

Mount

OTA only

You supply the mount. At 559 mm autoguiding starts to pay off, so favour a mount with a guider port over a bare tracker.

02The Polaris Score

How it scores, and why.

85/ 100

William Optics ZenithStar 81 APO Doublet

#5 of 8 imaging APO refractors

Performance

Ease of use

Portability

Upgrade potential

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.

03Who it's for