William Optics RedCat 51 — image 1
William Optics

William Optics RedCat 51

Flat-field 51mm Petzval astrograph, pin-point stars for widefield deep-sky imaging.

93/ 100
Polaris Score
#1 of 12 premium astrophotography scopes
See the breakdown ↓
Aperture
51mm
Focal Length
250mm
Focal Ratio
f/4.9
Mount Type
None (OTA only)
Optical Design
Petzval Refractor
Weight
1.8 kg
From$878

Lowest in 90 daysLowest ever tracked

Price tracked by PolarisObserved 109 timesTracking since Jun 2026

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Where to buy

Verified 13h ago · prices tracked daily

What it's built forOpen these in the simulator →

This telescope was built for the camera.

A fast f/4.9 astrograph designed to throw a wide, flat, well-corrected field onto a sensor. It is an optical tube first — give it a tracking mount and a camera and it rewards long exposures, not eyepieces.

f/4.9 — built to imageNeeds a tracking mount
The view people remember

M57, a perfect smoke ring.

A tiny, flawless grey ring floating in a rich star field — the blown-off shell of a dying star, and one of the most satisfying small targets in the sky.

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

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

Designed specifically for astrophotography with built-in field correction
Best at
✓Designed specifically for astrophotography with built-in field correction
✓Produces sharp, high-quality wide-field images
✓Compact and travel-friendly
✓Minimal setup complexity compared to other imaging scopes
Trade-offs
!Useless for visual astronomy, imaging only
!A quality equatorial mount (significant extra cost)
!Very short focal length, not suitable for planetary targets
!Premium price compared to similar-aperture refractors
02In plain English

What These Numbers Mean

51mm · f/4.9 · 250mm FL
Aperture
51 mm
Two inches of glass, so this is not a telescope for faint or small targets. It exists to deliver an exceptionally clean wide field, and it reaches dim nebulosity through long total integration rather than raw aperture.
Focal length
250 mm
Very wide. The Orion complex end to end, the Cygnus loop and large sweeps of the Milky Way fit in a single frame, which is closer to a fast telephoto lens than a conventional telescope.
Focal ratio
f/4.9
Fast and extremely forgiving. At 250 mm even modest tracking accuracy gives round stars, which is why this is one of the most recommended first astrophotography telescopes.
Optical design
Petzval quadruplet astrograph
A four-element Petzval with the flattener built in, so full-frame corners stay clean with no accessory to buy or space. Its helical focuser and compact body are built around camera use rather than eyepieces.
Weight
~1.6 kg tube
Around 3.5 lb. Any star tracker carries it, and it fits in a camera bag, which makes it realistic to take on a plane for a dark-sky trip.
Mount
OTA only
You supply the mount, and almost anything that tracks will do. This is the cheapest complete imaging setup in the William Optics range once a mount is counted.
03The Polaris Score

How it scores, and why.

93/100 · #1 of 12 premium astrophotography scopes
93/ 100
William Optics RedCat 51
#1 of 12 premium astrophotography scopes
Performance
92
Ease of use
90
Portability
95
Upgrade potential
90

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.

Beginners who want high-quality astrophotography results
Buy it if you
✓Beginners who want high-quality astrophotography results
✓Users building portable imaging rigs
✓Wide-field imaging enthusiasts
Look elsewhere if you
!Budget-conscious beginners
!Visual astronomy users
!Planetary imaging specialists
05Build your rig

What to buy next — and where it leads.

8 pieces of gear, ordered by what changes the view most
Imaging path
Better tracking & light imagingCelestron Advanced VX (AVX) Equatorial Mount✓ Compatible

Commonly paired with this telescope

Portable astrophotographyZWO AM5N Harmonic Equatorial Mount✓ Compatible

Start capturing images of the Moon and planets

Permanent-setup astrophotographySky-Watcher EQ6-R Pro✓ Compatible

Commonly paired with this telescope

Start imagingZWO ASI533MC Pro

Start capturing images of the Moon and planets

Show all compatible mounts (5) →
Accessories
A sharper everyday viewEthos 13mm

Balanced magnification, great for general observing

Wide-field deep-sky imaging
Excellent, flat field
Lunar & planetary
Small image scale
Visual use
Possible, but an imaging tube
06The numbers

Full specifications.

7 measured and stated values
Optics
Optical DesignPetzval Refractor
Aperture51mm
Focal Length250mm
Focal Ratiof/4.9
Mount & drive
Mount TypeNone (OTA only)
Physical
Weight1.8 kg
More
weight lbs3.5lbs
Editor’s Take

The telescope that has probably started more astrophotography journeys than any other premium refractor. It makes beautiful images almost effortlessly, which is why so many experienced imagers still keep one even after buying much larger scopes.

— The Skynocular verdict
07Alternatives

For a different goal, start here.

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

Sky-Watcher Evostar 72ED

Similar concept at a lower price point, good enough for learning

→
more versatile

Celestron EdgeHD 8

Works for both visual and imaging with much more aperture

→
visual + imaging

Celestron NexStar 8SE

If you want to look through it too, not just image

→
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Community

Used in these setups.

Real builds from the community that include this product.

Milky Way Tracker

Featured

The simplest way into tracked astrophotography. A Star Adventurer 2i quietly follows the sky so your exposures stay sharp, while the RedCat 51 frames constellations, the Milky Way core and big nebula regions edge to edge. No laptop, no guiding, no dedicated astro camera — you bring the DSLR or mirrorless body you already shoot with, level it, point it, and shoot.

Beginner Astrophotography Rig

Featured

A forgiving first deep-sky imaging setup. The RedCat 51's short focal length hides the polar-alignment and guiding errors everyone makes early on, and the ASI533MC's square sensor fits its circular field almost exactly — no awkward corners to crop.

08Learn more

Guides and trusted reviews.

2 links — our guides plus reviewers we rate
Guide
Beginner's Guide to Choosing a Telescope
Three clear paths based on what you want to do
Read guide →
Trusted external coverage