Sky-Watcher EvoGuide 50DX APO Guide Scope — image 1
Sky-Watcher

Sky-Watcher EvoGuide 50DX APO Guide Scope

50 mm f/4.8 apochromatic refractor

A small, high-quality telescope that rides piggyback on your main scope and keeps your photos sharp during long exposures. It's good enough to take pictures through, too.

86/ 100
Polaris Score
Our pick when a guide scope should pull double duty
From$375
Where to buy
Affiliate link — we earn a commission, you pay the same. We rank on fit, not payout.
What problem does this solve?

A cheap guide scope guides. This one guides and shoots.

Photographing galaxies and nebulae means holding the shutter open for minutes at a time. Even a good motorized (equatorial) mount drifts a few arcseconds every minute, and that tiny drift smears every star into a streak. A guide scope fixes it: a small telescope that rides piggyback on top of your main scope, watches a single star, and feeds constant tiny corrections back to the mount so your stars stay pinpoint.

Yes, it looks like a chunky finderscope, and it mounts the same way, up on top of the main scope. The difference is what goes in the back: not your eye, but a small camera (more on that just below). This one is also apochromatic, or “APO” for short — premium glass that keeps stars a clean white instead of ringing them with a purple halo. That quality is why it doubles as a tiny camera lens for the sky: point a camera through it and you can photograph a big target like the North America Nebula in a single shot.

You need one if
You need one if you photograph the deep sky on a motorized (tracking) mount and want long exposures to come out sharp — with the bonus of a tiny wide-field telescope you can shoot through.
You can skip it if
You can skip it if you only take short snapshots, stick to the Moon and planets (which don't need guiding), or a basic mini guide scope already keeps your stars round.
How it actually works

What the setup looks like.

The guide scope itself has no electronics — it's just glass and a tube. It becomes a “guiding” system once you add two inexpensive pieces. Here's the whole chain:

The guide scope itself has no electronics — it's just glass and a tube. It becomes a “guiding” system once you add two inexpensive pieces. Here's the whole chain:

1
Mount it on your telescope
It clamps on top of your main scope, in a finder shoe or on a spare dovetail rail. Nothing plugs into the scope itself.
2
Screw a guide camera into the back
A small, cheap camera (like a ZWO ASI120MM Mini) threads into the focuser where an eyepiece would normally go. This is the “eye” that watches the star.
3
Free software locks onto a star
A program called PHD2, running on your laptop, picks one star in the camera's view and measures any drift several times a minute.
4
It nudges the mount
PHD2 sends tiny correction signals to your mount through a cable, canceling the drift so your main camera's long exposure stays razor-sharp.

You can also bolt a DSLR or mirrorless camera to the back and shoot wide-field photos directly through it (it takes standard T-ring adapters). What you don't do is look through it by eye — it's built for cameras, not eyepieces.

01Will it fit my setup

Compatibility.

What this accessory works with — check the fit before you check the price.

What this accessory works with — check the fit before you check the price.

Any main telescope (refractor or reflector)Finder shoe or dovetail railZWO / QHY / Player One guide camerasPHD2 & similar free guiding softwareDSLR / mirrorless (via T-ring)Motorized equatorial mounts
Note✕Needs a small guide camera (sold separately)✕Only helps on a motorized tracking mount✕Heavier than a basic mini guide scope
02The numbers

What These Numbers Mean

4 numbers in plain English · full specifications

4 numbers in plain English · full specifications

Focal lengthGuiding
242 mm
Long enough to give a guide camera real resolution on a guide star and short enough to find one almost anywhere in the sky. That combination is what makes a dedicated guide scope more reliable than a short finder-guider.
ApertureSensitive
50 mm ED
Fifty millimetres of ED glass reaches faint enough stars that you rarely have to hunt for a target, and the ED element keeps stars tight so the guiding software can centroid them accurately.
Focal ratioFast
f/4.8
Fast optics mean short guide exposures, typically one to two seconds, which lets the mount respond to errors quickly rather than chasing them after the fact.
FlexureCritical
Rigid rings and dovetail
Any flex between guide scope and main telescope shows up as drift the software cannot see and cannot correct. Solid mounting hardware matters more here than optical quality, which is why the ring and bar design is part of the product rather than an afterthought.
Optical
Aperture50 mm
Focal length242 mm
Focal ratiof/4.8
LensAir-spaced ED doublet (apochromatic)
Physical
FocuserHelical (twist-to-focus), holds position
Camera threadM42×0.75 (standard T-thread)
MountingTube rings + dovetail + finder stalk
Weight~0.9 kg (under 2 lb)
03Before you buy

Good to know.

The honest caveats — the things that save you a return, a bad first night, or a second purchase you didn't need.

The honest caveats — the things that save you a return, a bad first night, or a second purchase you didn't need.

It's a real telescope, not just a pointer.
The apochromatic (APO) lens is sharp enough to photograph through. On a small camera it frames big objects — the Pleiades, the Andromeda core, the North America Nebula — beautifully.
You still need a small camera.
It's sold separately and does the actual watching. A basic mono guide camera is inexpensive and threads straight into the back.
You focus it by twisting the barrel.
There's no focus knob — you rotate the front of the tube, then it holds position all night. Great for set-and-forget guiding; takes a couple of tries to nail for photos.
Editor’s Take

If your guide scope will only ever guide, a basic mini scope does the job for a fraction of the price. The EvoGuide 50DX is for the imager who wants one more small telescope in the bargain: it keeps your exposures pinpoint, then turns around and photographs the wide-field targets a big scope can't fit. You pay more than a plain guider, and it earns it the first clear night you point a camera through it.

— The Skynocular verdict
86/ 100
Sky-Watcher EvoGuide 50DX APO Guide Scope
50 mm f/4.8 apochromatic refractor · $375

A small, high-quality telescope that rides piggyback on your main scope and keeps your photos sharp during long exposures. It's good enough to take pictures through, too.