What focal length and guiding scale does the 50 mm guide scope give?

The one I link to is 180 mm at about f/3.6 (180 mm over 50 mm). With the ZWO ASI120MM Mini's 3.75 micron pixels that is about 4.3 arcseconds per pixel (206.265 x 3.75 / 180).

Which camera did I guide with?

An ASI120MM mono guide camera, on my RedCat 51 rig with the ASI533MM Pro and a 7x2 inch ZWO filter wheel.

What mount carried that rig?

The TeSeek 11. The whole rig, guide scope included, weighed 4.11 kg.

What have I not tested on the 50 mm guide scope?

I have not weighed this guide scope on its own or measured its guiding error apart from the whole rig.

Generic 50mm guide scope review: guiding my RedCat 51 rig

Where does it rank on our leaderboard

Nine of the 46 accessories on my board, against price
Rank	Accessory	Stars for Your Buck	Recorded UK price
1	GEMINI EAF	100 out of 100	£42
2	Generic Dew Heater	93 out of 100	£9
4	Telescope Cover	90 out of 100	£25
6	Generic Guide Scope 50mm	88 out of 100	£41
21	365 Telescope Cover	74 out of 100	£209
33	ZWO EAF	51 out of 100	£199
44	Unihedron SQM-L Sky Quality Meter with Lens	32 out of 100	£149
45	SKY ROVER 2x54 Binoculars	28 out of 100	£139
46	365 Solar Telescope Cover	5 out of 100	£73

Contents

01 Where does it rank on our leaderboard
02 Specifications and features
03 In use
04 In my words
05 Watch it in my videos
06 Should you buy it?
07 Questions and more about this review

In 30 seconds

Stars for Your Buck 88/100

Reviewed 30 Aug 2025 Updated 25 Sep 2026

Rank: #6 of 46 accessories
Verdict: Damon's pick

Written by Damon Scotting 2 min read

Buy it if

You want a standard 50 mm guide scope for a small or medium refractor
You guide with a small mono camera such as the ZWO ASI120MM Mini
You want a helical focuser rather than a plain sliding drawtube

Skip it if

Your mount is close to its payload limit: a 30 mm mini guide scope is lighter
You want a published weight and back focus: this listing states neither

The 50 mm guide scope is the one I paired with an ASI120MM guide camera on my RedCat 51 narrowband rig. The one I link to is EYSDON's 50 mm: a 180 mm focal length scope with a helical focuser and a 1.25 inch port.

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Specifications and features

Generic Guide Scope 50mm reviewed #6 of 46
Recorded UK price	£41
Aperture	50 mm
Focal length	180 mm
Focal ratio	f/3.6
Focuser	Helical, with a quick-focus drawtube
Camera connection	1.25 inch, T2 external thread
Length	218 to 240 mm
Mounting	Two rings 90 mm apart on a foot 31 mm wide
Coating	Fully coated
Linked model	EYSDON 50 mm guide scope

In use

On my RedCat 51 narrowband rig

On the TeSeek 11, the Moon behind

Mine, on camera

In my words

“I could have made the payload of this setup a lot less, particularly by replacing the huge filter wheel, guide scope, and swapping for a non-cooled IMX 533 sensor camera like the Player One Saturn camera, and an SVBONY filter drawer.”

From my TeSeek 11 mount video review

Watch it in my videos

I tried a £299 Telescope mount?! Surprisingly GOOD! (TeSeek 11 mount) · published 30 August 2025 · 8:14 · Watch on YouTube · 24,851 views, 861 likes on 2 Oct 2026

Jump to

2:34 GOAT setup
3:00 The rig: RedCat 51, 50 mm guide scope and ASI120MM
3:33 Guiding results
6:46 Improvements

Should you buy it?

88/100 Stars for Your Buck

Pros

50 mm of aperture at 180 mm focal length, by the listing
A helical focuser with a quick-focus drawtube, and a 1.25 inch port with a T2 external thread
Two rings 90 mm apart on a foot 31 mm wide
It guided my RedCat 51 narrowband rig with an ASI120MM guide camera

Cons

The listing states no weight and no back focus
On a small mount it is one of the parts I would swap to cut the payload
At 180 mm the guiding scale is about 4.3 arcseconds per pixel with the ASI120MM Mini: fine for short refractors, coarse for long focal lengths

The 50 mm guide scope has guided my RedCat 51 narrowband rig with an ASI120MM guide camera: a simple, light way to guide a small refractor.

Three alternatives

Questions and more about this review

Reviewed by

Damon Scotting

The Telescope Man Verified

BSc (Hons) Physics with Astrophysics and Cosmology, Loughborough University PGCE / QTS, University of Nottingham

About Damon About Damon Damon Scotting is The Telescope Man. He holds a BSc (Hons) in Physics with Astrophysics and Cosmology from Loughborough University and a PGCE with QTS from the University of Nottingham, and taught physics in secondary schools before becoming an astronomy creator. He is a contributing writer for BBC Sky at Night Magazine and the author of 42 Wonders of Our Night Sky, and his photograph of the galaxy M100 with the dwarf planet Ceres was Highly Commended in the Astronomy Photographer of the Year 2024 competition run by Royal Observatory Greenwich. He has appeared on the BBC's Blue Peter. More than 750,000 people follow his astronomy channels on YouTube, Instagram and TikTok, and he has reviewed more than 140 telescopes, mounts, cameras, filters and accessories hands-on for this site. More about Damon · How I test · Damon's book

I review all kinds of gear: most of it I buy, some is gifted and some is loaned, and all of it is reviewed the same way. How this site is funded

Four questions, answered

Questions about the Generic Guide Scope 50mm

Reviewed 30 August 2025 ·Updated 25 September 2026

I review all kinds of gear. Most of it I buy, some is gifted and some is loaned, and all of it is reviewed the same way: no company sees or approves a review before it is published. Shop links marked Ad are affiliate links: I earn a commission when you buy through them, at no extra cost to you. How this site is funded

What focal length and guiding scale does the 50 mm guide scope give? The one I link to is 180 mm at about f/3.6 (180 mm over 50 mm). With the ZWO ASI120MM Mini's 3.75 micron pixels that is about 4.3 arcseconds per pixel (206.265 x 3.75 / 180). The specifications ↓
Which camera did I guide with? An ASI120MM mono guide camera, on my RedCat 51 rig with the ASI533MM Pro and a 7x2 inch ZWO filter wheel. In use ↓
What mount carried that rig? The TeSeek 11. The whole rig, guide scope included, weighed 4.11 kg. Watch it in my videos ↓
What have I not tested on the 50 mm guide scope? I have not weighed this guide scope on its own or measured its guiding error apart from the whole rig.