REVIEW:
ZWO ASI 120MM Mini

First published November 2021
Last updated January 2026

Contents Featherweight guidecam Functionality Any downsides? Where to buy

Intro

For many years I used the ZWO ASI 120MM Mini as my primary guide camera. It’s small, lightweight, and widely used in astrophotography guiding setups. In this review, I share my long-term experience with the ASI 120MM Mini, looking at its strengths, limitations, and how it performs as part of a practical guiding workflow.

Featherweight guidecam

These guidecams are common sights on imaging rigs, and it’s easy to understand why. First off, they’re cheap, selling around the £140 mark. They’re also diddy, measuring 61mm from bow to stern (not including any adapters). Perhaps best of all, they’re light, coming in at a featherweight 240g. Keeping the overall weight of your system down is generally a good thing to do, so this gets a tick from me for sure.

They’re also easy to use. There’s a USB2.0 Type C port on that back, used for connecting to whatever system you’re using to control the camera. I use an ASIAIR Plus and it works perfectly, no fuss or drama.

Important note! ZWO used to make non-mini versions of this guidecam, the ASI120MM and ASI120MC. They’ve been discontinued now but second-hand ones still occasionally crop up for sale. Those versions aren’t compatible with ASIAIR controllers. I almost bought one by accident….

Functionality

Also on the back is an ST4 port. This can be used to connect the ASI 120MM mini to the mount that you’re using. However, if you’re using an ASIAIR, I have good news: all functionality is provided via the USB cable, and the ST4 port is unnecessary. Happy days!

Onto the sensor. Noise levels are fairly low, or at least low enough that images are clean enough for effective guiding. The sensor itself is fairly small, just 1/3″. This is fine though if you’re using the camera for its intended purpose, i.e. guiding.

You want a wide field of view to ensure you can see multiple stars — multi-star guiding is standard now with the ASIAIR PRO and Plus — so I recommend using the ASI 120MM Mini with a guidescope that has a suitably low focal length. I originally used mine with a William Optics 32mm Slide-base Uniguide Scope, which was an excellent match for my Askar FRA400 telescope, with its wide focal length of 400mm. I then upgraded to an Askar 130PHQ, which has a much longer focal length of 1000mm. To make the most of the guidecam, I switched to a larger guidescope: a William Optics 50mm with ROTO Lock.

Any downsides?

So, what’s the downside? There are two I can think of, but they’ll only crop up if you push the camera beyond its intended use. First, with a resolution of 1280×960 and the ability to capture at 35fps, in principle this little camera could also be used for planetary imaging. However, that small sensor and the slower USB2.0 connection will hold you back. If you want to do planetary imaging, best to get something designed with that in mind.

Second, a guidecam with a smaller pixel size would offer a higher level of precision. But to be honest if you’re using a wide-field telescope for your imaging like I am, the ASI120MM mini is easily sufficient.

So there you have it. Simple, easy, cheap, works well. Thanks, ZWO!