I am using this camera with a small 50mm Orion guide scope (only 162mm focal length). Even with such a small scope, this is guiding my 6" Celestron scope on an AVX mount with excellent tracking. Any tracking errors are much smaller than any disturbances caused by seeing conditions so stars remain sharp on my DSLR even with 3 minute exposures (I could go as long as I want, but 3 mins is a suitable cutoff time for me). Sensitivity with this setup is amazing even with short (less than a second) exposures and never fails to find stars wherever I point the scope.

I have used one of these cameras as a guide camera and it is fine for this purpose. However I needed a low light sensitive camera to monitor the position of the scopes within the dome to ensure the aperture tracking was accurate. The ASI120 with a ZWO wide angle lens fitted running through SharpCap produces a crisp, zoomable image in near darkness, which can now be monitored remotely, given it is PC based. I notice ZWO now include right angled USB plugs, which put less strain on the connector. Thoroughly recommended.

Great Service from FLO as usual and this camera works a treat when combined with my WO Guide scope. Connected to the ASIAIR plus (also ordered and fast delivery from FLO) via my ZWO 2600MC Pro on the USB2 Guide port, I’ve managed to focus and get star sizes right down. Sure there is the more sensitive guide camera but it’s almost double the price - there’s really no need for the more sensitive version IMO as the 120 does a great job with a guide scope. Maybe I’ll get the more sensitive version if I go down the OAG route but I’d be using that with a longer focal length OTA than I currently have… Recommended for quality and service !

I have recently started astrophotography and initially I was taking photos without guiding and wasn’t able to get above 40 second subs but with the guide camera, PHD and sharp cap my polar alignment is way better and I can now usually get around 5 minute exposures before trailing.

Having not had a chance to use this outside, I've only been able to set this up on the kitchen table to ensure it connects, which it does. It's fits very nicely into the William Optics 32mm Guide Scope https://www.firstlightoptics.com/guide-cameras/william-optics-32mm-slide-base-uniguide-scope.html . I'll update more as and when I'm able to test the tracking with PHD 2.
But, all in all, this seems like a well made piece of kit, worth the money. Recommended.

Perfect for what I need. It's solid, sensitive and as light as a feather. Thanks again to Chris for his help and expertise.

Bought this to replace another camera which although worked well it just wasn't sensitive enough for guiding with, with 120mm I can get a few stars to lock on to so its worth it's weight in gold to me

Purchased things after many reviews online and the 120mm is everything you want. Quality product, easy to set up and easy to use. The service and delivery time from First Light Optics was its usual high standard.

Arrived the day after ordering - FLO really excelled this time. I was a bit unsure how to set the camera up in INDI since my imaging camera is from ZWO too, but once I'd figured it out, it has worked flawlessly. But most importantly, the images produced are really low noise and it makes for a great guiding camera - PHD2 can pick out multiple stars for the multi-star guiding and I'm getting sub-arc second guiding on my AZ-EQ5GT / SharpStar 15028HNT on the first night out after just a quick calibration. I'll probably look to replace the guide camera on my obsy's EQ6R-Pro with an ASI120MM in the future. The only thing that would improve this camera would be the inclusion of a 1 1/4" parafocal ring so that you keep focus more easily after removing the camera for whatever reason, so I'll be getting one when they are back in stock.

Great guide cam. It's simple and effective! It pairs well with my WO 32mm Uniguide scope.

Achieving focus is easy and can be done using the camera's native app. For first time use, I focused it during the day while holding the guide scope in my hand and read the graduated index on my guide scope. Using that as a beginning point, I was able to fine-tune the focus while mounted during the night. Now for daily use, I have the final reading on the guide scope, so I can quickly set it up.

Application support is great. Besides PHD2, I also use it with SharpCap Pro for polar alignment.

Service from FLO and their delivery partner was amazing. Ordered from India, and received on the 4th day!