Choosing a guide camera

When you are happy with the guiding on your 500mm rig then there is not much to gain for you and you could check for another ASI120mm in the used equipment marked as a number of people consider upgrading to the ASI220mm or an IR enabled sensor (sony imx662 or others)

When not fully happy with the guiding on your big rig you could consider something like this:

https://www.touptekastro.com/de-eu/products/gpm662m

and an 850nm IR Filter, maybe a 825nm a filter is included, if yes, even better….

The advantage of guiding in IR is that you are less affected by seeing and the finer 2.9um pixels will also be a plus.

When my original Star shoot auto guider camera finally failed, I looked around at what I could replace it with. I chose the ASI290MM Mini for my needs (No longer available new).

My reasoning was simple and based on my guiding experience’s. I wanted a camera with finer pixels for guiding. And I got it.

My aim (no pun intended) is to have the smallest steps available for PHD2 to work with at my 1 second sampling rate. Simply put, finer guiding, finer images.

The theory worked so well that I decided to get a better guide scope and I upgraded from the Orion 50mm, to an Svbony 106 at 60mm. It has worked excellently for me.

Typically, I get a consistent 9 star guiding with PHD2’s multi-star guiding. And my subs show even the finest tiny pinpoint stars. So I’m getting the finest guiding I possibly can.

I tried to do Off-Axis guiding when I started out. Did two months and two different Off-Axis Guiders. Never could get them to work. At the time OAG were for much higher power telescopes like SCG’s. A vender told me I couldn’t use an OAG with my 80mm refractor. So at that point I went to my original Orion 50mm guide scope. Worked the first time, and every time.

But the Svbony is a far superior guide scope. And has a really nice focuser to it.

But I think the more pixels the better,

It’s a Touptek OAG-L. It has a 10×10mm prism

https://www.touptekastro.com/fr/products/oag-l?variant=47631564931384

The 120 has a 4.8 x 3.6 mm sensor, so you are using only 17% of the field of view available with the 120. The 174 is 11.3mm x 7.1mm, so 1.3mm is wasted but you get about 71% of the field of view.

This presumes the prism isn’t masked.

With a wide field telescope a wide field OAG is not really needed (but then neither is an OAG usually), but as the focal length increases, you significantly increase the chance of the OAG landing in a spot with inadequate guide stars.

Eric Gagne · Jan 17, 2026, 09:01 PM

Linwood Ferguson · Jan 17, 2026 at 08:40

With a wide field telescope a wide field OAG is not really needed (but then neither is an OAG usually)

I know….I just happen to like them. It makes extra toys to play with. Guide scopes are too easy 😃

I use the same OAG at 540mm and 1200mm as I did at 2800mm (before I sold the C11 Edge). I like OAG’s also, they solve a lot of issues (flexure being the primary). They cause a few, like needing to stop/start guiding to focus, but I still prefer them.

The SVBony is a good suggestion, unfortunately it’s not stock at my favourite store so this morning I ordered the Touptek GPM662M.

Thank you all for your comments and suggestions