Experiences with the ZWO OAG Off Axis Guider

To streamline my equipment, I wanted to move away from the guidescope/guiding camera combo to an off-axis guiding system. I chose the standard ZWO OAG because, together with the ZWO filter drawer, it has exactly the right thickness to ensure a 55mm working distance in front of the sensor of my main camera (ASI2600MC Pro). The components are arranged in the following order:
Telescope – Flattener/Reducer – OAG – Filter Drawer – Main Camera.

I initially used my ASI120MM Mini as my guiding camera, which I had previously successfully used with a William Optics Uniguide 50. With the Uniguide, I usually achieved guiding values ​​of 0.5–1 on my AM3 in good seeing conditions.
It'll be exciting to see what the result will be with the OAG, as one reads and hears very different things...
First, I simply inserted the ASI120MM Mini into the top of the OAG, and when assembling the system, I made sure that the OAG arm was positioned on the long side of the main camera sensor so that it wouldn't be shaded. This is very quick and easy to accomplish thanks to the three possible positions and the included thin spacer rings.

In daylight, I then pointed my telescope at a distant object and first focused the main camera as best as possible using the video function in the ASIair (which I use). The next step was to set the guiding camera as the main camera in the ASIair and also switched to the video function. This allowed me to bring the guiding camera into focus by carefully moving it in its mount. That had to be enough for now. The last thing I did was take a few flats to check if the prism was shading my main sensor. This was also the case with my APSC camera, but was quickly and easily resolved by sliding the arm outward a few millimeters.
At night, I first focused the main camera precisely on the stars and performed the polar alignment. Then I moved the guide camera into focus – I had to adjust the position from the daytime a little. The good thing is that you only have to do this once! From then on, the guide camera is always in focus with the main camera, regardless of what equipment is placed in front of it.
As usual when guiding with the Uniguide scope, I first set my ASI120MM Mini to gain 60 and 1s, and then started the guiding, including calibration, in the ASIair. But then came the disappointment: On my ASKAR 103 with a 700mm focal length at F6.8, guiding stars were only sporadically detected, and the image was generally quite dim. So I increased the gain and also set the aperture to 2s. Now everything worked much better, much better in fact: Despite the small field of view that the 120mm delivers in combination with the OAG and the ASKAR103, the multi-star guiding worked smoothly with dream values ​​around 0.2! A test shot with a 10-minute exposure time had perfectly round stars... So I moved to my subject and started my session with 180s lights. The guiding stayed around 0.2 for hours, at worst 0.4!
WHAT MORE COULD YOU WANT?!
ANSWER:
1. A helical focuser sounds tempting because it allows you to adjust the focus more precisely?! Yes, that may be true – but ultimately, you only adjust everything accurately once and then never again. This way, you can easily reach the focus point manually by moving the camera. Thus, the ZWO OAG is functionally perfectly sufficient as it is.

2. A guiding camera with slightly more sensitivity and a slightly larger field of view, for when the telescope is pointed into areas with few stars. I was subsequently able to work with an ASI220MM Mini, which I found used. With this, I can go to a 1s exposure time with a gain of 250, and there are significantly more stars in the field of view. The guiding values ​​always stayed around 0.2, even with a 1s correction cycle. An absolute recommendation if you're considering purchasing a complete OAG system! But if you already own the small (and rightly popular) ASI120MM, you can certainly use that first.

My conclusion after 5 nights with the OAG: I've never had such good guiding values ​​before, and this is 100% reflected in the roundness of the stars in my light frames. I, for one, would be tired of having to carry an additional guidescope and clearly prefer the OAG instead!

Link to the ZWO Off-Axis Guider for Astrophotography - extensive accessories:

https://www.teleskop-spezialisten.de/shop/Teleskop-Zubehoer/Astro-Fotografie/ZWO-Off-Axis-Guider-fuer-Astrofotografie-umfangreiches-Zubehoer::4311.html