Easy Focusing With Astro Cameras

I don't know you, but I struggle with the lack of real-time feedback when focusing on my ASI camera. Particularly with my SCT telescope with its long focus travel.
I also use the telescope in many different configurations (for observing, for shooting at the Moon with a mirrorless or planets with my astro camera. And even to photograph DSO using the Celestron focal reducer).
So here is a neat tip I got from a chap following my same Facebook group about astrophotography: use a parfocal ring and an eyepiece.