Focusing tips / tutorial: This is how I use the astrophotography Nebulosity 4 software to focus my ZWO ASI1600mm-cool (mono) camera on a star. It helps to pick a bright star as a target. I use my luminance filter while focusing and then leave that focus in place for the rest of the filters (I use a manual focus wheel). I haven't noticed that the other filters need to be re-focused, although many people do adjust the focus for each filter. The Nebulosity software has a 'Fine Focus' feature, but I haven't tried it, I stick a bahtinov mask on the end of my telescope. I use the focus knob on my telescope until 6 perfectly symmetrical diffraction spikes are seen. As I get closer to good focus, other stars will begin to appear. Don't forget to remove the bahtinov mask when you're done focusing.
