When doing astrophotography, you need to focus on dim things in the dark, and in my case, with old eyes. So you really need some kind of aid to get the super sharp focus you need for the task.
Fortunately there is what’s called a Bahtinov mask. Basically a grating you put over the end of your telescope or DSLR lens that causes a diffraction pattern that makes it easy to see when a star is in focus.
Here is a video I put together that shows the steps to design, convert to a 3D model and slice a Bahtinov mask for a DSLR lens.
Wikipedia page describing Bahtinov masks
Stefanos's Blog 