Went out on a rare clear night to a wetlands near me to take some photos of the stars. As it was so dark, and the stars are so small, I had to rely on the focus peaking function of my camera to tell if the stars were in focus or not.
I’ve got home and started to process the photos, and I’ve found out that despite the camera telling me that they were in focus, they clearly weren’t.
Hey ho, what’s a wasted few hours in the freezing cold between friends…
Your camera’s focus most likely looks for hard contrast vertical lines in your picture then racks the focus through its range and looks for the sharpest transition between those contrast lines. In this picture you can see that all the vertical lines have very high and sharp contrast.