SPENCER COX, PETAPIXEL:
It might seem like one of the simplest parts of photography: leveling your horizon. Most photographers want their horizons to be straight, of course, but this isn’t an area of photography that gets too much attention. And why would it? Leveling the horizon is a very easy task — right? In practice, though, it requires more care than many people think.
You can’t just rely on your camera’s “virtual horizon,” or your post-processing software’s “auto straighten” tool. Our perception of a level horizon is more complicated than that.
Read more, here.