Quite a few Xiaomi Yi camera owners are reporting soft or out of focus images. I originally thought mine was close, but after flying with it for a while I wasn’t completely happy with the sharpness. Yeah, it wasn’t close.
There’s a great post at FPV Lab on how to do this. I didn’t have an HDMI cable that fit the camera, so instead of connecting the camera to a monitor, I took a series of still images at various focus settings instead. Once you remove the front face, the camera has a little brass-colored plunger. Pushing that might do something. I’ll let you figure it out.
Taking photos while adjusting the focus worked, but I bet an HDMI output to a monitor would be quicker. Once I found the best focus, I put a few dabs of Goop on the side of the lens to keep it from moving.
Here’s focus setting as I got the camera (white line added for clarity):
I’m not sure if future versions of the Xiaomi Yi will have better focus out of the box. If you have the skills, I highly recommend opening yours up and setting the focus yourself.