I cracked the lens on my FPV camera after a metal pipe jumped in front of my quad...Fortunately, I had another lens from another FPV camera sitting around. But I'm not sure how far away I should be trying to focus this lens. Are there any best practices or rules of thumb to follow?
FPV cameras usually have a large aperture so you should be able to focus it on something over 10 feet away. If you focus it on something too close, It may be blurry when looking at something further away. If that lens doesn't focus, you may need to buy a lens designed for that specific FPV camera.
You can focus the lens by twisting it.