I've been using this for 30 years. It works for helicopters to whatever. Next time your motoring down the highway in your 4-wheeler, roll down your window and look straight down at the road surface. Looks rather blurry eh? Move your vision further ahead until you can focus clearly on the pavement and see the definition of the pavement. The faster you're traveling, the further you will have to look. It appears to me that if your eyes can't focus on the surface because of the apparent speed, you can't accurately judge depth perception. -CY