[https://www.youtube.com/watch?v=a0H0vOWUjbY](https://www.youtube.com/watch?v=a0H0vOWUjbY)
Was recently watching the new Allen Pan video on making a laser grid lawn mower, and I was just confused by why we can see the lasers on the video, when it seems him and his friends couldn’t. At 6:45 it seems clear that Backyard Scientist uses his camera to see the lasers themselves because they wouldn’t be visible unless they shined the light into their eyes, but the camera can pick up the path of the lasers?
In: Physics
You can only see the paths of a beam of light because the beam is reflecting off particles in the air or being scattered by the medium itself. Unless you were really, really careful about the space you were in, you’re always going to get some of that scattering. Cameras can pick up even the very faint scattering with a long enough exposure because they’re effectively integrating the light hitting the sensors over time, but human eyes are more dynamic and relative and don’t pick up really faint light easily while adjusted for brighter light (such as looking at where the beam is reflecting off something)
I don’t know anything about Allen Pan’s video production, but I’m quite sure he’s using a cinematography tool called a Hazer that…. adds haze to an environment to make things like light beams (and lasers) more visible. You can actually see the haze in his garage in the shot at 1:33 before he turns the laser on.
Conversely, here’s a short clip I recorded this past weekend of my CO2 laser using my phone camera. As you can tell, you can’t see the laser at all. You can barely see it interacting with the material.
[https://imgur.com/a/02iIznK](https://imgur.com/a/02iIznK)
The light is scattering off of particles of dust and other stuff in the air. Only a small fraction is getting scattered but it’s enough to make the beam visible (especially once things start smoking).
The guys in the video can’t see it very well because they’re wearing goggles that are designed to block most of the light at that wavelength. You don’t want even a small accidental reflection to get in your eye with the amount of power.
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