This video is one by Veritasium on Poisson's Spot.
In the later half of the video where he does the experiment by using a laser, why does the laser beam have to pass through a diverging lens. Is it mandatory for it to pass through a diverging lens and why?
Also, if it is mandatory to use a diverging lens, are there any common household items that can be used instead of a specialized diverging lens? For the demonstration, would a circular coin also work or does the object have to be a sphere?