The best place to observe these things is in a mirror. You will be able to see any point around you at a specific place on the mirror by positioning yourself properly. This means that there are at least some rays from every point in space reaching the selected point on the mirror from where you are able to see that point in space.
I performed a series of experiments to understand focus and the behavior of light, which I will unravel here:
SECTION1: The green light source was placed at a certain distance from the match stick. Even though the match stick had completely blocked the 2D space or projection of the light source which was an led, it is completely recovered when the focus point is shifted from the match stick to the led.
From the perspective of our eye or the camera, the light source forms a 3D cone; the apex of which is at the source itself and the base at the lens or our eye. This is the reason you see a larger circle patch of green light when the match stick is focused, which is at a distance from the led. It is like truncating the 3D cone at a particular distance from its apex. Depending on at what distance from the apex you are truncating you will be getting circles of different diameters. Larger the diameter lesser will be the intensity of the light, because the energy has now spread out.
If you take the focus point to the surface of the lens, you will see that the diameter of the circle will be the same as the diameter of the aperture of the lens.
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