how does this work?
In: Physics
Have you ever been in a room with a bunch of canned lights for illumination. You have a whole bunch of different shadows from each light source that darken where they over lap.
Now imagine a room with a ceiling filled with canned lights. You probably wouldn’t cast much of a shadow at all because every part of you and the ground would be lit by enough lights that your shadow would be very indistinct multiple lights.
If you make a camera obscura from a box without closing the end it doesn’t focus an image, because light from every visible object is projected across the entire space, just like you didn’t cast a shadow in the room filled with light sources.
If you extinguish all but one of the canned lights, you’ll have a very distinct shadow with crisp edges because now there’s only one light source so when you block it, there’s very little light reaching the area your shadow covers.
A pinhole makes all the light come from one tiny point, so all the light reaching any part of the screen is only coming from one part of the scene. Just like your shadow would be sharp in a large room illuminated by one small light source, the each part of the screen is illuminated by the light from only one object so it projects a sharp image.
A lens uses optical trickery to allow the size of the pinhole to grow, while the light from one part of the scene is focused to a single virtual point.
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