I was watching this video on the YouTube channel Veritasium. In this episode, the host shows people paper containing holes of different shapes in the middle. So there is a paper which has a hole in the shape of a triangle, another one containing a square, a circle and so on.
Every time you place a cardboard against the sun and observe the shadow, a circle is obtained,at the centre of the shadow, regardless of the shape of the hole. The host explains that this is the image of the sun that we are seeing on the shadow.
I find this difficult to comprehend.
My question is: Aren't 'lenses' required to converge the rays to make an image? How can a hole in the centre of a cardboard form 'images'. When the rays from the sun reach the cardboard they are going to be parallel. How can a hole in the center of a paper form an image from parallel rays? Is the host correct? Is this caused due to diffraction, where in the light bends around the hole, blurring the edges and hence forming a circle regardless of the shape of the hole?
PS: I am sorry, I couldn't summarise the question into a nice title.