How do you explain this? (Optics)

[asmani]

Hi. As you can see in the video attached, the image of the street is projected on the ceiling! Only a window glass and a simple curtain is involved. How does this happen? And how can I optimize (the window angle curtain etc) to get the most clear picture?

​

 

[Borg]

Your curtains are probably acting as a pinhole camera. The linked article provides the formula for the selection of pinhole size.