A camera obscura is an optical phenomenon made when a pinhole projects the light from outside the room into the room as an image. The image is reversed and inverted, so mirrors can be used to correct it. If you really want to learn about the technology and history of a camera obscura, here’s the Wiki link. But basically, the Giant Camera in San Francisco uses a camera obscura to project an image of the rocks just offshore into the dark room and uses mirrors and a convex canvas to correct the image for you to see.
Adolphe Ganot. Ghost Scenes, Formation of Images in Plane Mirrors, Images of the Camera Obscura, Virtual Image, Decompisition of Light by Prisms, Positives on Glass, Different Kinds of Lenses, Conjugate Focus, Visual Effects of Refraction, Electrical Discharge in Highly Rarefied Gases (Frontispiece). Natural Philosophy for General Readers and Young Persons. 1876.
Our little eclipse buns were super jazzed about using the deluxe camera
obscura I made. I think I used all of the tape. I made the triangular
overhang so I could take pics in there.
One of the pics from the ‘magic box’ where you can see some clouds being
illuminated. We weren’t in the zone of totality. The clouds LOL’d at
us pretty hard and blocked our view at exactly the peak of the eclipse.
Overall, a really neat experience!