Just under a decade ago we moved to the west coast of the US and lived near San Francisco. Being new to the area we wanted to see as much of the area as possible and one sunny day, when checking out the ruins of the Sutro Baths and nearby Cliff House, we stumbled across this wonderful camera obscura on the cliff edge:
This camera obscura (literally “dark room”) uses a mirror in the pointed roof of the building to reflect light down through a lens onto a 6 ft (2m) diameter parabolic horizontal viewing table which gives a more even focus across the surface, magnifying the image 7-fold. What makes this one even more interesting is that the mirror rotates a full circle every 6 minutes giving a full 360° view of the area.
This wonderful building was built in the late 1940s as part of the Playland amusement park and was only placed on the National Register of Historic Places in 2001 after several threats of demolition following the closure and redevelopment of Playland in the 1970s.
The images of Seal Rock and the surrounding area were amazing, especially when considering this is such relatively simple technology, first described in the writings of the Chinese philosopher Mozi in the 4th century BCE.
Even the children were impressed back then, and that takes a lot to achieve these days!