This is an apparatus for making transmission holograms of cave formations to capture their beauty in full three dimensional splendor. There are other types of holograms that are easier to make but they do not have as much depth and parallax as the laser transmission type. This is the latest of several cave hologram cameras I have built, each one being lighter, more compact and easier to transport in the rough cave environment.
The device consists of a long coherence length DPSS laser with a shutter mechanism, variable ratio beam splitter, a spatial filter, mirrors to direct the beams and a holder for the holographic plate. The first photograph shows it in a cave set up for a shot.
Since the end product is a transmission hologram, a laser is needed to view it. Fortunately, inexpensive small low power laser are available. My second photograph shows a portable viewer I made from a box disguised as a book. When the book is opened, the hologram lights up. The closer you get to it, the more it seems you're in the real cave.