In a digital world obsessed with snapping billions of images with compact cameras and cell phones, a camera that’s totally mechanical and as big as a SmartCar is a rare find.

The 30-year-old Polaroid Land 20x24 is such a camera. A giant relative of the handheld Polaroid Land instant cameras, it commits 20-by-24-inch images to large sheets of photo paper. One of four working models in the world lives in Tribeca, at John Reuter’s 20x24 Studio in a loft on Murray Street.

Though familiar with these machines, I had not seen one in person until I was asked to have my portrait taken for a series titled “Behind Photographs.”

Tim Mantoani, a master portrait photographer based in San Diego, is using Polaroid 20x24 to capture noted photographers holding prints of their favorite shots. I brought my photo of Nelson Mandela being released from prison in South Africa in 1990.

“A lot of people know these images but have no idea who the people are behind these photographs,” Mantoani said. “[It’s] important for future generations to understand...that the photographs come from people, not from cameras.”

A day after my portrait session, I returned to watch Tim work.

Operating the wood-encased camera’s brass gears, levers and giant red bellows was Jennifer Trausch, the studio’s director of photography.

Trausch loads the rolls of film and paper, and the chemical pods that go between them. She helps Tim set up the shot by adjusting the bellows and the ground glass back. When the shutter is released, she pulls the paper down with a string. After two minutes, the material is separated to reveal the final image.

John Reuter says they have enough film for the next four years. He doesn’t know whether another manufacturer will come along to supply new stock.

As one who remembers, as a kid in the ’50s, the wonder of first seeing instant pictures from my parents’ Land camera, I really hope so.