Take a look at your camera, and there’s a good chance it’ll have this symbol: Φ — a small circle bisected by a long line that looks like a hieroglyph of Saturn. If you’ve always wondered what it means, today’s your lucky day: it’s called a “film plane mark” (or “focal plane mark”, depending on who you ask), and indicates exactly where the film (or sensor) plane is inside the camera body. One reason the mark is useful is that macro photographers often want to determine the exact distance between their subject and the film plane, and the mark can make this calculation much easier.

(via PhotoNotes.org via Reddit)

P.S. For a complete list of common camera symbols, check out this page on PhotoNotes.org.

London-based photographer David Wilman recently did some experiments in which he used a Canon 5D Mark II as a digital back for his MPP 4×5 large format camera. He placed his lens-less 5D at the back of the camera at the film plane and then placed a black cloth over the two cameras to prevent any light from spilling onto the sensor. Light from the Schneider Kreuznach Xenar 4.5/150mm lens entered straight into the open mirror box of the DSLR without any physical link between the two cameras. Wilman was surprised to discovered that this pairing produced quite a respectable macro setup.
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