Godfrey
somewhat colored
OK, as an Engineer you've confuse me. A reference point is only useful as a point to take a measurement from. So maybe we are saying the same thing. The film plane mark is a reference mark to a measurement from (to the lens mounting flange), which for a Nikon is 46.5 mm as described in the Nikon manual. Then again maybe it's maybe it's because it's after midnight and I've had two dirty martinis -
Enjoy your martinis and think about it in the morning.
The focal plane reference mark allows you to make any number of measurements, including that of the lens mount register. It simply indicates where the focal plane is and does not constitute a measurement in and of itself.
... just like the Plimsoll mark on a ship's hull. It's a reference mark to say "don't let the freeboard be less than this." From it, you can measure the ship's draft with a given load ... those are measurements from the reference mark.
G
farlymac
PF McFarland
Relevant or not, the symbol is the Greek letter Phi, equivalent to our letter F, which stands for Film...
Being a Navy vet, I prefer the Plimsol mark reference. Phi is 90° out of register.
PF
css9450
Veteran
I noticed my old Nicca/Tower camera uses the symbol, and my Canon IIf has a dot.... The Leotax cameras use the symbol too. Looks like most of the Japanese cameras used an indication of some kind, but we still don't know who used it first.