What's the Φ mean?

Anyone know what the Φ-symbol means that appears on most (at least 350D, 20D & 1D) bodies?

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It's indication of sensor (or film on film cameras) plane. I think distance on lens is distance from subject to sensor plane.

I think that mark shows the sensor/film location for people who measure distance to calculate exposure factors for close-ups. It's not as important today as it was when we only had film.

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Well - you learn something new everyday!
Thanks tiha!

[I]I saw this being used to set up the camera on a pano tripod head. They said it was needed to keep everything on the same axis when panning and stitching photos together. Called the nodal point. Correct me if I am wrong here.

If I remember right, the nodal point will be found somewhere in the middle of the lens. If you rotate the cam around it, you won't see parallax on distant subjects. Do a forum search for pano to maybe find some more info.

They were wrong if they called it the nodal point, as the nodal point is a characteristic of the lens. It's the optical center of the lens relative to either the subject (first or front nodal point) or the film plane (second, or rear, nodal point). They may have a table of nodal point distances and be using that (the sensor plane) to precisely locate the nodal point. It's an easy enough matter to explain fuzzily, but a little less intuitive to explain clearly.

Hey Photosguy - that's a wicked F setup in your image! Is that the 105/2.5 P Nikkor attached? That's the stuff I grew up on.

So why isn't the film/sensor plane marker not important anymore just because we went digital?

Always nice to meet another Nikon guy! Yes, its the 105 which I'm sure that some people aren't too happy to hear, still rates higher that most "L" lenses!

What I said was, "It's not as important today as it was when we only had film." Big difference, no?
Not as important since we have the histogram, or can pop the card into the computer & check out what's going on in the shot.

PhotosGuy wrote:
Always nice to meet another Nikon guy! Yes, its the 105 which I'm sure that some people aren't too happy to hear, still rates higher that most "L" lenses!

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What I said was, "It's not as important today as it was when we only had film." Big difference, no?
[B]Not as important since we have the histogram, or can pop the card into the computer & check out what's going on in the shot.

And what does the histogram have to do with the camera focal plane? Not trying to be argumentative here. Just trying to get a little more enlightened since I've always known what that mark on the camera was, even during my film days, but I personally never had to use it myself. But I figured there must be a practical use for it, othewise why would camera makers bother including it on the body. Very tight close-up work would be one practical use. But I can't see how using a sensor vs film would make any difference as far as using the marker to measure distance from subject to the camera focal plane is concerned.

Nothing!

The mark is really intended to accurately measure the amount of lens extension you're using when using extension tubes and bellows, so that you can look up the amount of exposure compensation needed to make allowance for light fall-off (due to the extension), or to accurately measure film plane to subject distance. There are exposure compensation tables available which tell you the amount of compensation required for a given amount of lens extension.

If you're more mathematically inclined you can work out the exposure compensation yourself using the Inverse Square Law ...

http://csep10.phys.utk​.edu …lect/light/inte​nsity.html

Correct it is the exact position of the recording medium film/sensor, used mainly, as also mentioned for extreme close up shots where DOF is measured in millimeters...

Focal plane.

PacAce wrote:
So why isn't the film/sensor plane marker not important anymore just because we went digital?

'In the old days' if you shot macro work and wanted precise reproduction of sizes, you wanted to know exactly where the film was. Given the fact that digital sensors are all over the place in terms of precise size and given the fact that inkject printers are 1200 or 1440 dpi basic resolution, getting a 1:2 exact reproduction seems to be less an issue of how big the image is 'on the negative', and more a question of the output magnification and image sizing in your output software! But the digital world macro consideration is speculation on my part, since I don't try to shoot true macro and have accurately scaled prints.