The Nodal Point?
Published : 9th October 2003
What exactly is the nodal point of a lens?
Years ago I was talking to a 1st AC and I think it was mentioned in relation to photographing front/rear projection in a matte painting, where the perspective of the projected component changes during the shot.....my memory is hazy on this, I could be wrong.
The nodal point is very important in VFX. My understanding is that the nodal point is the point behind the lens and in front of the film plane where the image is inverted. Lens >< film This is important for still photography if you are going to stitch to photos side by side together. If you take a bunch of snap shots of a large building the lines will not match. However with the right tripod and camera you can rotate on the nodal point and the lines will match. Another thing you would use this for is those QuickTime panoramas, the ones that you can look around in a circle.
I also understand it is important in cine for matrix like FX's.The apparent travel path needs to be in line with the multiple cameras nodal points.
Multimedia man (looking for work!)
>What about those of us that don't have the American Cinematographer >manual?
Run out and buy one right now. Really. Just got mine in the mail last week and it's well worth it. More content than ever before, organized better than ever before, and the sections I've read make it apparent that the authors have gone out of their way to write in a manner that makes it possible for beginners to get the drift, while still supplying lots of information that you may still need to look up after you've been working for 20 years. This is not easy to do!
Director/DP, Downstream Pictures
The nodal point is the effective optical centre of the lens where all the rays appear to cross. It may be within the lens or in front or behind it, depending upon the construction (normal, telephoto, inverted telephoto.) Another term for nodal point is principal point.
There are actually two nodal or principal points in a lens. The rear one is the point from which the focal length has been determined and the one that is considered the nodal point in this application. (This is contrary to what David Samuelson says in his “Hands-On Manual”, page 99, where he states that we use the front nodal point. I'm not an expert, but Kingslake says it's the rear. This is irrelevant, in any case, because we find the right spot by trial and error, as David outlines).
The important thing is, when the lens rotation is cantered at this point there is no perspective shifting between foreground subject and background image in FP, so the camera/projector alignment remains and no shadow fringing appears around the foreground subject. It is also useful for panning on glass shots, mirror shots, and miniatures, where too much shifting tends to give away the miniature.
Wade K. Ramsey, DP
Dept. of Cinema & Video Production
Bob Jones University
Greenville, SC 29614