Nodal points
Two points on the lens axis where a ray of light enters and leaves. The front point is where image distance is measured from and the rear one is where the focal length is measured from.
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Nodal points
Techniques Glossary Nodal points
Two points on the lens axis where a ray of light enters and leaves. The front point is where image distance is measured from and the rear one is where the focal length is measured from.
Nodal points are located in two areas in a compound lens system. The front nodal point is where rays of light entering the lens appear to aim. The rear nodal point is where the rays of light appear to have come from, after passing through the lens.
Most normal lenses have nodal points located roughly in the center of the lens, near the shutter. In contrast, the optical center of a telephoto is located in front of the lens.
Of course, you can set up a scene and find and mark the nodal points of all your lenses in one fell swoop; then when you're setting up a panorama, the mounting process will be much faster.
There are a number of methods of finding the nodal points of a lens, but none are simple. I won't discuss them here. Instead I'll describe a couple of methods of measuring focal length.
Their rear nodal points are so close to the sensor that they have red-tinged left sides and blue-tinged right sides. It's nasty. They work great on film, but forget it with the M9, at least if you care about quality.
The Warp filter lets you create distortion by moving nodal points on a grid pattern. A range of 'artistic' effects is available.
 See also: Light, Lens, Nodal point, Image, Camera
  
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