In Gaussian optics, one can define various types of cardinal points, including the nodal points. By definition, an input ray directed at a nodal point leads to an output ray which has the same direction, only possibly with a parallel offset. For that, an incoming beam from the input side must be directed to the front nodal point, and the corresponding output ray then appears to come from the back nodal point.
In the frequently encountered situation where the refractive index is the same in front of and behind the optical system, the nodal points coincide with the principal points.
Some examples for nodal points:
- The nodal points of a curved interface between two optical media are located at the center of curvature of the surface – possibly far away from the surface.
- For a thin lens, the two nodal points coincide in the center of the length. Therefore, a ray directed to that center will go through the lens without any deflection or parallel offset.
Seealso: cardinal points, Gaussian optics
Questions and Comments from Users
Here you can submit questions and comments. As far as they get accepted by the author, they will appear above this paragraph together with the author’s answer. The author will decide on acceptance based on certain criteria. Essentially, the issue must be of sufficiently broad interest.
Please do not enter personal data here; we would otherwise delete it soon. (See also our privacy declaration.) If you wish to receive personal feedback or consultancy from the author, please contact him e.g. via e-mail.
By submitting the information, you give your consent to the potential publication of your inputs on our website according to our rules. (If you later retract your consent, we will delete those inputs.) As your inputs are first reviewed by the author, they may be published with some delay.