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title: 'Objects et images in geometrical optics'
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#### course to build

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Important, much confusion possible between point source (real physics, which diffuses the light) or object point (of which, for an optical system, the incident light has the same characteristics ...)

** You have to rewrite everything here, explaining well (parts T, F, M and E). Part F will allow a sufficient synthetic summary. But at least, in this part T, put things right. Of course, it is possible to create sub-chapters, or propose another organization. **


A priori, it will also be necessary to say:

Starting physical objects, extended sources emitting light or scattering incident light in all directions.
These physical sources can be conceived as a set of small elementary surfaces dS emitting or diffusing light in all directions: notion of physical point source.

Characteristic of these point physical sources: all the rays emitted or diffused by a source diverge from the point source. Thus, the light rays associated with a point source converge on this source (here we do not take into account the direction of propagation: on geometric optics, the traced rays are "static".

An optical system modifies the trajectory of the light rays: it is curved (media with gradient of indices) or it is a broken line (change of directions of the rays on the surfaces of the lenses / dioptres / mirrors)

If the rays coming from the same physical point source converge again at a point after crossing an optical system, this new point of convergence is the point image of the point source object by the optical system. the optical system is then said to be stigmatic.

If the light rays at the location of the image are not intercepted by a screen or a sensor, they continue in free rectilinear propagation. If they encounter another optical system during their propagation, from the point of view of the other optical system, the preceding image point appears as the last point of convergence of the light rays coming from the initial physical source: the latter point of convergence defines the point object for the second optical system.

To discern the initial point physical source which is the "point physical object" and diffusing from the start, from the point object that an optical system sees.

A stigmatic optical system couples the notions of "point object" (point position of convergence of the rays incident on the system) and of "point image" (point position of convergence of the rays coming from the point object, after crossing of the system optical).

This point position of convergence of the rays of the object can be "real" ("real object": of the luminous energy is really concentrated in this point) or "apparent" (these are only the lines which carry the light rays which converge, not the physical rays which carry the energy of the light: one speaks then of "virtual object").

Ditto for "image points", they can be real ("real image") or virtual ("virtual image").

A priori in this chapter:
Detailed study of stigmatism, approximate stigma or non-stigmatic of the following simple elements:
- spherical diopter and plane
- spherical mirror and plane
- the reflex reflector? (interesting in itself)
Characteristic in terms of stigmatism (but not detailed study) of the dioptres and parabolic or elliptical mirrors.

part M for reflection: the notion of stigma is linked to the notion of image:
- depends on the "openness" of the optical system (if the image is on a pixel of a sensor)
- also depends on the "openness" of the system observing the image (size of the iris of the eye, or size of the telescope or the lens that reproduce the image). Not clear there, but the idea is simple: a diopter "water / air" plane is stigmatic from the point of view of the human eye. Whatever the position of the eye, he will see a well-defined image. But two human eyes positioned differently will not locate the image at the same point in space. So if the human eye with an iris of much larger size, the image would be fuzzy, and the diopter plane non-stigmatic.