A real image that is inverted and reduced is a camera.
A real image is formed by the intersection of actual rays of light, and an imaginary image is formed by the intersection of the reverse extension of actual rays of light. A real image is one that can be picked up or recorded on a light screen or white paper or film, and an imaginary image is one that cannot be picked up on a light screen or white paper or recorded on film. An inverted image is always a real image, and an orthogonal image is always an imaginary image. If the image and the object are on opposite sides of the lens, it is a real image, and if the image and the object are on the same side of the lens, it is an imaginary image.
1, real image. Light rays from an object reflected or refracted by an optical system (such as concave mirrors, convex lenses, lenses), re-convergence and resulting in a picture similar to the original (magnified or reduced). Real image by the actual light convergence can be shown on the screen, can make the negative feel, so called real image.
2, virtual image. Like a collection of points is called the object of the image, if the beam is diffuse, then the diffuse beam of the reverse extension of the intersection of the line called the virtual image, that is: the virtual image of the reflected light or refracted light by the reverse extension of the line of convergence, can not be shown on the screen.
Relation between focal length and image distance:
When the object distance is greater than 2 times the focal length, the image distance is between 1 times the focal length and 2 times the focal length, into an inverted, reduced image. At this time, the image distance is smaller than the object distance, the image is smaller than the object, the object image opposite side. When the object distance is equal to 2 times the focal length, the image distance is also at 2 times the focal length, forming an inverted, equal-sized solid image. In this case, the object distance is equal to the image distance, the image and the object are equal in size, and the image is anisotropic.
In physics, the object distance is the distance from the object to the center of the lens. The physical symbol for the object distance is u, the unit is the international unit of length m m. For the lens, through the center of light and perpendicular to the optical axis of the plane, that is, the object side of the main plane is also the image side of the main plane overlap. Object distance and image distance exist *** conjugate relationship, the more distant the object distance, the closer the image distance; on the contrary, the closer the object distance, the more distant the image distance.
In optical calculations, strictly speaking, the object distance should be the distance between the subject plane and the main plane in front of the lens. When the object distance is less than 2 times the focal length, greater than 1 times the focal length, the image distance is greater than 2 times the focal length, into an inverted, magnified solid image. At this time the image distance is greater than the object distance, the image is larger than the object, the image is located on the opposite side of the object. When the object distance is equal to 1 times the focal length, there is no image, and parallel light is emitted. When the object distance is less than 1 times the focal length, it is an orthogonal, magnified virtual image. At this time, the image distance is greater than the object distance, the image is larger than the object, the image of the same side.