What is a Stereoscope?
A stereoscope is a simple tool for stereoscopic observation of a stereo image pair. It is mainly composed of two lenses. The function of the lens is to make the left eye only look at the left photo, and the right eye to look only at the right photo (called phase separation), and enlarge the image. You can see the stereo model by observing the overlapping parts of the two photos through the stereoscope. Stereo mirrors are divided into reflective stereo mirrors and pocket stereo mirrors. The former uses two sets of reflectors that are at an angle of 45 ° to the horizontal plane to expand the eye base distance of the observer to observe large-frame photos; the latter can only be viewed because the distance between the points of the same name must be less than or equal to the eye base distance. Small size photo. The stereo mirror has a simple structure and is easy to carry, and is widely used in aviation geology and photogrammetry.
- A lens is made by grinding a transparent material such as glass into a round thin sheet with both surfaces curved or one surface being flat. Its role is to focus or diverge the light beam by refraction of its two surfaces, and to form an image of the object at any desired location.
- There are many types of lenses, the most commonly used are spherical lenses, that is, lenses formed by two spherical surfaces or one surface being spherical and the other surface being planar. Can be divided into convex lenses and concave lenses.
- A convex lens is also called a positive lens, and its central part is thicker than its edges. According to their cross-sectional shape. It can be divided into three types: biconvex, plano-convex, and moon-convex. Because the convex lens has a converging effect on the light beam, it is also called a converging lens.
- A concave lens is also called a negative lens. Its central part is thinner than the edge part. According to its cross-sectional shape, it can be divided into biconcave, plano-concave or moon-concave. Because a concave lens has a diverging effect on light, it is also called a divergent lens.
- To study the lens, we must first understand the following concepts: (1) The main optical axis. The straight line passing through the centers of the two spherical curvatures of the lens is referred to as the principal axis. (2) Light center. A definite point on the main axis. The direction of the rays of light passing through the lens when they exit the lens is parallel to the direction of the rays of light entering the lens, but there is a side shift. It can be proved that the distance between the center of light of the lens and the center of curvature of its two spheres is proportional to the two radii of curvature. Therefore, only when the radius of curvature is equal, the center of the light and the center of the lens coincide. In general, the position of the center of light is The curvature radius varies, and the optical center is not necessarily inside the lens. (3) Countershaft. That is, in addition to the main axis, the other straight lines passing through the optical center are called auxiliary axes. If the lens thickness is much smaller than the curvature radius of the two spherical surfaces, it is called a thin lens. This entry only discusses thin lenses. (4) Focus. The intersection point of the incident light beams parallel to the main optical axis after being refracted by the lens, or the intersection of the opposite extension lines is called the main focus of the lens, the former is called the real focus, and the latter is called the virtual focus, which is usually represented by F. The focal point in space is called the object-side focal point, which is also called the first focal point, and it is represented by F1; F1 and F2 are separated on both sides of the lens. (5) Focal length. That is, the distance from the center of the thin lens (that is, the optical center) to the focal point. The first focal length is represented by f1, and the second focal length is represented by f2. For thin biconvex or biconcave lenses, f1 = f2, so f is generally used as the focal length. (6) The focal plane is the plane that passes through the main focal point of the lens and is perpendicular to the main optical axis. (7) Sub-focus. That is, light rays parallel to the secondary optical axis that does not have a large angle with the main optical axis are refracted by the lens and converge or diverge. The reverse extension line of light converges to a point on the secondary axis, and the secondary focus is on the focal plane (see Figure 1) ).
- A thin lens can image an object. The distance (object distance) between the object and the lens is different, and the nature of the image (real, virtual, positive, inverted, whether the object is on the same side or different side of the lens, zoom in, zoom out, etc.) different. The image of a known object can be obtained by graphical method and formula method. [3]
- To obtain an image of an object graphically, the light emitted from a point on the object will be condensed to a point after being refracted by a lens, or the reverse extension line of refracted light will be condensed to a point. The set of image points corresponding to each point on the object is the image corresponding to the object. In general drawing, only three special rays (called principal rays) emitted from a certain point on the object are taken, and the convergence point after refraction is the image point (see Figure 2). These 3 special rays are: paraxial rays parallel to the main optical axis, which are refracted by the lens and pass through the second focal point of the convex lens, or look as if they come from the second focal point of the concave lens. Ray 1 in the picture; The light does not change direction, light 2 in the figure; light that passes through the first focus or is directed toward the second focus is refracted parallel to the main axis, light 3 in the figure. Using the method where any two of rays 1, 2, and 3 intersect, once the position of the image point is obtained, the light paths of all other rays from the same object point can be drawn. Ray 4 in the figure.