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# Collecting lens

The lens is a transparent body, which is bounded by twospherical surfaces. The main property of lenses is the ability to give images of objects. They can be imaginary and valid, inverted and straight, reduced and enlarged. Linear dimensions of the image vary depending on the location of objects.

Lens magnification - ratio of linear dimensionsimage and subject. The magnification factor (K) can be expressed by the formula: K = u / v, where u is the distance from the lens to the object, and v is the distance from the lens to the image. The magnification factor is an indication of how much the linear dimensions of an object are greater or smaller than the image dimensions.

In science there are such concepts as collectinglens and scattering. The first is thicker in the middle, and the edge is thinner, the second is all the way around. Lenses are characterized by a focal length (from the optical center to the focus: in the scattering lens it is negative, and in the collecting lens - positive) and the optical power, which is measured in diopters. The focal length of one diopter is 1 meter. The optical force depends on the radii of curvature of the spherical surfaces of the lens, as well as the material (the index of its refraction) from which it is made. It is the reciprocal of the focal length.

The collecting lens has the following differences from the scattering lens:

1. Gathers the light.

2. The edges are thinner than the middle.

3. It is a collection of a large number of triangular prisms expanding toward the middle of the lens (and not to the edges).

4. The focus of the lens (that is, the point of intersection of the rays after refraction, located on the main optical axis) is real (and not imaginary), since the rays themselves intersect, and not their continuations.

5. Capable of collecting beams incident on the surface at one point, which is located on the other side of the lens.

6. The collecting lens can be directed to the objecteither side, and the rays will be collected, since such a lens has 2 foci. On the optical axis, the anterior and posterior foci are located on both sides at a focal length from the main points of the lens.

Materials for lenses

• quartz glass. It is characterized by high heat resistance and throughput of ultraviolet rays. It is also inert to a variety of chemical reagents;

• silicon. This material combines a high dispersion with a large absolute value of the refractive index in the infrared range, full opacity in the visible range of the spectrum;

• organic polymers. With the help of casting, it is possible to create inexpensive aspherical lenses, which have been used more frequently lately. Soft contact lenses used in ophthalmology are made from materials that are biphasic in nature. Silicone-hydrolium lenses due to high oxygen permeability and a combination of hydrophilic properties can be continuously used for a month;

• other materials.

Types of lenses

Collecting lenses are divided into 3 types:

• biconvex;

• plane-convex;

• concave-convex.

Dispersing lenses are also divided into 3 types:

• biconcave;

• flat-concave;

• convex-concave.

Lenses can be simple, and cancombined from several - to build some complex optical systems. A system of lenses located at some distance, whose axes coincide, are called centered.

Application of lenses

They are necessary for the manufacture of telescopes,microscopes, binoculars, cameras, projectors, optical sights, etc. Lenses are also actively used in ophthalmology, since it is necessary for people who have such shortcomings as nearsightedness and farsightedness. In addition, a single collecting lens is used as a magnifying glass.

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