A lens is a transparent body that is bounded by two spherical surfaces. The main property of lenses is the ability to give images of objects. They can be imaginary and real, inverted and straight, reduced and enlarged. The linear dimensions of the image vary depending on the location of objects.
Lens magnification - the ratio of the linear dimensions of the image and the subject. The magnification factor (K) can be expressed by the formula: K = u / v, where u is the distance from the lens to the subject, and v is the distance from the lens to the image. The magnification factor is an indicator of how much the linear dimensions of the subject are larger or smaller than the size of the image.
In science, there are such concepts as a collecting lens and a scattering lens. The first is thicker in the middle, and the edge is thinner, the second is the opposite. Lenses are characterized by focal length (from the optical center to the focus: it is negative for the scattering lens and positive for the collecting lens) and the optical power, which is measured in diopters. The focal length of one diopter is 1 meter. The optical power depends on the radii of curvature of the spherical surfaces of the lens, as well as the material (its refractive index) of which it is made. It is the reciprocal of the focal length.
The collecting lens has the following differences from the diffusing:
Gathers the light.
The edges are thinner than the middle.
It is a collection of a large number of triangular prisms expanding towards the middle of the lens (and not toward the edges).
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 extensions.
It is capable of collecting rays incident on the surface at one point, which is located on the other side of the lens.
The collecting lens can be directed to the object on either side, and the rays will be collected in this case, since such a lens has 2 focuses. On the optical axis, the front and rear foci are located on both sides at the focal length from the main points of the lens.
Lens Materials
quartz glass. It is characterized by high heat resistance and throughput of ultraviolet rays. It is also inert to many chemicals;
silicon. This material combines high dispersion with a large absolute value of the refractive index in the infrared range , complete opacity in the visible range of the spectrum;
organic polymers. With the help of casting, it is possible to create inexpensive aspherical lenses, which are used recently more and more often. Soft contact lenses used in ophthalmology are made of biphasic materials. Due to their high oxygen permeability and a combination of hydrophilic properties, silicone-hydrolium lenses can be continuously used for a month;
other materials.
Types of Lenses
Collecting lenses are divided into 3 types:
biconvex;
flat convex;
concave-convex.
Scattering lenses are also divided into 3 types:
biconcave;
flat concave;
convex-concave.
Lenses can be simple, or can be combined from several - to build some kind of complex optical systems. A system of lenses located at a certain distance, whose axes coincide, is called centered.
Lens application
They are necessary for the manufacture of telescopes, microscopes, binoculars, cameras, projectors, optical sights , etc. Lenses are also actively used in ophthalmology, since they are necessary for people with visual impairments such as myopia and hyperopia. In addition, a single collecting lens is used as a magnifying glass.