Lens imaging principle and comparison of lenses with different materials


A glass or plastic component used in lamps can change the direction of light or control the distribution of light.

   lens is the most basic optical element that composes the microscope optical system. The objective lens, eyepiece, condenser and other components are composed of single and multiple lenses. According to the difference of its shape, it can be divided into two categories: convex lens (positive lens) and concave lens (negative lens).

   When a beam of light parallel to the main optical axis passes through the convex lens and intersects at a point, this point is called the focal point, and the plane passing through the focal point and perpendicular to the optical axis is called the focal plane. There are two focal points, the focal point in the object space is called the object focal point, and the focal plane there is called the object focal plane; conversely, the focal point in the image space is called the image focal point of the optical lens, and the focal plane there. It is said that after the light from the focal plane of the image side passes through the concave lens, it becomes an erect virtual image, while the convex lens becomes an inverted real image. The real image can be displayed on the screen, but the virtual image cannot.

   Optical glass has high transparency, purity, colorlessness, uniform texture, and good refractive power, so It is the main raw material for lens production. Due to the different chemical composition and refractive index, optical glass has:

  1. Flint glass--Pb oxide is added to the glass composition to increase the refractive index (1.8804);

  2, crown glass-made by adding sodium oxide and calcium oxide to the glass composition to reduce its refractive index (the refractive index of barium crown glass is 1.7055) optical lens;< /p>

  3, lanthanum crown glass-a variety discovered in recent years, it has the excellent characteristics of high refractive index and low dispersion rate, for the creation of The large-aperture advanced lens provides the conditions.


  The main component is organic matter, mainly carbon, hydrogen, nitrogen and oxygen. The resin material used to make the lens must be uniform, transparent and not easily deformed. Currently commonly used types are as follows:

  polymethylmethacrylate (polymethylmethacrylate):

  Trade name: PMMA and Called Alec. The refractive index is 1.49, the dispersion is 58, and the specific gravity is 1.19.

   Advantages: light weight, 1/2 of glass. The focusing lens has good impact resistance and safety.

   Disadvantages: It is a thermoplastic material with a solubility of 75C, and it is easily deformed when heated, resulting in a change in refractive power. The surface hardness is not enough and the wear resistance is poor.

   allyldigluycelcatbonate, also known as allyl glycolic acid ester, trade name: Columbia resin (Colungiaresin, CR-39), which is a petroleum extract . The refractive index is 1.4985, the Abb number is 57.8, and the specific gravity is 1.32.

   Advantages: light weight, safety, good impact resistance, anti-ultraviolet rays, and can block all ultraviolet rays below 350mm. Easy to dye, modern casting mold aspheric lens technology, can be mass produced.

   Disadvantages: poor wear resistance, lower refractive index makes the lens look thicker.

  PC (Polycarbonate), polycarbonate, are polymerized by flexible carbonate aliphatic ring and immobile bisphenol A. The molecular weight is between 20000-38000, and the refractive index is 1.586 under 25C test conditions. Lenses made of this material are called 'space films'.

   Advantages: light, 57% lighter than traditional glass sheets, safe, and its impact resistance is 60 times that of glass, and it can be used as bulletproof glass when the thickness is 2.5cm.

   is thin, the same thickness as the CR-39 lens with a refractive index of 1.6.

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