Traditional Culture Encyclopedia - Photography major - What materials are the lenses of Sony and Canon SLR? Is it resin lens or resin with optical glass lens? Hope to seek truth from facts!
What materials are the lenses of Sony and Canon SLR? Is it resin lens or resin with optical glass lens? Hope to seek truth from facts!
Of course, the possibility of resin lenses is not ruled out, but most of them appear in cheap lenses.
Below, the commonly used lens of Canon lens is described:
fluorite
The fluorite lens with very low refractive index and low dispersion not only has excellent infrared and ultraviolet transmittance, but also can better remove the chromatic aberration that affects the definition of the shot picture.
Canon's technical strength: play the specialty of fluorite on the lens.
Fluorite (crystal) with almost no color difference
Processing technology of fluorite lens
Fluorite/ultra-low dispersion lens and ordinary lens
compare
Fluorite is a magical stone, which can glow at high temperature. Because of its beautiful color like fireflies flying in summer nights, it is named "fluorite". Fluorite is formed by crystallization of calcium fluoride (CaF2). Its remarkable characteristics are extremely low refractive index and dispersion, and good transmittance for infrared and ultraviolet rays. However, it is worth noting that it also has bright and delicate depiction performance that ordinary optical glass can't achieve. Because the focus deviation caused by light passing through the general lens will lead to color divergence and reduce the clarity of the captured image, we call it chromatic aberration. Fluorite lens has little dispersion and almost no chromatic aberration, so it is the most suitable lens for photography. However, there is almost no fluorite as big as that used in SLR camera lenses in nature, so it can be said that it is a long-standing wish for people to make artificial fluorite lenses.
Canon developed the artificial crystallization technology of fluorite in the late 1960s, and adopted fluorite lenses in the series of white lenses and ultra-telephoto L lenses. Only Canon has used fluorite in the lens of SLR cameras, which is highly appreciated by photographers all over the world because of its delicate description and high contrast.
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The length of the telephoto lens can be shortened.
Because it is difficult for ordinary optical lens to compensate the bending aberration of the picture, it is impossible to shorten the length of telephoto lens. Using fluorite lens with low refraction can greatly shorten the length of telephoto lens while maintaining high image quality.
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List of fluorite lenses
Telezoom lens
EF 70-200mm f/2.8L IS II USM
Ef 70-200mm f/4L is USM.
Ef 70-200mm f/4L USM
EF 100-400mm f/4.5-5.6L is USM.
Telephoto fixed-focus lens
EF 200mm mm f/2L is USM.
EF 300mm f/2.8L is USM.
Super telephoto fixed focus lens
EF 400mm f/2.8L is USM.
EF 400mm f/4 DO is USM
Ef500mf/4l is USM.
EF 600mm f/4L is USM.
EF 800mm f/5.6L is USM.
Super UD lens
UD (Ultra Low Dispersion = Ultra Low Dispersion) lens developed by Canon is an optical lens with low refraction and low dispersion. Two UD lenses can obtain almost the same high-performance optical characteristics as fluorite lenses.
In order to make more lenses obtain ideal chromatic aberration compensation
5 UD lens is EF 70-200mm f/2.8L IS II USM.
Although fluorite has ideal color difference compensation, it is difficult to use large fluorite lenses on many lenses because of its high cost. Therefore, by using two UD lenses, the elimination effect of secondary spectrum is improved, and the performance is almost comparable to that of fluorite lens with excellent color difference compensation performance, which has been used in various lenses.
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Super UD lens with further improved optical performance
After developing UD lens, Canon made persistent efforts to develop "super UD lens", which greatly improved the optical performance of UD lens in 1993. It further contributes to the high performance and miniaturization of the lens, and is widely used in various lenses such as standard, telephoto and ultra telephoto.
Grinding aspheric lens/aspheric lens
Spherical aberration compensation of large aperture lens, image distortion compensation of wide-angle lens and miniaturization of zoom lens-aspherical lens is one of the indispensable technologies to solve these three problems.
Beyond the excellent expressive force of spherical lens
Image distortion
When representing the subject, the spherical lens will appear various "distortion" phenomena.
The lens of a SLR camera usually consists of several spherical lenses. However, no matter how advanced the technology is, in theory, spherical lenses can't focus parallel rays on one point in a complete shape, so there must be some limitations in image expressiveness. In order to solve the three difficult problems of spherical aberration compensation of large aperture lens, image distortion compensation of ultra-wide angle lens and miniaturization of zoom lens, Canon began to develop aspheric lens technology in the mid-1960s, and determined the design concept and precision machining and precision detection technology. 197 1 year, the world's first aspherical lens for SLR cameras was successfully commercialized.
Example of image distortion of super wide-angle lens
The picture on the left is a photo taken by a lens without compensation function, with barrel distortion. The picture on the right shows the photo taken by the lens with compensation function.
Spherical aberration of spherical lens (left) and focal consistency obtained by aspherical lens (right)
Aspheric lens can achieve 1 point parallel focusing that spherical lens can't.
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An aspherical lens called an "ideal lens"
In the past, it was extremely difficult to manufacture aspherical lenses and accurately test their shapes. It was considered a "dream" to manufacture aspherical lenses. Without the technical development of Canon, there would be no compact lens with high performance and expressive force today.
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Unique grinding technology and batch production and processing technology.
Precision aspheric lens
Canon adopted a unique batch production and processing technology when producing aspherical lenses, and the grinding accuracy reached 0.02 micron. 1978 also realized the production of small-aperture aspheric lenses molded by high-precision plastics. Subsequently, a large-aperture glass molded aspheric lens was introduced, which can be applied to the lens of SLR cameras at low cost. In addition, the technology of replicating aspheric surface is established to form ultraviolet curing resin film on the surface of spherical lens. And in the development and design stage of EF lens, according to various lens types, appropriate aspheric technology is adopted.
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An aspheric lens is very effective for shooting scenes with many point light sources.
When shooting scenes with many point light sources, such as city street night scenes, the spherical lens is affected by spherical aberration, resulting in spot bleeding (see the right). If it is an aspherical lens, even the point light source around the picture can be photographed clearly and beautifully (see the left picture).
A photograph taken by an aspherical lens.
Make a shot
Achieve high image quality and miniaturization comparable to ultra-high performance EF lens-"L lens". The charm of DO lens (multilayer diffractive optical lens) lies in its sharp and clear expressive force and the flexibility brought by exquisite body.
Solve various problems such as color difference.
DO lens (multilayer diffractive optical lens)
If the refractive index of light passing through the lens changes, it will lead to color bleeding (color difference), which will lead to the decline of image quality. In order to compensate it, it is necessary to combine multiple convex mirrors and concave mirror to offset it. Therefore, the original telephoto lens and zoom lens need to use multiple lenses, resulting in a large lens volume. Canon took the lead in developing "DO (Diffractive Optics) lens" for cameras, which successfully solved these problems.
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Realize miniaturization and lightweight of telephoto lens.
If the number of lenses used increases, the volume and weight of the lenses will increase. This not only increases the difficulty of shooting, but also causes hand shaking. Compared with the volume and weight of a fixed-focus lens designed with only refractive optical elements, the volume and weight of the lens using DO lens are only about 2/3 of the former.
Miniaturization and lightweight of DO lens fixed focus lens
Compared with 400mm f/4 lens, a compact lens with a total length of 84.3 mm and a weight of 920 g is realized by equipped with DO lens.
Lightweight.
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Color difference compensation principle of DO lens
Diffractive optical elements and refractive optical elements have completely opposite properties in color difference. DO lens makes use of these properties to realize zero chromatic aberration lens in theory. The double-layer DO lens independently developed by Canon adopts a laminated structure, and the diffraction gratings precisely fabricated on the surface of the glass lens are close to each other with micron accuracy. * Micron (micron): 65,438+0 micron equals 65,438+65,438+0 million meters.
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DO lens further evolved into a three-layer structure.
Double-layer structure DO lens cross section
Cross section of DO lens with three-layer structure
With the continuous research on the materials, shapes and structures of diffractive optical elements, Canon has successfully developed a three-layer DO lens which is composed of three diffractive optical elements. There is no longer unnecessary refracted light in the incident light, and the light can be almost completely used for shooting, thus realizing the miniaturization of the telephoto zoom lens.
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Lens list with DO lens
Telezoom lens
EF 70-300mm f/4.5-5.6 DO is USM.
Super telephoto fixed focus lens
EF 400mm f/4 DO is USM
Subwavelength structural coating
Solve various problems such as color difference.
This is a new coating technology, which uses a principle different from ordinary steam coating to prevent light reflection. The phenomenon of light reflection on the lens surface is caused by the sudden change of refractive index at the boundary between lens glass and air. Reflection will produce glare and ghost, which will affect the image quality. In order to suppress light reflection, the refractive index between air and glass should be gradually reduced. If there is a coating that can change the refractive index smoothly between air and glass, the light entering the lens will not be reflected too much from air to glass or from glass to air. This is the antireflection principle of subwavelength structured coating (SWC). As early as the 1960s, it was found that moth's eyes can effectively inhibit light reflection, because the uneven microscopic surface of its eyes can act as a low refractive index coating.
Sub-wavelength structured coating (SWC) forms a wedge-shaped microstructure on the lens surface, which is shorter than the wavelength of visible light. This structure can continuously change the refractive index, thus eliminating the boundary where the refractive index will suddenly change, and achieving better reflection suppression effect than evaporation. Evaporation is a thin film formed on the lens surface that is less than the wavelength of visible light, which can inhibit the reflection of light, but its effect will weaken with the increase of incident angle of light. However, sub-wavelength structural coating (SWC) has excellent antireflection effect even when the incident angle of light is large.
Canon took the lead in using sub-wavelength structural coating (SWC) technology on EF 24mm f/ 1.4L II USM. This innovative technology is of great value to lenses, especially wide-angle lenses, in suppressing ghosts and glare.
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