History of Machine Vision : Lens

Uses of Concave and Convex Lenses

The lens has been evolving through two fields: the eyeglasses we wear daily in our lives, and tool applications such as lenses used for microscopes, telescopes, and cameras. The first eyeglasses, put into practical use in the 13th Century, were actually a reading glass (simple magnifier) using the convex lens. In the beginning, it was called the “devil’s tool”. Meanwhile, eyeglasses with two lenses appeared, and eyeglasses for myopia (nearsightedness) using concave lenses were invented in the 16th Century.

Which was invented first, the microscope or the telescope?

正确的答案是显微镜，它是在16世纪末发明的。随后，英国人胡克（Hooke）使用两个凸透镜（客观镜头和眼镜）开发了一个化合物显微镜，并且在几乎同一时期，荷兰首次开发了单个晶状体显微镜。望远镜是由荷兰人Lippershey发明的，Lippershey将凸镜用作客观镜头和凹面镜头作为眼镜。正是伽利略立即完善了本发明并将其用于天文观察。他能够使用该设备发现土星环。此外，德国天文学家开普勒设计了开普勒望远镜，该望远镜将凸透镜既是客观镜片又设计。

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镜头类型

The concave and convex lenses are subdivided into many different types including: the spherical lens with a rounded surface, aspherical lens with curved surface profiles that are not spherical, cylindrical lens with a hogbacked profile, a toroidal lens that is shaped like a part of a donut, and the Fresnel lens with a washboard-like surface. On these lenses the light is refracted on the surface of the lens. While there are other types of lenses including the GRIN lens (gradient index lens) that produces optical effects by providing a gradual variation of the refraction index to the lens material and not by refraction on the lens surface or the diffractive lens that utilizes the phenomenon of the spreading out the light waves. The GRIN lens is often used for endoscopies and the diffractive lens for CD and DVD players.

镜头形状的类型

All lenses shown below utilize refraction on the lens surface.

镜头材料的更改：从玻璃到塑料

早期的眼镜和水晶是奢侈品,我们re not easy to obtain. The production of glass lenses started to increase due to the improvement of glass-making techniques in the 12th Century; then in the 19th Century the high transparency optical glass lens was invented. The optical lens played the key role in the 20th Century, and now there are over 200 types of them. They can be roughly divided into two types: the crown glass type with low refraction index which contains soda lime and the flint glass type with a higher refraction index which contains lead. The optical plastic lens appeared in the early 20th Century, but the light transmission rate and refraction index were low on the early models. It spread rapidly after thermosetting plastic was developed in the 1940s. Following this new development, thermoplastic lenses were made to have transparency comparable to optical glass, but only weighed half as much. This plastic lens contributed to the development of contact lenses and instant cameras because it is easy to mold, hard to break, and inexpensive to make. Recently these lenses have been used in eyeglasses and cell phone cameras. Other lens materials include quartz, fluorite, optically transparent ceramics, infrared-transparent halite, silicones and germanium.

光学镜头（皇冠玻璃，火石玻璃）

Change in Camera Lenses: from Single Focus to Zoom

When a lens consists of a single optical element, it is called a “simple lens”; a lens made up of a number of optical elements is called a “compound lens”. After 1839 when the first silver halide camera, a daguerreotype, was invented, the compound lens technology improved tremendously, spurring the development of new types of lenses. These lens types include the Davidson type in which two joined meniscus lenses were placed symmetrically, the Petzval type which shortened the time required for photographing, the Triplet type with three separable lenses that succeeded the Petzval type, the Tessar type and the Sonnar type. In the 20th Century, the zoom lens was invented. The arrival of the zoom lens that can change focal lengths within one lens marked a breakthrough in the development of high performance lenses. These lenses cover a wide field of view using standard, wide angle, and telephoto focal lengths as well as high magnification. Subsequently, many types of variants were developed due to further enhanced magnification, weight reduction, and downsizing. The lens world has also entered a period of systemization.

最新的镜头技术

镜头几乎用于每个电子设备：例如，读取红色LED激光束，激光打印机中的扫描镜头的CD-ROM驱动器中的准直镜，以及用于条形码读取器的光纤范围中的镜头和内窥镜。另一个例子是启用Micron量表的半导体加工的尖端步进器（步进投影曝光系统）的投影镜头是由高品质玻璃体二氧化硅制成的精确镜头。它被称为“镜头之王”。

In summary, one might ask, “What is the best camera lens in human history?” The answer is “a human eye (crystalline lens)”, which freely adjusts its thickness to gain an appropriate focal length. In fact, the state-of-the-art lens, modeled on the crystalline lens, is now under development. It is called a liquid lens. This lens made from two kinds of fluid of different conductivity, insulation property, and refraction index can freely change the focal length by adjusting the thickness and form of the lens using surface tension effects. Since it requires neither a focusing mechanism nor a drive unit, it is expected to be used in an array of applications through a wide range of industries from home electronics and medical equipment to the security field.