To achieve stable image processing, it is essential to choose the most suitable lens for the application based on knowledge of the characteristics of the lens. There are many different types of lenses, each of which offers different effects and are classified according to their shape and material characteristics. This article introduces the history of lenses from their early days to the present day.

Creation of concave and convex lenses

Lens – Lens comes from the Latin name “Lentil”, which originated in the Mediterranean region. This is an example of an imported word called ‘tokyo (transparent mirror)’ by Japan during World War II. Its origin can be traced back to crystal or glass balls used as fire-starting tools in religious ceremonies or as accessories in ancient civilizations. It is generally accepted that the origin of lenses can be traced back to the ancient Roman philosopher Seneca, who described how “letters can be magnified with a crystal ball” about 2,000 years ago.

Lenses work on a principle known as “refraction” of light: light bends and changes its direction of travel. Convex lenses are spherical in shape with a thicker center that converges light rays; while concave lenses, which are now glass with a thicker periphery, diverge light rays.

Mechanism of refraction and function of concave and convex lenses

Uses of Concave and Convex Lenses

Lens have been developed in two areas: the eyeglasses we wear every day in life and instrumental applications such as lenses used in microscopes, telescopes and cameras. The first eyeglasses put into practical use in the 13th century were actually reading glasses (simple magnifying glasses) using convex lenses. It was originally called the “Devil’s Tool”. Later, 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?

The correct answer is the microscope, which was invented in the late 16th century. Later, an Englishman, Hooke, developed a compound microscope using two convex lenses (objective and ocular), and at about the same time, a single-lens microscope was first developed in the Netherlands. The telescope was invented by a Dutchman, Lippershey, who used a convex lens as the objective and a concave lens as the ocular. It was Galileo who immediately perfected this invention and used it for astronomical observations; he was able to use this device to discover the rings of Saturn. In addition, a German astronomer, Kepler, invented the Keplerian telescope using a convex lens as the objective and ocular.

How Myopic Eyeglasses and Concave Lenses Work

Mechanism of presbyopia (farsightedness) and eyeglasses with convex lenses

Types of Lenses

Concave and convex lenses are divided into different types including: spherical lenses which have a circular surface, aspherical lenses which have a curved surface rather than being spherical, cylindrical lenses which have a concave surface, toric lenses which are shaped like a part of a doughnut and Fresnel lenses which have a surface similar to a washboard. In these lenses, light is refracted on the lens surface. Although there are other types of lenses including GRIN lenses (gradient index lenses) which produce optical effects by providing a gradual change in the refractive index of the lens material rather than by refraction on the lens surface or diffractive lenses which use the phenomenon of spreading of light waves. GRIN lenses are commonly used for endoscopes and diffractive lenses for CD and DVD players.

Lenses use surface refraction	Spherical Lens
	Aspherical Lens
	Cylindrical Lens
	Toroidal Lens
	Fresnel Lens

Lenses use a mechanism other than surface refraction	GRIN lens (gradient index lens)
	Diffraction lens

 

Types of Lens Shapes

All the lenses shown below use the phenomenon of refraction on the lens surface.

Thay đổi vật liệu ống kính: từ Thủy tinh sang Nhựa

Thấu kính và pha lê thuở ban đầu là những mặt hàng xa xỉ không dễ kiếm được. Việc sản xuất thấu kính thủy tinh bắt đầu tăng lên do sự cải tiến của kỹ thuật chế tạo thủy tinh vào thế kỷ 12; sau đó vào thế kỷ 19 thấu kính thủy tinh quang học có độ trong suốt cao được phát minh. Ống kính quang học đóng vai trò quan trọng trong thế kỷ 20, và hiện nay có hơn 200 loại ống kính. Chúng có thể được chia thành hai loại: loại thủy tinh crao (có khả năng tán sắc thấp) có chỉ số khúc xạ thấp chứa vôi soda và loại thủy tinh flin có chỉ số khúc xạ cao hơn chứa chì. Thấu kính quang học bằng nhựa xuất hiện vào đầu thế kỷ 20, nhưng tốc độ truyền ánh sáng và chỉ số khúc xạ thấp trên các mẫu đầu tiên. Nó lan truyền nhanh chóng sau khi nhựa nhiệt rắn được phát triển vào những năm 1940. Sau sự phát triển mới này, thấu kính nhựa nhiệt dẻo được chế tạo để có độ trong suốt ngang với thủy tinh quang học, nhưng chỉ nặng bằng một nửa. Ống kính nhựa này đã góp phần vào sự phát triển của kính áp tròng và máy ảnh lấy liền vì nó dễ đúc, khó vỡ và chế tạo không tốn kém. Gần đây những thấu kính này đã được sử dụng trong kính đeo mắt và máy ảnh điện thoại di động. Các vật liệu thấu kính khác bao gồm thạch anh, fluorit, gốm sứ trong suốt quang học, halit trong suốt hồng ngoại, silicones và germani.

Thấu kính quang học (kính Crown, kính Flint)

	Refractive Index	Abbe Index (Dispersion)	Material Properties
Glass crao	Small	Large (Small)	Hard and light
Flin glasses	Large	Small Large)	Soft and heavy

Changing 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 several optical elements is called a “compound lens”. After 1839, when the first silver halogen camera, a daguerreotype, was invented, compound lens technology improved greatly, spurring the development of new types of lenses. These included the Davidson type, in which two meniscus lenses were symmetrically placed, the Petzval type, which shortened the shooting time, the Triplet type, with three detachable lenses that succeeded the Petzval type, the Tessar type, and the Sonnar type. In the 20th century, the zoom lens was invented. The advent of the zoom lens, which could change the focal length in a single lens, marked a breakthrough in the development of high-performance lenses. These lenses covered a wide field of view using standard, wide-angle and telephoto focal lengths as well as high magnification. Later, many variations were developed as magnification capabilities, weight reduction and size reduction were further improved. The lens world also entered a period of systematization.

Mechanism of different camera lenses and zoom lenses

Latest Lens Technology

Lens are used in virtually every electronic device: for example, collimating lenses in CD-ROM drives that read red LED laser beams, scanning lenses in laser printers, and lenses in optical lenses used for barcode readers and endoscopes. Another example is the projection lens of an advanced step (Step and Repeated Projection Exposure System) that enables processing of semiconductors at the micron scale, which is a precision lens made of layers of top-quality glass silica. It is known as the “king of lenses”.

In short, one might ask, “What is the best camera lens in human history?” The answer is “the human eye (crystal lens)”, which can freely adjust its thickness to achieve the appropriate focal length. In fact, the most modern lens, modeled after a crystal lens, is currently under development. It is called a liquid lens. This lens is made from two types of liquids with different conductivity, insulation properties and refractive indices that can freely change the focal length by adjusting the thickness and shape of the lens using the surface tension effect. Since it does not require a focusing mechanism or actuator, it is expected to be used in a wide range of applications across a range of industries from consumer electronics and medical devices to the security field.

Mechanism of liquid lens technology