God's Palette

The sharp point produced by the light rays passing through the lens and brought to the image sensor is called focus.If the shot is blurry, it is called out of focus.Focusing the lens can be done by autofocus or manual focus.

[-]. Lens mount

The device that combines the lens with the body is called a mount.All digital SLR cameras use the bayonet mount system, and the lens can be easily and quickly attached to or detached from the body.Usually lenses of different mount systems cannot be used interchangeably.For example, Nikon lenses cannot be mounted on Canon bodies. The 4/3 system is an exception.

[-]. Minimum focusing distance

The shortest distance from the subject at which the lens can focus clearly is called the minimum focus distance.This distance is calculated from the front group elements of the lens.Different lenses have different minimum focusing distances, ranging from centimeters to several meters.Short focal length lenses usually have a closer minimum focusing distance than long focal length lenses.

[-]. Fixed focus lens

A prime lens has a fixed focal length, say 28mm, 50mm or 135mm, etc.The counterpart of "fixed focus" is "zoom".

[-]. Standard lens

A standard lens refers to a lens with a focal length or angle of view that is almost equal to the field of view of the human eye, which is about a 50mm focal length.A small zoom ratio lens covering a focal length of 50mm can be called a standard zoom lens.

[-]. Telephoto lens

Technically speaking, a lens with a narrower angle of view than the human eye is called a telephoto lens, which means that any lens over 50mm is a telephoto lens, but we usually think of longer, more effective lenses, such as 200 Lenses with 300mm, 400mm, and [-]mm focal lengths are common telephoto lenses.

Thirteen, wide-angle lens

The human eye has an angle of view of about 46 degrees; wide-angle lenses have a greater angle of view than that, and typically they have a focal length of 35 mm or less and have an angle of view between 60 and 108 degrees.

③ Some lens structures

Tessar was invented by Zeiss optical designer Paul Rudolph in 1902, but to understand Tessar, one has to start with its environment. In fact, Galileo knew how to build astronomical telescope lenses before the invention of photography. But these lenses have a small angle of view, and high-quality lenses with large image fields were a big challenge in the 19th century (all were calculated and manufactured manually, and the raw material processing technology was poor).

Almost in 1812, the British scientist Wollaston discovered that if the concave surface of a crescent-shaped convex lens faces outward, and an aperture is added in front of the lens, the viewing angle can reach about 40 degrees, which is slightly smaller than the equivalent full-frame 50mm, and the effect is It is better than using a convex lens on the front, especially at the edge of the image.From today's point of view, the aperture of this lens is about F14. At that time, the spherical aberration and coma aberration were not large, and the image was flat, which also slightly reduced the distortion.

But it is a real 1 piece 1 group design.The most important thing is that in 1837, the French art master/chemist Daguerreotype invented the first camera in history, the Daguerreotype. During the original exploration period, the lens was originally very simple and compact.

But although the lens structure is very simple, F14 is still a bit unbearable, so the Petzval structure was born in 1840, which can achieve a super large aperture of 8mm F10 level on the 250 X 3 large-format camera, and the Petzval structure is actually nothing more than a 4 pieces in 3 groups, 2-1-1 design, the front is convex-concave bonding to correct spherical aberration and partial coma, and the rear is concave-convex separation to correct residual coma. The characteristic of the Petzval structure is that the image field is not flat, and it is also the originator of the very famous "vortex blur out of focus".

The initial equivalent full-frame focal length is about 85mm, and the aperture is large enough, so it is also called "Petzval portrait lens". Although it needs to use a metal lens barrel in the large-format era, it is bulky and basically only suitable for indoor use. But back to the structure, 4 pieces and 3 groups are obviously not complicated at all.

However, it is not difficult to see that the Petzval structure solves the problem of aperture, but does not solve the problem of wide angle. Therefore, in the 1860s, a new symmetrical design structure Rapid Rectilinear with concave-convex/convex-convex 4 pieces and 2 groups was born, which can achieve 50 degrees (equivalent to full The angle of view of the frame is about 45mm), and the aperture is between F6~F8. This structure was very successful in the early days of photographic equipment and has been used for nearly 70 years. But from the perspective of our God, such parameters are obviously antique-level, and for The main ones are large and medium format, simple in structure but bulky in size. With the continuous popularization of photography in the field of news, newer and smaller designs will inevitably appear, such as the Triplet in the early 20th century.

Triplet is designed for 3 pieces and 3 groups. The convex and concave are not bonded. The concave mirror is made of lead oxide, and the convex mirror is made of silicic acid. These are some materials that are not mainstream now or are not allowed to be used because of environmental protection. But at that time However, its performance is quite outstanding. Cook Optics Co., Ltd., which invented this structure, is still in production today, and it is also an old-timer in the optical circle.

There are 2 lenses with the most classic triplet structure, which are from Dongcai commonly known by netizens, Triotar 1950mm F135 launched by Carl Zeiss Jena in the 4s, and Elmar 90mm F4 (1931-1968), the longest-selling lens in Leica history. The second version of the lens, which was launched around 1964, used a triplet structure of 3 elements and 3 groups.Although the structure is very simple, the lenses at that time were almost made of metal materials, and the thickness of the glass was generally not low, but even so, the weight of the Carl Zeiss Jena Triotar 135mm F4 was only 450 grams, and the weight of the Leica Elmar 90mm F4 It is less than 300 grams. It can be said that the beginning of the Triplet era has basically seen the signs of modern miniaturized lenses.

The word Tessar comes from Greek, which means "4" in translation. Therefore, the structure of the original Tessar is composed of 4 lenses. 4 groups of pieces, and then continued to be dismantled into 2 pieces and 4 groups independently, and finally changed to 3 pieces and 4 groups with the front group separated and the back group glued together. The tossing back and forth also shows that in that era without computer aids, The quality of a lens design can only be known after it is manufactured and used. The predecessors planted trees and the descendants took advantage of the shade. Now we really need to hold a respectful attitude when playing with cameras.

So for Tessar, it is necessary to figure out a premise that it is small not because it is advanced, after all, it was published in 1902.You should be able to understand through the piles written above that no matter Rapid Rectilinear or Triplet coexisting with Tessar, everyone’s structure is very simple, but why is Tessar can be used simply by changing it on the basis of retaining the original? On a body as small as the Sony RX0, have other structures been eliminated one after another?The reason is that the most important thing is to take the right route of performance characteristics, and take advantage of the manufacturing difficulty and low cost.

Let’s first look at its performance. First of all, its optical quality can be improved very much. The lens in the 1950s can’t even meet the resolution of 1000 million pixels, let alone a mobile phone can easily achieve 1000 million. resolution.The Tessar structure has a strong ability to suppress distortion, coma, and axial dispersion. The structure is very compact and easy to modify. For example, the Canon 40mm F2.8. Spherical, but the weight is only 6 grams, so Tessar can also be seen on the lens of many mobile phones.

However, it is precisely because the size is too compact and there is no space to design a large entrance pupil diameter, so the aperture of the Tessar lens is generally small. As the second oldest structure after Pl.anar, it is based on the various biscuit heads designed It is not difficult to find on various bayonet bodies, and the price/performance ratio is very high.

④ Lens coating

Generally speaking, everyone will think that the lens is an extremely smooth and transparent lens that has been polished.

However, when it comes to strict optical standards, this smoothness and light transmittance are not enough.

The earliest camera lenses did not have the concept of coating, including the matting treatment inside the lens barrel and the imaging treatment at the edge of the lens, which are far below the level of today's lenses.

Later, in 1982, H.Dennis.Taylor from the United Kingdom accidentally discovered that the surface of the burnt telescope objective lens produced a purple film through weathering. On the contrary, it can transmit more light than ordinary lenses, so this is the original coating. Prototype.

The light transmittance of pure glass is about 95%, and 4~5% of the light will be lost.

However, a lens is not just a single lens, it is composed of multiple sets of lenses, so when there are many lenses, the loss rate of light transmission will increase exponentially, even up to 50 % loss.

Interfering the light transmittance by coating can greatly increase the light transmittance, and the effect of increasing the number of coatings (each lens and the air contact surface of each lens) can be superimposed.

Although there are remarks that the correction of light transmission through coating is far less effective than optimizing the lens structure, lens material and polishing process.

However, since the development of coatings, it has been possible to achieve a reflectance of close to 0% for visible light, and has a multi-layer coating technology, including the coating of each air surface.

In this way, the cost of materials and processes for lens glass processing can be greatly reduced, and excellent effects can also be achieved through multiple interferences of coatings. (We all know that the early lenses were luxury goods, which could not be touched by the public, because the yield rate was low and the cost was extremely high. Now it has become a mass consumer product.)

There are many functions of coating, which can be roughly divided into seven types: anti-reflective coating, reflective coating, filter coating, polarizing coating, protective coating and electric heating coating.

Just looking at the name is also easy to understand, some are for increasing light transmittance, some have the same polarizing effect and so on.

However, with so many functions added to a lens, it has to rely on the technology of multi-layer coating.

In 1971, Pentax launched the SMC super multi-coated Taikuma lens, and the number of coating layers exceeded 7 layers. The SMC coating has a light transmittance of 99.8% and a reflectivity of only 0.2%.

Prior to this, Nikon, Canon and Leica had mastered 3-4 layers of coating technology, but there has been no breakthrough in more than 6 layers of coating.

And Fuji's Electron Beam Coating EBC claims that it can reach 11 layers of coating.It was only used for movie lenses at that time, and it was not used for civilian use.

Then Pentax made a lot of money with SMC technology patents before each company solved their own coating problems...

Due to Pentax's pressure on the market, Fuji finally developed the EBC and Super EBC FUJINON photography lenses.

Now, basically every major lens manufacturer has its own coating technology to serve the lens

Zeiss’ famous T* coating, Canon’s SWC coating, Nikon’s NCC coating, etc., Fuji’s EBC, Schneider’s HTF, etc.

The biggest shortcoming in the comparison between the sub-factory lens factory and the original lens factory is the coating technology.

For example, the domestic Laowa is already very good in other aspects, but the coating is not as good.

The effect of coating