The functions and differences of UV mirrors, polarizers, and filters
UV Mirror - UV is actually the English word for Ultraviolet; The abbreviation for Rays (ultraviolet light):
For shooting, no filters should be the best. Especially when facing a light source, the glare caused by UV mirrors will definitely affect the image. The purpose of coating is to minimize the generation of glare as much as possible. Multi layer coating UV means coating 6-8 layers of film on each side of the lens to ensure a transmittance of over 95%. So it is recommended to purchase multi-layer coatings with higher transmittance for UV lenses. Buying some UV is to minimize the adverse effects of UV on exposure and glare while protecting.
When it comes to protective lenses, almost everyone needs a UV lens to act as a protective measure. In daily use, as long as you are careful, the lens will generally not be stained because the lens cover can be covered at any time. But there are still times when one is not careful. It hurts when the lens gets dirty, and wiping it may scratch the lens. Moreover, only the lens cover is used. Once the fleeting beauty is discovered, it takes time to remove the lens cover, which can easily miss a good opportunity. So, one UV The mirror has become the protective cover that everyone needs now. UV lens is one of the essential components of a lens. Its main function is to prevent ultraviolet rays, reduce the transmission of blue and purple light waves to the photosensitive material, make the distant view clear, and improve the contrast and color saturation of the distant view. Although the CCD and CMOS used in DSLRs are not as sensitive to ultraviolet radiation as film, we still recommend installing a high transmittance UV lens to protect the lens from contamination or damage. Compared to cheaper double-layer coating UV, multi-layer coating UV has higher transmittance.
For some lenses, there is still a problem with adding UV lenses, which is that after adding UV lenses, it is impossible to cover the lens cover. In this case, some people use tools such as knives and files to saw the screws on the edge of the lens short in order to cover the lens cover. This way, they can add both UV lenses and the lens cover. However, this method carries a certain level of risk. Such an expensive item could be disastrous if it fails. The second method is to add UV lenses during filming. Usually, remove the UV lenses and cover them with the original lens cover. Although it may be a bit troublesome, there is no risk involved!
Polarizing mirror
The function of a polarizing mirror is to eliminate harmful reflected light, such as light reflected from glossy surfaces such as water or glass, improve the clarity and expressiveness of images, and increase color saturation. For example, it can make the colors of blue sky, green leaves, ridges, and buildings more vivid. The most important point is that the effects created by polarizing mirrors cannot be reproduced by Photoshop, while the effects of other filters such as dimmers, grayscale mirrors, soft focus mirrors, fogging mirrors, and various colored filters can be basically achieved through post-processing by computers. Although polarizers are only optional filters, they are still indispensable for friends who enjoy landscape photography or are interested in photography creation.
To understand a polarizer, we first need to know what polarized light is.
Camera cannot do without light, which is also an electromagnetic wave that can vibrate in any direction on a plane perpendicular to its propagation direction. In general, natural light vibrates uniformly in all directions. When the subject is non-metallic and has a smooth surface, under a certain natural light irradiation angle, the reflected light is not only the natural light that vibrates uniformly in all directions, but also a part of the light wave that vibrates in one direction, which is called polarized light. These light rays containing natural light and polarized light enter the camera through the lens and form an image. When we look at these captured images, we often find that the glare formed by polarized light in the picture destroys the completeness of the image. For example, when we are shooting the subject in a shop window, due to the reflection of glass; Polarized light causes the subject in the shop window to be unclear; The green leaves of flowers captured from certain angles turn gray or white; In landscape photography, the blue sky captured is not blue enough, and there are unsightly reflections on the water surface. Therefore, in many cases, polarized light is harmful to photography. So how to solve the impact of polarized light on camera? We can install a polarizer to solve this problem.
Polarizer is an additional mirror attached to a camera lens that can eliminate or partially eliminate polarized light. Polarizers are generally made by bonding polyvinyl alcohol films that have been impregnated and processed with iodine between two flat optical glasses. It can allow linearly polarized light with the same polarization direction to pass through approximately; 80% of the light intensity, while linearly polarized light vibrating perpendicular to its polarization direction can only pass through less than 1%. The mirror surface color of the polarizer is close to black, and the outer edge of the lens can rotate. It consists of a lens body and a rear seat frame that is connected to it and can rotate. The lens body is composed of a grating made of extremely fine crystal glass. When rotating, this grating will block polarized light rays that are not parallel to it. Therefore, a polarizing mirror can control and select the number of parallel reflected light (which is polarized light) recorded on the film.
Polarizer is also a widely used additional lens. Its function is to effectively reduce or eliminate the reflection of non-metallic surfaces. Polarizers can be used in both black and white and color photography; Because it can reduce the brightness of light, its appearance is gray. Polarizers are commonly used in the following situations: to eliminate or reduce the surface reflection of smooth objects; Darken the color tone of the sky; Replace the medium gray filter with two overlapping pieces; And improve the saturation of color images; Improve contrast; Wait a moment. For example, when shooting scenery on water surfaces or in glass windows, polarizing mirrors can be used to eliminate surface reflections. When using, rotate the outer edge of the lens until the reflection on the surface of the scenery is no longer visible. In sunny beaches or outdoors, where there is a significant contrast between light and dark, it can be used to reduce the excessively bright areas and achieve a moderate balance between light and dark in the image.
Although polarizers are the most valuable filters in digital photography, they are not omnipotent. Polarizers also change the light ratio of various parts of the image when removing large areas of reflection, so the color tone of the image captured with polarizers may vary. For some scenarios, whether to use polarizing mirrors depends on individual needs. When the proportion of reflected highlights in the image is large, using a polarizing mirror will affect the color tone of other parts of the image; If the proportion of reflective highlights in the captured scene is relatively small, it will increase the local color saturation while the color tone of other parts of the image remains basically unchanged. Under certain lighting conditions, the polarized light content is very low, and using a polarizer will not achieve the expected effect. At the same time, due to the increase of optical lenses in the light path, it will have a negative effect on the image quality. At the same time, due to the rotating part and large thickness of the polarizer, it is easy to form dark angle phenomenon, which needs to be paid attention to during use.
There are many types of polarizing mirrors. According to the installation method, it can be divided into embedded type and external type; According to the working principle, it can be divided into linear polarizer (p l) and circular polarizer (cpl), so the suitable polarizer should be selected based on the characteristics of the camera.
Among these polarizing mirrors, the most common is a general external mounted linear polarizer (PL); Compared to a circular polarizer (CPL). Polarizers are generally composed of two parts. The rear part is connected to the camera with threads, and the front part has a filter that can rotate to reduce the passage of polarized light by changing the rotation angle. Its working principle can be simply understood as follows: natural light and polarized light in the reflected light of the subject, under the action of PL, harmful polarized light is; Filter out” Natural light partially passes through and is; Transformation” For polarized light, the light entering the lens is actually polarized light; Reflected light in; c p Under the action of l, polarized light is“ Filter out” ， Natural light partially passes through and is converted into polarized light, which then“ Circular Rotation; Next,“ Transform oneself; Once again becoming natural light, the light entering the lens is actually natural light. So, CPL is more complex than PL, which is also the main reason for the significant price difference between the two. The price of CPL is higher. The difference between PL and CPL can be simply understood as follows: regardless of the type of light that passes through PL, the light that passes through CPL is polarized light; Natural light;. Many cameras have non-metallic reflective surfaces in their metering and focusing components. Obviously, if the light entering the lens is polarized light, it may cause inaccurate metering and focusing. Designed to overcome this deficiency; cpl。 Although the light passing through CPL is still polarized, the polarization direction of the light will constantly change during propagation, which is equivalent to; Natural light; ， Therefore, it also ensures the normal operation of the camera's metering and focusing system.
In the actual purchase of polarizing mirrors, it has been found that many salespeople of merchants cannot distinguish them clearly; PL and CPL, Therefore, we need to judge ourselves. Place the polarizer close to the eyes and observe the reflection of non-metallic scenes. Rotate the polarizer to a certain angle, and the reflection will weaken or even disappear; By reversing the polarizer and conducting the same experiment, PL will see the same results, while the scene observed with CPL remains largely unchanged.
Linear polarization is a common polarizing film, where light passes through in a single polarization direction. Circular polarization is the addition of a lens on top of linear polarization, which transforms polarized light into a circularly polarized state, also known as light that is no longer polarized. Simply put, light that has undergone linear polarization is polarized light, while light that has undergone circular polarization is not polarized light. This is the biggest difference between them.
The specific adjustment method of polarizing mirror is as follows:
Install the polarizer directly at the front end of the camera lens, slowly rotate the polarizer, and observe the polarized light source in the subject through the LCD screen or viewfinder until it disappears or weakens to the expected effect; You can also place the polarizer directly in front of your eyes and rotate it while framing until the polarized light disappears or weakens to the expected size. Then, while keeping the orientation of the polarizer unchanged (i.e. the direction indicated by the markings on the edge of the polarizer remains unchanged), translate the polarizer and place it at the front end of the photographic lens. Afterwards, the camera cannot change the shooting direction arbitrarily, otherwise the polarization direction of the polarizer must be readjusted.