The role of polarizer

1, improve the blue sky tone and color. A polarizer can block part of polarized light without affecting or basically affecting the original colors (such as light-dark contrast Lb, black-and-white contrast) and colors (such as color reproduction and color contrast Lb) of other parts of the scene. So the polarizer can darken the brightness and hue of the blue sky with polarized light. This can not only adjust the tone of the sky more appropriately, but also narrow the contrast between the sky and the ground scenery, making the contrast and tone between them more balanced and harmonious. At the same time, the polarizer can also improve the hue of the blue sky, making the blue sky in color photos bluer and more saturated, thus making the white clouds more prominent and vivid. In the whole blue sky, the polarized light is the strongest and most in the area 90 to the direction of sunlight projection, so a large amount of polarized light is scattered over the south, north and overhead in the morning and evening, and a large amount of polarized light is scattered in the sky in the north, east and west at noon (including the south in summer in southern China). Obviously, when using a polarizer to adjust and control the hue of the blue sky, it is advisable to make the shooting direction just perpendicular to the direction of sunlight projection (even if the photographer's index finger and thumb are at a 90-degree angle, when the index finger points to the sun, the blue sky polarized in the direction pointed by the photographer's thumb is the most, so the best effect of darkening the blue sky can be obtained by shooting with a polarizer). See the above picture (using skills). When taking landscape photos with black and white film, the combination of polarizer and yellow filter can get the picture effect of blue sky, dark gray and bright white clouds.

2. Simulate the night scene effect. In black-and-white photography, because the polarizer can darken the blue sky tone with polarized light, it is often combined with a red filter to shoot a picture simulating the moonlit effect with black-and-white film in the sun (the exposure should be appropriate and insufficient). Polarizers are also often used in color photography to darken the blue sky to simulate the night scene effect in the sun. When shooting, the face is at 90 degrees to the sun. In the direction of the blue sky in the corner, Leiden 85B is not added, and the B-type color film is directly used to shoot, and the sky shadow is darkened by the polarizer in front of the camera lens. In order to simulate the realistic moonlit effect, the exposure of the sky should be less than 1.5 when shooting, and the light with a color temperature of 3200K can be used to properly supplement the light-receiving surface and backlight surface of the face. Although this method can push and pull sports photography when shooting, it is not suitable for horizontal panning, lest the change of sky density make the simulation of film "worn" when panning to different azimuth angles. 3. Improve the image clarity, texture and color saturation of the flare part on the surface of nonmetallic objects. Generally, when white light shines on an ordinary object, the surface of the object will absorb some colored light and reflect the other part, so that human eyes can know the inherent color of the object from the reflected colored light. However, when high-intensity white light (such as outdoor sunlight) shines on the surface of a smooth object, the object will not only reflect a part of colored light that reflects the inherent color of the object, but also directly reflect a considerable part of all colored light emitted by the light source without being absorbed (if the light source is sunlight, this part will be reflected as white light without any color). In the highlight part of a smooth object, the intensity of the latter reflection is much greater than the former, which makes the highlight part of the object form bright spots and flares, weakens the color tone of the object itself, and makes it appear as a light source color, thus significantly reducing the color saturation of the object there. For example, in the sun, the highlight of the roof reflects strong white light, which often makes this part of the body color unsaturated. Another example is the wet grass with dew and water drops, and the green color often looks pale. On sunny days, some green leaves and grass areas will reflect a lot of blue light, showing a tendency of light blue and cool colors. When the brightness of the bright spots on the surface of an object is too high (too dazzling), the area is too large, the position is not good, or there are too many flares, it will often have a bad influence on the hue and color of the whole picture, which will damage the level, detail, texture, clarity and color reproduction of the bright spots and flares to a certain extent, which will easily interfere with the audience's line of sight. In many occasions in real life, at the bright spots and flares on the surface of non-metallic objects, the reflected light that can present the inherent color of the object is natural light (i.e. unpolarized light), while the strongly reflected light that presents the color of the light source is polarized by the surface of the object-turned into polarized light. Obviously, at this time, polarized light can be easily eliminated by polarizer.

The bright spots and flares formed by the polarizer can truly record the inherent color tone and reproduce its texture. For example, when shooting glassware, porcelain, painted objects (such as furniture, car paint), waxed floors and plastics, with thin waxy green leaves and fruits growing on the surface, and landscapes with large areas of water (such as sea and lake), and when remaking works of art and photography (such as photos and oil paintings) and materials, photographers often use polarizers and adjust their orientations appropriately. For another example, some green leaves and fruits reflect a lot of blue skylight on sunny days and linearly polarize it. Therefore, using a polarizer and properly adjusting its orientation can obviously weaken the blue polarized light reflected by such green leaves, green grass and fruits, thus correcting the tendency of light blue and cool tones caused by reflection and making the colors such as green more saturated. In a word, the polarizer can obviously weaken or even eliminate the smooth surface of some opaque non-metallic objects, as well as the strong bright spots and flares on the surface of transparent objects and other harmful reflections with excessive brightness. Therefore, the polarizer can not only significantly improve the image clarity of such bright spots, but also truly show the inherent color of objects covered, blocked and diluted by highlights at such bright spots, and significantly improve the color saturation of their images. Therefore, the photographed images have rich layers, clear details, distinct textures, delicate shadows, harmonious colors, strong texture, bright, rich, magnificent, rich and pleasing to the eye.

4. Improve the image clarity and color saturation of the scene inside or behind the transparent object. The polarizer can obviously weaken or even eliminate the harmful reflection and mirror image on the smooth surface of transparent body, and can also take a complete and clear picture of the scenery inside or behind transparent body. For example, the smooth surface of transparent objects such as glass surface and water surface is not only easy to generate strong reflection, but also easy to reflect a clearer image of the object in front-mirror image (such as reflection on the water surface, pedestrians and streets reflected by window glass). Therefore, when the photographer shoots the subject in the water or behind the window glass, the above strong reflection and mirror image have the adverse effects of shielding, shielding and interference, which often makes the shape and color of the subject appear incomplete, very messy, fuzzy and unclear, and the contrast is weakened. If the polarizer is used properly, it can obviously weaken or even eliminate the interference and bad influence of harmful reflection and mirror image on the photographed object, and make the window glass and water surface more transparent, so that a clear image of the blocked object appears on the screen. 5. It can be used as a substitute for ND5 neutral density filter in an emergency. Because the polarizer only allows light waves in the same vibration direction to pass through, all unpolarized colored light will be uniformly filtered and weakened after passing through the polarizer, so in an emergency, the polarizer can play the role of a corresponding neutral density mirror. For example, when the light is too strong and it is necessary to shoot with a larger aperture or a longer shutter time.

6. A pair of polarizers can form an adjustable reducing mirror. When a pair of linear polarizers overlap each other, the total optical delay can be changed by changing the included angle between the polarization directions of the two polarizers: when the polarization directions of the two polarizers are the same, the total optical delay is the smallest; With the increase of the angle between polarization directions, the total light blocking rate also increases; When their polarization directions are perpendicular to each other, the total light blocking rate is the largest. In a word, a series of optical delay values can be obtained by two superimposed linear vibrating mirrors, which can replace the role of several ND mirrors. Therefore, the two superimposed polarizers are also called adjustable neutral decompressors, commonly known as adjustable decompressors. The front linear polarizer and the reverse circular polarizer (or the back forward circular polarizer) can also form an adjustable reducing mirror. After two linear polarizers are superimposed on each other, they are placed at the front end of the cinematographic lens, and when shooting, one of the polarizers is rotated evenly, that is, the included angle between the polarization directions of the two lenses is changed evenly, so that a cinematographic picture with "fade-in" and "fade-out" effects can be shot. Note: There is no linear relationship between the increase of the included angle in the polarization direction of the two lenses and the increase of the total light blocking rate, for example, when the included angle changes from 0. Increase to 10. The increase of the total light blocking rate is very small (about 65438 0.03 times), but when the included angle is from 74. Increase to 84. , although still increased 10. However, the multiple of the total light blocking rate increases sharply (about 8 times). Therefore, when shooting the "fade-in" effect picture with two superimposed linear polarizers, the rotational angular velocity will gradually slow down with the increase of the included angle of polarization direction; On the contrary, you should turn faster and faster when shooting the "gradient" effect. 7. A pair of polarizers (plates) can eliminate the intense flash on metals and other objects. By placing a large lamp linear polarizer and a common polarizer in front of the illuminating lamp and the photographic lens respectively, and properly adjusting the relative included angle between the polarization directions of the linear polarizers, the intense glare on the surface of the illuminated metal object or nonmetal object can be weakened or even eliminated at will, without basically affecting the lighting effect of the lamp on other parts. Because when shooting, despite

The direction of illumination is different from the incident angle of illumination light, but the reflected light at the bright spot of the subject is mostly linearly polarized light. Therefore, as long as the polarization direction of the polarizer in front of the camera lens and the polarization direction of the linear polarizer in front of the light are perpendicular to each other (or at an angle of several tens of degrees), the polarized light reflected at the bright spot can be completely absorbed (or partially weakened). However, the non-bright spots of the subject can depolarize the incident polarized light, so a clear image can still be formed on the photosensitive film through the linear polarizer in front of the photographic lens. When shooting, it is generally not necessary to add a linear polarizer in front of each lamp, just add a linear polarizer in front of the lamp that produces strong glare. This method has been widely used in still life photography, advertising photography, animation photography and other fields.

8. When remaking materials, use polarizers and polarizing plates for lamps to eliminate strong reflections and bright spots on the surface of objects (such as oil paintings). The measures are as follows: Install the lamp polarizing plate at the front end of the lamp which is located on both sides of the camera and illuminates at an angle of 40 with the remake plane. Install a linear polarizer on the camera lens, and rotate the polarizer on the camera lens until the strong reflection bright spot formed by one side lamp is eliminated (only the side lamp is lit at this time). Then turn off the illumination lamp, turn on the illumination lamp on the other side, and rotate the polarizer in front of the polarizing photographic lens in front of the illumination lamp until the strong reflection bright spot formed by the illumination lamp on this side is also eliminated. After that, you can turn on two lights at the same time and take a new shot.