[Usage of polarizer] How to use polarizer and what is the main purpose of polarizer
How to use polarizers
There are two types of polarizers: Circular polarizer (referred to as CPL) and linear polarizer (referred to as PL or LPL).
They won’t make a difference on most consumer digital cameras (DC), if you have a modern (with autofocus and TTL metering) SLR/DSLR also has DC , and if you want to share a polarizer, it is best to choose a circular polarizer. In addition, the differences between linear polarizers and circular polarizers, as well as the reasons why modern SLRs/DSLRs use circular polarizers, are very carefully explained in Chapter L.6 of my book; but because it is not important to beginners, so here It is omitted, and interested friends, please refer to my book (there is a PDF file of this chapter in the link above).
The polarizer has a ring that can be rotated freely, and its function is to adjust the effect of the polarizer. There are usually two types of polarizers: thick (general) and thin. The former may be 1mm thicker or more than the latter. When referring to polarizers below, if there is no special description, it refers to thick (or general) polarizers. Thin polarizers are for wide-angle or ultra-wide-angle lenses, because too thick polarizers are prone to vignetting. Generally speaking, if the equivalent focal length of the camera lens (135 film) is more than 35mm (including 35mm), the thick polarizer should not produce vignetting; but if the focal length is less than 35mm, the thick polarizer is likely to produce vignetting, but This is usually related to the optical and mechanical structure of the camera lens, not every lens, so it is best to try before buying polarizers.
The main purpose of polarizers:
Reduce the reflection of glass, water and non-metallic Become more blue, and increase the saturation of the color of the picture. Because the polarizer is dark gray, it will block part of the light that can reach the photosensitive chip, which is generally reduced by 1 to 1.5 stops. Except in full manual exposure mode, the metering system of the camera will adjust itself in other modes (such as aperture priority, or shutter priority), but you still have to check whether the aperture or shutter speed selected by the camera is suitable.
Reduces reflections
Reflections on the subject surface wash out the picture One of the most important functions of the polarizer is to reduce or even eliminate the light reflected by the subject and enter the lens, but when the subject is metal, the function of the polarizer is not very significant. The best angle to use polarizers to reduce or eliminate reflections is when the illumination angle of the light source and the shooting angle of the camera are both 30 degrees from the subject, and when one (or both) deviates from 30 degrees, the effect will be reduced. And the greater the angle deviation, the lower the effect, so when using polarizers to reduce or eliminate reflections, pay more attention to the composition. Using a polarizer to reduce reflections is very simple. After the composition is complete, turn the ring in front of the polarizer. During the rotation, the viewing window (or LCD/EVF) will display the effect of the polarizer. Once the desired effect is obtained, stop the rotation and shoot. It is important to note that polarizers are not a panacea and may not completely eliminate reflections.
The most well-known application of polarizers is to deepen the blue of the sky, making the contrast between the blue sky and white clouds stronger; however, if the sky is not blue at all (such as cloudy days), no matter how good The polarized lens can’t capture the blue sky. But we should understand that only one part of the sky will become bluer, another part may not change, and more importantly, the shooting angle needs to be chosen correctly. There is a very simple rule for choosing a shooting angle. First, extend your index finger to point to the sun, then raise your thumb to be perpendicular to the index finger, and turn around the index finger, so the direction that the thumb crosses is the shooting direction that can get the greatest effect; In other words, the best shooting direction is perpendicular to the direction from the camera to the sun! Please note that the thumb crosses 360 degrees. Except for the middle of the sun, part of the 360 degrees is towards the sky and the other is towards the ground. The part towards the sky can make the blue darker and bluer. direction. The farther the camera deviates from this direction (such as the direction of the sun or the direction of the sun), the lower the effect, if the deviation is greater than a certain angle, the effect is not significant or even disappears. After finding the shooting direction, slowly turn the ring in front of the polarizer to get the desired effect and then press the shutter to shoot.
In addition, because the polarizer will reduce or even eliminate the reflection of the subject, the color of the picture taken with the polarizer is purer and the contrast is higher than when it is not used. topic for the next section.
Increase contrast and color saturation
Reflection of the subject It will cover up the original color and details. If the subject in the picture has similar reflective characteristics (such as leaves), a whole weak reflection will not only erase the original color, but also reduce the contrast of the picture. In this case, use a polarizer It has the effect of reducing reflections, reproducing the color of the subject, and improving the contrast of the picture. The bottom left photo is a polarizer with the lowest effect, and the bottom right is the maximum effect; the two are a very strong contrast, the reflection of the leaves under the hot sun distorts the color of the forest, but the effect of the polarizer is adjusted to the maximum , the color of the woods and grass is revealed, making the two photos very different.
What if the camera doesn’t have a polarizer?
Many small and stylish digital cameras can’t have filters or sleeves, but we can hold a polarizer on the Shooting in front of the lens, but how to adjust the effect of the polarizer? The method is very simple, first hold the polarizer and aim at the shooting direction of the lens (so the closer to the camera the better), as shown in the left photo below; then turn the ring on the polarizer, and stop when the desired effect is reached (bottom middle); The adjusted polarizer is moved to the front of the lens (bottom right), but the polarizer cannot be rotated, because once the direction of the polarizer is changed, the desired result will not be obtained.
Practice this procedure a few times, and then try taking some pictures to compare the results with and without the polarizer, and after a few times, you will be handy. Most compact digital cameras have very small lenses, and a 37mm polarizer is usually large enough (if 37mm is too small, go with a 43mm; if 37mm is too big, try a 28mm), bring a polarizer with you The mirror can easily take photos with saturated color, blue sky and white clouds, and high contrast when traveling.
Notes on using polarizers
First, polarizers may It is the most important filter in digital photography, it can reduce or even eliminate the light reflected by the subject, turn the sky blue, and improve the contrast and color saturation of the picture.
Second, most consumer digital cameras can use linear polarizers, but most (especially those with autofocus and metering) SLRs/DSLRs usually only Use circular polarizers. If you use a polarizer at the wide-angle end and there will be vignetting, you should use a thin polarizer.
Third, the use of polarizers will lose 1 to 1.5 levels of light, which will affect the chosen aperture or shutter speed; A wide aperture (so depth of field becomes shallower), or a slow shutter speed (so moving subjects may be blurred and prone to camera shake), so you should pay attention to aperture and shutter speed.
Fourth, although the polarizer has the effect of reducing reflections and turning the sky blue, this effect is related to the shooting angle. If the shooting angle is wrong, the expected effect may not be obtained. . Also, when shooting with a wide-angle or ultra-wide-angle lens, the sky may appear blue in the frame from very dark to fairly light, i.e. uneven in density, because the angle of view may be greater than the optimal angle of the polarizer.
Fifth, it is best to remove the polarizer from the lens when it is not needed. First, the polarizer will block the light of class 1 to 1.5. Second, it is because Regardless of where the polarizer’s effect is positioned, its effect is more or less present, so polarizers can sometimes have counter-effects (such as filtering out the desired reflections).
This article introduces the basic concept, usage, and effects of polarizers, and lists some precautions when using polarizers. The effect of polarizers is difficult to simulate with post-production software, even when turning the sky blue. If the boundary between the sky and the ground is relatively simple, it is easier to select the sky and change the color depth in post-production. Once the boundary becomes very complicated, choosing the sky part is a time-consuming and labor-intensive task, so instead of doing post-production It takes a lot of trouble, and it is better to use a polarizer to adjust the effect when shooting. Furthermore, if the picture loses details due to reflections, no matter how good the post-production skills are, there is no way to create the unrecorded details and tones out of nothing. For these reasons, the polarizer is a filter that cannot be completely replaced by post-production software.