What is a CPL polarization filter? This is a valuable device that any photographer should have in his bag. How does the polarizer affect the picture? In order to develop intuition about this point, very often it takes a long experiment. In this article you will learn how to speed up this process, how and how this product can facilitate the task (and sometimes harm) in different situations.
Where is the CPL filter attached? It is always in front of the front lens of the lens. How does this device work? It filters direct reflections of the sun's rays at specific angles. This is not out of place, since other light is often rich in shades and more diffused. Working with this device also requires an increase in shutter speed (as some beams are deflected). The control of the filtration angle is due to the rotation of the device. The strength of the effect depends on finding the camera line of sight relative to the sun.
Filter rotation
When can I get the maximum effect with a CPL filter? Only if the line of sight of the camera is perpendicular to sunlight. This can be imagined by pointing the index finger towards the sun, while placing the thumb at a right angle to it. While you rotate your hand, pointing to the daylight, any course that your thumb points at will determine the line of the highest polarizer effect.
However, the fact that the CPL filter will provide the best result in these areas does not necessarily mean that it will be most noticeable in them. The maximum polarization will appear during its rotation, which will change the angle relative to the daylight. To feel the filter, it is best to rotate it, looking at the camera display or in its viewfinder.
When using a wide-angle lens, you can get the wrong result, since the polarization effect depends on the angle. One part of the picture can be placed at right angles to the sun, and the other in the direction of it. In this case, the polarization effect will not be noticeable on one side of the photo, and it will be visible on the other.
Obviously, wide-angle lenses are imperfect. However, the turns of the "polar" can sometimes make the effect more vital. Very often, professionals place the most pronounced effect of polarization closer to the edge or corner of the picture.
Description
Photographers use two types of filters to create high-quality images: linearly polarized and circular. These devices isolate and separate zones rich in polarized reflected light. With their help, removing the bottom, you can sift bright glare, or capture the landscape outside the window without its own reflection in the glass.
Linear filters perform one simple job - they transmit modified light in a single plane. Devices with circular polarization give access to beams modified in a circle. They turn any refraction of the rays into spherical. In fact, the circular "polarizer" does not interfere with autofocus, allows you to accurately guess the exposure and can be installed on all cameras (including old ones).
In this case, excessive glare will be eliminated as well as in a device with linear polarization. A CPL filter provides “pure” spherical refraction of light only at a specific wavelength. In the wave plate, the optical difference of its path between simple and extraordinary rays is exactly a quarter of its length. For all other wavelengths, this device will show an elliptical effect.
Circular filters are more complicated than others, therefore their cost is higher. A regular linear device is placed on the outside of this device, and a quarter-wave plate is turned on the inside, which converts linear polarization to spherical.
The photo
Polarizing filters for the camera are devices designed to eliminate unwanted effects (reflections, glare), weaken the brightness (with a parallel increase in saturation) of the sky and other objects, to achieve aesthetic goals. They look like ordinary filters, but have front and back parts of equal thickness that can rotate freely.
How is a CPL filter applied? What is this device for? Its back is screwed to the lens, and the desired effect is selected by rotating the front half by any angle. The front segment can be equipped with an internal thread, with which an objective cover, a threaded hood or other filters are attached, which is an irrefutable advantage.
Different segments of the reflecting objects can give a reflection with different angles of polarization, which cannot be suppressed synchronously with a single filter. In addition, there may be a large number of casting objects in the frame. In such cases, several sequentially twisted polarizing filters are used, and all but the back should be linearly polarized. This is necessary because the optical compensator placed in the circular filter prevents the effect of other devices that can be placed behind it from being achieved.
What else is the polarizing filter for the lens famous for? Its optical density is usually located in the range of two to five. Color distortion may occur. In general, some devices have a drop to one stop in the violet-blue region, which is why the picture turns out with a green tint. Cheap devices can disgustingly reproduce small details. Polyarik, along with a “protective” UV-obstructing filter, is the most used device in photography.
Details
Typically, a polarizing filter is produced in the form of two plates made of glass. Between them there is a polaroid film with linear dichroism. This part is a certain layer of cellulose acetate containing an impressive number of the smallest microlites of hepatatite (iodide compound of quinine sulfate).
Such polyvinyl iodine films with polymer chains synchronously oriented are used. The orientation of the microliths is identical due to the electric field, and the polymer chains are guided by mechanical tension. The circular filter, in addition, is equipped with an optical compensator - a quarter-wave phase plate. Using this part, you can determine the difference in the stroke of the two ray launches. It works in accordance with the phenomenon of birefringence of light in crystals.
Turning light
Simple and exceptional rays have different speeds. Their optical path lengths are also unequal. Therefore, they acquire a stroke difference, measured by the thickness of the crystal through which they pass. It is installed along the path of the traveling beam behind the polarizer and rotates during assembly until its oscillation axes coincide with the optical axes.
In this position, the quarter-wave plate converts the rays polarized linearly into light with circular polarization (and vice versa), increasing the travel difference to 90 degrees. With such features, all the "polarists" are made. The difference in price and quality is due to additional layers: protective, antireflective, water-repellent.
Appearance
When was the polarizing filter for the lens designed? This product appeared due to the development of TTL elements of camera automation, which, unlike photographic materials, became dependent on innovative exposure to light.
In general, linearly polarized radiation complicates exposure metering and, in SLR cameras, partially impedes the action of phase focusing automation.
In astronomy, the "polarists" are part of the devices with which they study the circular and linear changes in the light of objects in outer space.
Polarization surveillance is the basic way to obtain information about the magnetic field power in areas of radiation generation, say, on white dwarfs.
Nikon CPL
The Nikon 52 mm CPL polarization filter is a valuable item for a landscape photographer and for those who like to get high-quality images. There are at least six reasons why you need to purchase this product:
- For photographing water (it becomes darker and more transparent).
- Shooting a landscape (increasing the "saturation" of greenery and sky).
- For shooting at an angle through the window (to destroy glare and reflections from the glass).
- Elimination of reflections on a sunny day (from water, glass, cars).
- Increase exposure by a couple of stops (when needed).
- Protect the lens from mechanical stress.
You need to buy this filter for those who go to travel to warm countries - this is an indispensable assistant in the manufacture of colorful photos. In bright sunshine, this device improves image quality, increasing contrast and saturation, while eliminating haze.
Limitations
Those people who want to learn how to take good pictures take photography lessons from professionals. How to use a polarizing filter? The device of the desired diameter must be screwed onto the camera lens. By rotating the crystal in the filter, it is necessary to select the desired degree of polarization, which will allow eliminating glare from water or glass during shooting, as well as get more fluffy and white clouds, saturated sky.
There are some restrictions on the use of such devices:
- Rotating the polarizing filter, it must be taken into account that the expected region of the limiting effect will be located approximately 90 degrees from the primary position. If the device is rotated 180 degrees, this maneuver of the picture will lead to the initial state.
- "Polarians" soften the luminous flux entering the camera matrix through the lens, so professionals often increase exposure balancing by 1-2 steps.
disadvantages
Photography lessons are needed for aspiring photographers to create quality shots. We found that the "polarists" are very useful. Unfortunately, they have the following disadvantages:
- Because of this device, the exposure may ask for 4-8 times more light (2-3 steps) than usual.
- They need a certain angle with respect to the sun to get the best result.
- It is difficult to navigate with these filters by the camera viewfinder.
- These are some of the most expensive appliances.
- They require rotation, so they can increase the time of selection of the composition.
- Usually they cannot be used for wide-angle and panoramic shots.
- If the filter is dirty, it may reduce picture quality.
Moreover, sometimes reflections are needed in photographs. The most striking examples here are rainbows and sunsets. It is worth applying a polarizer to any of them, colorful reflections may disappear completely or fade.
Other recommendations
Filters for the camera are complex devices. But over time, you can learn to work with them. Polyarik can sometimes be used when it is necessary to increase the exposure duration. Since it can reduce the transmitted light by 4-8 times (by 2-3 steps), it can be used to remove water and waterfalls.
If you put the polarizer on a wide-angle lens, it can create a flashy darkening of the edges of the picture (“vignetting”). To avoid this, you will probably have to purchase a more “thin” expensive option.
Circular polarizers were created so that the autofocus and metering systems of the camera continue to work when the filter is on. Linear “polarizers” are much cheaper, but they cannot be used with most SLR digital cameras (since they use phase detection autofocus and TTL metering through the lens).