CPL filter with circular polarization. Photography lessons

What is 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 an intuition about this moment, very often one has to experiment for a long time. In this article, you will learn how to speed up this process, how and how this product can facilitate the task (and sometimes also cause 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 certain angles. This is not out of place, since other light is often rich in shades and more scattered. Working with this device also requires an increase in exposure (since some rays deviate). The filtration angle is controlled by rotating the device. The strength of the effect depends on finding the camera's line of sight relative to the sun.

Rotate the filter

When using the CPL filter you can get the maximum effect? Only if the line of sight of the camera is perpendicular to sunlight. This can be imagined by pointing the index finger in the sun, while placing your thumb at right angles to it. As long as you rotate your hand, pointing to the daylight, any course your thumb indicates will determine the line of the highest polarizer effect.

However, the fact that the CPL filter will provide the best result in these directions does not necessarily mean that it is in them that its work will be most noticeable. The limiting polarization will appear with its rotation, which will change the angle relative to the daylight. To feel the work of the filter, it is best to turn it, looking at the camera's display or in its viewfinder.

When using a wide-angle lens, you can get an inappropriate result, since the polarization action depends on the angle. One part of the picture can be placed at right angles to the sun, and the other - towards it. In this case, on one side of the photo the polarization effect will not be noticeable, but on the other side it will be visible.

Obviously, wide-angle lenses are not perfect. However, the turns of the "Polarist" 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: linear polarization and circular. These devices isolate and separate zones rich in polarized reflected light. With their help, removing the bottom, you can weed out bright glare, or capture the landscape outside the window without your own reflection in the glass.

Filters linear perform one simple job - they modify the light in a single plane. Devices with circular polarization give access to the rays, modified in a circle. They make any refraction of the rays into a spherical one. In fact, a circular "polarizer" does not interfere with the operation of the autofocus, allows you to accurately guess the exposure and can be installed on all cameras (old including).

Moreover, excessive glare will be eliminated as well as in a device with linear polarization. CPL-filter gives "pure" spherical refraction of light only at a specific wavelength. In the wave plate, the optical difference of its motion between simple and extraordinary rays is exactly one quarter of its length. For all other wavelengths, this device will show an elliptical effect.

Circular filters are more complicated than others, so their cost is higher. On the outside of this device is placed a conventional linear device, and from the inside - a quarter-wave plate that converts linear polarization into a spherical polarization.

The photo

Polarization filters for the camera are devices designed to eliminate undesirable effects (reflections, flare), dimming the brightness (with a parallel increase in saturation) of the sky and other objects to achieve aesthetic goals. They look like ordinary light filters, but they have a front and back parts of equal thickness, which can rotate freely.

How does the CPL filter work? What is this machine for? Its rear part is screwed to the lens, and the desired effect is selected by turning the front half to any angle. The face segment can be equipped with an internal thread, with which the objective cover, threaded hood or other light filters is fastened, which is an irrefutable plus.

Different segments of the reflective objects can give a reflection with different polarization angles, which can not be suppressed synchronously by a single filter. In addition, in the frame of the casting objects there can be a large number. In such cases, several sequentially twisted polarization filters are used, and, all but the rear, must be linearly polarized. This is necessary because the optical compensator placed in the circular filter prevents the effect from other devices that can be placed behind it.

What else is the polarizing filter for the lens famous for? Its optical density is usually located in the range from two to five. There may be color distortions. In general, some devices have a drop to one stop in the violet-blue area, which makes the picture with a green tint. Cheap devices can disgustingly reproduce small parts. "Polarik", along with a "protective" UV-blocking filter, is the most operated device in photography.

Details

Usually a polarizing filter is produced in the form of two plates made of glass. Between them is placed a polaroid film, which has a linear dichroism. This detail is a certain layer of acetylcellulose, containing an impressive number of the smallest microlites of gerapatite (iodide compound of sulphate quinine).

Such polyvinyl-iodine films with polymer chains synchronously oriented are used. The orientation of microlites is identical in view of the electric field, and the polymer chains are directed by mechanical stretching. The circular filter, in addition, is equipped with an optical compensator - a quarter-wave phase plate. With this part, it is possible to determine the path difference between two beam starts. It works in accordance with the phenomenon of double refraction of light in crystals.

Transformation of light

Simple and exceptional rays have different speeds. Their optical path lengths are also not the same. Therefore, they acquire a path difference, measured by the thickness of the crystal through which they pass. It is installed along the path of the walking beam behind the polarizer and rotated during assembly until its oscillation axes coincide with the optical axes.

In this position, the quarter-wave plate transforms the rays polarized linearly into light with circular polarization (and vice versa), increasing the path difference up to 90 degrees. With these features, all the "Polaricians" are made. The difference in price and quality is due to the additional layers: protective, antireflective, water-repellent.

Appearance

When was the polarizing filter developed for the lens? This product appeared due to the development of the elements of TTL camera automation, which, unlike photographic materials, came into dependence on the innovative impact on light.

In general, linearly polarized radiation hinders the metering and, in SLR cameras, in part interferes with the effect of phase-focusing automatics.

In astronomy, the "Polaricians" are part of the devices with which they study the circular and linear change in the light of objects that are in space.

Polarization supervision is the basic method of obtaining information on the power of the magnetic field in the regions where radiation is generated, say, on white dwarfs.

Nikon CPL

Polarizing filter CPL Nikon 52 mm is a valuable thing 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 of the landscape (increases the "saturation" of greenery and sky).
• For shooting at an angle through the window (to eliminate glare and reflections from the glass).
• Elimination of reflections on a sunny day (from water, glass, machinery).
• Increase the exposure for a couple of stops (when needed).
• Protection of the lens from mechanical impact.

To buy this filter is necessary for those who go to travel to warm countries - it is an indispensable assistant in the manufacture of colorful photos. In bright sun, this device improves the quality of the image, increasing the contrast and saturation, while eliminating the haze.

Restrictions

Those people who want to learn how to take good pictures, take photography lessons from professionals. How to use a polarization filter? The device of the desired diameter must be screwed onto the camera lens. Rotating the crystal in the filter, you need to choose the desired degree of polarization, which will allow you to eliminate the glare from water or glass, and also get more fluffy and white clouds, saturated sky.

There are some restrictions on the use of such devices:

• Rotating the polarization filter, it is necessary to take into account that the expected area of the limiting effect will be located approximately 90 degrees from the primary position. If the device is rotated 180 degrees, this maneuver image will lead to the initial state.
• "Polarizers" soften the light stream that enters the camera array through the lens, so professionals often increase exposure balancing by 1-2 steps.

disadvantages

Photography lessons are necessary for beginning photographers to create high-quality images. We found out that the "Polaris" are very useful. Unfortunately, they have the following drawbacks:

• Because of this device, the exposure can ask for more light 4-8 times (2-3 steps) than usual.
• They need a certain angle with respect to the sun for the best result.
• With these filters on the camera's viewfinder it's difficult to navigate.
• This is one of the most expensive devices.
• They require rotation, so they can increase the picking time.
• Usually they can not be used for wide-angle and panoramic shots.
• If the filter is dirty, it can reduce the picture quality.

Moreover, sometimes reflections are needed in the photo. The most striking examples here are the rainbows and sunsets. It is worth to apply to any of them a polarizer, colorful reflections can disappear completely or pobleknut.

Other recommendations

Filters for the camera are complex devices. But over time you can learn to work with them. "Polarik" can sometimes be used when it is necessary to increase the duration of exposure. Since it can reduce the transmitted light 4-8 times (2-3 steps), it can be used to shoot water and waterfalls.

If the polarizer is put on a wide-angle lens, it can create a catchy darkening of the edges of the picture ("vignetting"). To avoid this, you will certainly have to purchase a more "thin" expensive option.

Circular polarizers were created in order for the autofocus and camera metering systems to continue to operate with the filter on. Linear polarizers are much cheaper, but they can not be used with most digital SLR cameras (since they use phase autofocus and TTL - metering through the lens).