CPL filter with circular polarization. photography lessons

2024 Author: Sierra Becker | [email protected]. Last modified: 2024-02-26 03:46

What is a CPL polarizing filter? This is a valuable accessory that any photographer should have in their bag. How does a polarizer affect an image? In order to develop an intuition about this point, it is often necessary to experiment for a long time. In this article, you will learn how to speed up this process, how and how this product can make the task easier (and sometimes harmful) in different situations.

Where is the CPL filter attached? It is always in front of the front lens of the objective. How does this device work? It filters direct reflections of sunlight at certain angles. This is useful, as other light is often richer in hue and more diffuse. Working with this device also requires increasing shutter speed (because some beams are deflected). The filtration angle is controlled by rotating the device. From finding the camera's line of sight relative to the sundepends on the strength of the effect.

Filter rotation

When can I get the maximum effect with the CPL filter? Only if the camera's line of sight is perpendicular to the sunlight. You can imagine this by pointing your index finger at the sun, while placing your thumb at a right angle to it. As you rotate your hand to point toward the sun, whatever course your thumb points to will determine the line of highest polarizer effect.

However, the fact that the CPL filter will provide the best result in these directions does not necessarily mean that it will be most noticeable in them. The limiting polarization will appear during its rotation, which will change the angle relative to the daylight. The best way to get a feel for how the filter works is to rotate it while looking at the camera display or viewfinder.

Using a wide-angle lens may result in poor results because the polarizing effect varies with 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, and on the other side, it will be visible.

Clearly, wide-angle lenses are not perfect. However, the turns of the "polar" can sometimes make the effect more vital. Very often, professionals place the most pronounced polarization action closer to the edge or corner of the picture.

Description

Photographers use two types of filters to create high-quality images: withlinear polarization and circular. These devices isolate and isolate areas rich in polarized reflected light. With their help, when shooting the bottom, you can filter out bright glare, or capture the landscape outside the window without your 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 rays modified in a circle. They turn any refraction of rays into a spherical one. In fact, the circular "polarizer" does not interfere with autofocus, allows you to correctly guess the exposure and can be installed on all cameras (including old ones).

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

Circular filters are more difficult than others, so they cost more. On the outside of this device there is a conventional linear device, and on the inside - a quarter-wave plate that turns linear polarization into spherical.

Photo

Polarizing filters for the camera are devices designed to eliminate unwanted effects (reflections, glare), reduce the brightness (with a parallel increase in saturation) of the sky and otherobjects to achieve aesthetic goals. They look like ordinary filters, but have front and back parts of equal thickness that can rotate freely.

How is the CPL filter applied? What is this device for? Its back is screwed to the lens, and the desired effect is selected by turning the front half to any angle. The front segment can be equipped with an internal thread, with which an objective cap, threaded hood or other filters are attached, which is an irrefutable plus.

Different segments of reflective objects can give a reflection with different polarization angles, which cannot be suppressed synchronously by one 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, except for the rear, must be linearly polarized. This is necessary because the optical compensator placed in the circular filter prevents other devices that may be placed behind it from achieving the effect.

What else is a polarizing lens filter famous for? Its optical density is usually located in the range from two to five. Color distortion may occur. In general, some devices have a drop of up to one stop in the purple-blue region, which causes the picture to turn out with a green tint. Cheap devices can disgustingly reproduce small details. "Polyarik", along with a "protective" UV-blocking filter, isthe most exploited 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 with linear dichroism. This detail is a kind of layer of acetyl cellulose containing an impressive number of the smallest microliths of herapatite (the iodide compound of quinine sulfate).

Such polyvinyl-iodine films with polymer chains synchronously oriented are used. The orientation of the microlites is identical due to the electric field, and the polymer chains are guided by mechanical tension. The circular filter is also equipped with an optical compensator - a quarter-wave phase plate. With this part, you can determine the difference in the path of the two launches of the beams. It works according to the phenomenon of double refraction of light in crystals.

Transformation of light

The simple beam and the exceptional beam have different speeds. Their optical path lengths are also not the same. Therefore, they acquire a travel difference, measured by the thickness of the crystal through which they pass. It is installed along the path of the 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 linearly polarized beams into circularly polarized light (and vice versa), increasing the path difference to 90 degrees. With such features, all "polars" are made. The difference in both price and quality is due toadditional layers: protective, anti-reflective, water-repellent.

Appearance

When was the polarizing filter for the lens developed? This product was born from the development of TTL camera automation elements, which, unlike photographic materials, became dependent on innovative exposure to light.

In general, linear polarization radiation makes metering difficult and in SLR cameras partially interferes with the operation of automatic phase focusing.

In astronomy, "polarizers" are part of devices that 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 strength of the magnetic field in areas of radiation generation, say, on white dwarfs.

Nikon CPL

The Nikon 52 mm CPL polarizing filter is a valuable item for the landscape photographer and for those who like to get high-quality pictures. There are at least six reasons why you should buy this product:

• For photographing water (it becomes darker and more transparent).
• Shooting a landscape (the "saturation" of greenery and sky increases).
• For shooting at an angle through a window (to eliminate glare and reflections from the glass).
• Elimination of reflections on a sunny day (from water, glass, car).
• Increase shutter speed by a couple of stops (when needed).
• Lens protection againstmechanical impact.

Buy this filter for those who go to travel to warm countries - this is an indispensable assistant in making colorful photos. In bright sunlight, this device improves image quality by increasing contrast and saturation while eliminating haze.

Restrictions

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, you need to select the desired degree of polarization, which will allow you to eliminate glare from water or glass when shooting, as well as get more fluffy and white clouds, a saturated sky.

There are some restrictions on the use of such devices:

• When 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 will reset the image to its original state.
• Polars soften the amount of light entering the camera's sensor through the lens, so professionals often increase the exposure balance by 1-2 stops.

Flaws

Photography lessons are essential for beginner photographers to create high-quality pictures. We have found that polarizers are very useful. Unfortunately, they have the following drawbacks:

• Because of this device, the exposure may ask for more light in 4-8times (2-3 steps) than usual.
• They need a certain angle to the sun to get the best results.
• These filters make it hard to navigate the camera viewfinder.
• These are some of the more expensive appliances.
• They require rotation, so may increase composition time.
• Usually not available for wide-angle and panorama shots.
• If the filter is dirty, it may reduce the picture quality.

Moreover, sometimes reflections are needed in a photo. The most striking examples here are rainbows and sunsets. If you apply a polarizer to any of them, colorful reflections may disappear completely or fade.

Other recommendations

Camera filters 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 exposure time. Since it can cut 4-8 times (2-3 stops) the transmitted light, it can capture water and waterfalls.

If you put a polarizer on a wide-angle lens, it can create a bright 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 designed to keep the camera's autofocus and metering systems working while the filter was on. Linear "polars" are much cheaper, but they cannot be used with most digital SLR cameras (as they use phase detection autofocus and TTL - meteringthrough the lens).