What exactly does the PL eyepiece of astronomical telescope mean? Where's the good news? Is there a comparison?

Linear polarization scale is also called ordinary polarizer, and its English symbols are L-PL (unpolarizer) or polarization, filter——Linear), PlLineat, PL and POL.

The linear polarizer is gray in appearance, which can let the vibration light waves parallel to its polarization direction pass through, and at the same time can weaken the vibration light waves in other directions to varying degrees. Artificial linear polarizers are usually made of polyvinyl alcohol film, which has been impregnated with iodine and glued between two flat optical glasses. It can pass about 80% of linearly polarized light with the same polarization direction and less than 1% of linearly polarized light vibrating perpendicular to its polarization direction. Some filter manufacturers (such as Kenco and B-W) produce polarizers with larger sizes in order to be installed on the front and back of the subject to capture the photoelastic effect, or in front of the light source to eliminate the reflection on the surface of metal objects. For example, a 30×40cm polarizer provided by Kenco Company of Japan.

Polarizers are obviously different from ordinary color filters in black-and-white photography. Generally speaking, when the polarizer is converted into achromatic color, it will not change the contrast between different unpolarized colors and the contrast between black and white tones in the shooting scene, that is, it treats all unpolarized colors equally. Color filter can obviously change the contrast between different colors in the scene and the contrast between black and white in the picture through its different characteristics of light transmission and light blocking (transmission and absorption). '

Polarizers are also obviously different from color temperature adjustment filters and color compensation filters used in color photography. The polarizer does not change the color temperature of the light source, and generally does not affect the overall tone of the image formed by various unpolarized colors in the scene.

In order to eliminate or weaken the polarized light reflected by the photographed scene, the adjusting ring of the linear polarizer should be properly rotated so that the polarization direction and the vibration direction of the polarized light are perpendicular or inclined to each other. The closer the angle between them is to zero, the smaller the degree of polarization weakening, and the closer the angle between them is to 90 degrees. The greater the attenuation of polarized light.

The specific adjustment method is as follows: directly install the polarizer at the front end of the photographic lens of a single-lens framing camera or video camera, observe the polarized light source in the photographed scene through the framing focusing screen, and slowly rotate the adjusting ring of the polarizer until it disappears or weakens to the expected effect; Put the polarizer in front of your eyes, and rotate the adjusting ring of the polarizer while taking photos until the polarized light disappears or weakens to the expected size. Then, under the premise that the orientation of the adjusting ring is unchanged (that is, the direction indicated by the mark on the adjusting ring is unchanged), the polarizer is translated to the front end of the photographic lens of the paraxial camera. After that, the camera should not change the shooting orientation at will, otherwise the polarization direction of the polarizer needs to be readjusted.

In order to adjust the polarization direction of the polarizer, some manufacturers specially installed a small handle on the polarizer, and the direction of the handle is the polarization direction of the polarizer. Some manufacturers also carve a score line on the polarizer ring, and the diameter line passing through the score line is the polarization direction of the polarizer.

In order to facilitate cinematographers to shoot outdoors with B-type color film, some manufacturers produce composite polarizers. For example, Tiffany's 85BPOl and 85POI'' filters are composed of 85B and 85 warm color temperature filters and polarizer POl respectively. Another example is Japan's Baogu brand warm-tone polarizer (850 POL) and Japan's Kenco brand red polarizer (PR-60). German brand B 10 W WarmTonePolarizer.

The English symbol of circular polarizer is C—PL(CircularP0 1arizer) or PL-C. Common circular polarizers are Toshiba C-PL circular polarizer (exposure compensation 1 12), Gao Jian P0 1aCir circular polarizer, Kenke PL circular polarizer, etc. HAMA brand circular polarizers No.725 and No.726 (P 01Arizing filter-circular, the latter is a multilayer coated lens).

Circular polarizer is a kind of polarizer which can not only produce circularly polarized light (when used in the forward direction) but also test circularly polarized light (when used in the reverse direction). The appearance of the circular polarizer is also gray. A circular polarizer is formed by bonding a linear polarizer and quarter-wave plate (a special birefringent material). The optical axis of quarter-wave plate makes an angle of 45 with the vibration direction of polarized light of linear polarizer. Angle. Light enters from one end of the linear polarizer in the forward direction and from one end of the quarter-wave plate in the reverse direction.

The natural light incident on the circular polarizer in the forward direction becomes circularly polarized light after passing through the linear polarizer and quarter-wave plate (see figure1-12). According to the polarization direction of the linear polarizer, it forms an angle of 45 with the quarter-wave plate optical axis. Different relative orientations at the included angle can produce right-handed circularly polarized light or left-handed circularly polarized light.

Regardless of the position of the rotating circular polarizer, left-handed circularly polarized light cannot pass through the right-handed circular polarizer in reverse, and vice versa. According to this characteristic of circular polarizer, natural light and circularly polarized light can be tested: if a light can pass through both right-handed circular polarizer and left-handed circular polarizer in reverse, it is natural light. If a ray of light can reversely pass through a right-handed (or left-handed) circular polarizer, but cannot reversely pass through a left-handed (or right-handed) circular polarizer, it is right-handed (left-handed) circularly polarized light.

Right-handed circularly polarized light can be converted into left-handed circularly polarized light after passing through a half-wave plate, and vice versa. A circular polarizer can produce circularly polarized light, and the circularly polarized light is not affected by the beam splitter that will pass through it. The circular polarizer of linear polarizer has all the above characteristics.

Color polarizer is a unique composite polarizer, which can continuously change the color of the shooting scene and belongs to special effect filter.