| Added | Wed, 19/10/2016 |
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Aberration of optical system — error or error image in the optical system caused by deviation of the beam from the direction in which he would have to go in a perfect optical system.
Aberrations can be divided into diffraction, chromatic (colored) and also monochromatic, that is inherent to monochromatic beams of rays. These include:
- spherical aberration
- coma
- astigmatism
- curvature of field (surface) image
- distortion
Spherical aberration of the lens due to the fact that its refractive surface to meet the individual rays in different angles of the light source becomes a ring.
Coma is manifested in the fact that every part of the optical system produces an image of a luminous point as a ring. The centers of the rings are not the same, resulting in their superposition, that is, the image of the point given by the system as a whole becomes unbalanced spots scattering.
Astigmatism occurs because the oblique rays of the beam have different points of convergence. In the pictures it looks like a blur point. At the same time luminous point located at the main optical axis, is transmitted as a point, but if the point is outside this axis, as dimming, crossed lines, etc. This phenomenon is most frequently observed at the edges of the image.
The image field curvature causes uneven sharpness across the image.
The distortion is manifested in the curvature and distortion of the geometry of the image. Distinguish between negative (barrel) and positive (pincushion).
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Chromatic aberration. It is caused by dispersion (decomposition of the beam into components of the spectrum) of the light passing through the lens. Different wavelength of each beam is responsible for different color, they are refracted at different angles and the result is a rainbow.
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A spherical aberration. The edges of the lens focal length is somewhat shorter than in the center, so the parallel light rays are refracted when passing through the spherical lens different rays, which pass through the edge of the lens, at the focal point of merge closer to the lens than those which pass through the center of the lens.
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"Coma" or somaticheskoe aberration. Their essence lies in the blurring of light sources located away from the center of the image instead of dots produce elongated spots of various shape.
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Coma in the photo. The image of a luminous point on the edges of the frame is obtained in the form of a "flying comet" and not in the form of a point
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When the larger star in a telescope looks like a small circle (circle Erie), to which the concentric light rings of light, whose brightness falls off rapidly from the center to the edges. This is due to the wave nature of light, namely, diffraction. The essence of the phenomenon can be understood by the following picture, here graphically depicts the gradient of the distribution of energy in the circle Erie and gradually evanescent diffraction rings around it.
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Blurred image of the star is not concentric circular shape, but instead more like a square, or a triangle means that the mirror of the telescope is strongly clamped in the frame.
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Coma for old photos
60-e years Moscow (Russia)
Photographer: Tadeusz Sail.
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