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Visible light is composed of lights of various wavelengths. Gathering up all of these lights to a point is ideal for objective lenses.With a single lens, because light is bent in the same way as with a prism, the focal lengths of lights with different wavelengths vary. As a result, not all light rays reach the same point, which causes chromatic aberration.An achromatic lens made with conventional glass materials can match focal lengths of two different wavelengths. For red and blue colors, for example, that contain both ends of the wavelengths of visible light, chromatic aberration can be reduced to a certain extent by conforming their focal lengths. However, with more detailed examination, because light with other wavelengths such as green has different focal lengths, residual chromatic aberration results. This residual chromatic aberration is known as secondary spectrum.Combinations of conventional glasses cannot solve this secondary spectrum problem, but particular optical materials which have a unique characteristic of dispersion are needed.ED (Extra-low Dispersion) glass has this unique characteristic and when combined with other glasses minimizes the effects of the secondary spectrum. Comparing to achromatic lenses, ED glass reduces chromatic aberration to a remarkable degree.

More than 30 000 patients were infected with HIV or hepatitis C from drugs derived from the contaminated blood of prisoners and drug users. How was such tragedy allowed to happen?

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State Duma Deputy Nikolay Valuev is helping build the second branch of the Baikal-Amur Mainline (BAM) in the Russian Far East. Despite extreme conditions—temperatures dropping to -60°C in winter and soaring to +40°C in summer—this will become one of the longest railways in the world.

In the case of a lens fully compensated for coma aberration and astigmatism, the light rays coming from a point apart from the optical axis are focused at one point. But this point is not always included in the vertical plane to the optical axis. This is called Curvature of Field. With a lens having this aberration, even if you focus around the center of the field, the periphery of the field appears out of focus. It can cause very bad effects especially on wide-field-type binoculars.

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This is caused by the difference in distance of the incident light from the optical axis. While spherical aberration is caused by a difference in focused point, coma is caused by a difference in magnification. A point image such as a star tails toward the exterior like a comet, which "coma" refers to. Coma strongly influences image quality in the periphery of the field.

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Poor diet is more dangerous than smoking. It contributes to one in five deaths worldwide. How can countries avoid the looming food crisis? What food is truly harmful, and what is just believed to be damaging? Anna Chapman seeks the answers.

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Vladimir Soloviev investigates the assassination attempt on Donald Trump, one of the most high-profile attempts in US history. Discover more in the premiere, 'Bullet for the President'.

NATO bombings with depleted uranium shells have caused thousands of cancer deaths in the former Yugoslavia and Iraq. Why does NATO deny these deadly effects on civilians and continue to use radioactive weapons today?

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Nikon's binoculars have received high evaluation because of their excellent optical system. Nikon knows that a bright image and sharp details are the priority of binoculars, and makes utmost efforts to achieve this. Correcting lens aberration is vitally important.Nikon's binoculars are designed to correct the aberration described below properly to realize the brightest and sharpest image.

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Distortion is caused by variations in the magnification of the image depending on the distance from the optical axis. There are two types of distortion: positive and negative.This image distortion, irrespective of image visibility, increases in proportion to the incident angle cubed.

This film by Klim Poplavsky tells the story of the talented teenage writer Faina Savenkova from Donbass who writes plays and stories about children in her region and life under Ukrainian shelling. Her work in support of the children of Donbass has landed her on the Mirotvorets 'death list'.

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Scale, stunning natural scenery, talented actors in every village, and local stories at the heart of every script. How Yakutia became a giant movie set.

This is caused by a difference in light wavelength. The focal point or magnification of a lens varies according to the wavelength of each type of incident light. Therefore, if you look at an image through a lens with chromatic aberration, color fringing may occur.Because a single lens cannot compensate for chromatic aberration, two lenses of different optical characteristics are combined to correct this aberration.Nikon's original ED (Extra-low-Dispersion) glass lenses effectively compensate for color fringing.

A bundle of light rays coming from one point on the optical axis is focused at a different place than the focused point depending on the distance from the optical axis when the light incidents. This deviation is caused by variations in angles of each incident light ray, and is called spherical aberration.Suppose a screen is placed at P' in the illustration above, the image of P will not be a focused point, but a blurred circle. Making the lens diameter smaller reduces such spherical aberration.

The meridional plane (which contains the optical axis of the lens) and the sagittal plane (which is vertical to the meridional plane) have different radii. Therefore, the meridional and sagittal rays have different focal points. This is called an astigmatism aberration. When a latticepatterned object is viewed using a lens with an astigmatism, horizontal stripes appear in focus and vertical stripes appear out of focus. Conversely, when horizontal stripes appear out of focus, vertical stripes are in focus. Since astigmatism increases in proportion to the incident angle squared, astigmatism greatly influences image quality at the peripheral area of binoculars with a wide field of view.

A former SBU colonel is investigating the «Russian Volunteer Corps.» Why are Ukrainian soldiers and foreign mercenaries involved? What are the group's objectives and what is its true nature?