| 单词 | aperture |
| 释义 | aperture The effective diameter of a lens or mirror. The ratio of the effective diameter to the focal length is called the relative aperture , which is commonly known as the aperture, especially in photographic usage. The reciprocal of the relative aperture is called the focal ratio . The numerical value of the focal ratio is known as the f-number of a lens. For example, a camera lens with a 40 mm focal length and a 10 mm aperture has a relative aperture of 0.25 and a focal ratio of 4. Its f-number would be f/4, often written f4. The light-gathering power of a telescope depends on the area of the lens, i.e. it is related to the square of the aperture. However, the larger the relative aperture the greater the aberrations. In microscopy large-aperture objectives (corrected for aberrations) are preferred, since they reduce the blurring caused by diffraction of light waves |
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