aperture /ap·er·ture/ (ap´er-cher) opening.
aperture
aperture,
piriform aperture the anterior end of the bony nasal opening, connecting the external nose with the skull.
ap·er·ture ( p  r-chr)n. 1. An opening, such as a hole, gap, or slit. 2. A usually adjustable opening in an optical instrument, such as a microscope, a camera, or a telescope, that limits the amount of light passing through a lens or onto a mirror. 3. The diameter of such an opening. 4. The diameter of the objective of a telescope or microscope. ap er·tur al adj. |
aperture
[ap′ərchər]
Etymology: L, apertura, an opening
an opening or hole in an object or anatomic structure.
aperture,
n an opening such as in bone.
aperture
an opening.
nasal aperture
the opening on the skull bounded by the nasal and incisive bones.
nasomaxillary aperture
the connecting aperture between the middle nasal meatus and the maxillary sinuses.
numerical aperture
measure of efficiency of a microscope objective proportional to the square root of the amount of light entering the instrument.
aperture
An opening, or the area of a lens, through which light can pass. See pupil.
angular aperture Half of the maximum plane subtended by a lens at the axial point of an object or image. (Sometimes the full plane angle is taken as the angular aperture but this is not convenient in optical calculations.) See sine condition.
aperture of a lenticular lens That portion of a lenticular lens which has the prescribed power (British Standard).
numerical aperture An expression designating the light-gathering power of microscope objectives. It is equal to the product of the index of refraction n of the object space and the sine of the angle u subtended by a radius of the entrance pupil at the axial point on the object, i.e. n sin u.
palpebral aperture The gap between the margins of the eyelids when the eye is open. An abnormal increase in the aperture occurs in some conditions, including Graves' disease, buphthalmos, Parinaud's syndrome and retrobulbar tumour. An abnormal decrease in the aperture occurs in some conditions, including ptosis, microphthalmos and ophthalmoplegia (Figs. A15 and A16). Syn. interpalpebral fissure (this term is more accurate although used infrequently); palpebral fissure. See exophthalmos.
aperture plane See aperture plane.
aperture ratio See relative aperture.
relative aperture The reciprocal of the f number. It is therefore equal to the ratio of the diameter of the entrance pupil to the primary focal length of an optical system. Syn. aperture ratio. Note: the definition of this term is not universally accepted; some authors define it as the reverse of the above. See antimongoloid slant; f number.
angular aperture Half of the maximum plane subtended by a lens at the axial point of an object or image. (Sometimes the full plane angle is taken as the angular aperture but this is not convenient in optical calculations.) See sine condition.
aperture of a lenticular lens That portion of a lenticular lens which has the prescribed power (British Standard).
numerical aperture An expression designating the light-gathering power of microscope objectives. It is equal to the product of the index of refraction n of the object space and the sine of the angle u subtended by a radius of the entrance pupil at the axial point on the object, i.e. n sin u.
palpebral aperture The gap between the margins of the eyelids when the eye is open. An abnormal increase in the aperture occurs in some conditions, including Graves' disease, buphthalmos, Parinaud's syndrome and retrobulbar tumour. An abnormal decrease in the aperture occurs in some conditions, including ptosis, microphthalmos and ophthalmoplegia (Figs. A15 and A16). Syn. interpalpebral fissure (this term is more accurate although used infrequently); palpebral fissure. See exophthalmos.
aperture plane See aperture plane.
aperture ratio See relative aperture.
relative aperture The reciprocal of the f number. It is therefore equal to the ratio of the diameter of the entrance pupil to the primary focal length of an optical system. Syn. aperture ratio. Note: the definition of this term is not universally accepted; some authors define it as the reverse of the above. See antimongoloid slant; f number.
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Fig. A15 Palpebral aperture PA and corneal apex CA
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Fig. A16 Average dimensions of the normal palpebral aperture of a Caucasian eye
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