aperture

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aperture

 [ap´er-chur]
inferior aperture of minor pelvis (inferior aperture of pelvis) pelvic outlet.
numerical aperture an expression of the measure of efficiency of a microscope objective.
superior aperture of minor pelvis (superior aperture of pelvis) pelvic inlet.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

ap·er·ture

(ap'er-chūr),
1. Opening. An inlet or entrance to a cavity or channel. In anatomy, a gap or hole.
See also: fossa, ostium, orifice, pore. Synonym(s): apertura [TA]
2. The diameter of the objective of a microscope.
Synonym(s): aditus [TA]
[L. apertura, an opening]
Farlex Partner Medical Dictionary © Farlex 2012

ap·er·ture

(ap'ĕr-chŭr) [TA]
1. An inlet or entrance to a cavity or channel; in anatomy, an open gap or hole.
2. The diameter of the objective of a microscope.
Synonym(s): aditus [TA] , apertura [TA] .
[L. apertura, an opening]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012

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.
Fig. A15 Palpebral aperture PA and corneal apex CAenlarge picture
Fig. A15 Palpebral aperture PA and corneal apex CA
Fig. A16 Average dimensions of the normal palpebral aperture of a Caucasian eyeenlarge picture
Fig. A16 Average dimensions of the normal palpebral aperture of a Caucasian eye
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann

ap·er·ture

(ap'ĕr-chŭr) [TA]
1. [TA] Opening. An inlet or entrance to a cavity or channel. In anatomy, a gap or hole.
Synonym(s): apertura.
2. The diameter of the objective of a microscope.
See also: fossa, ostium, orifice
Synonym(s): aditus [TA] .
[L. apertura, an opening]
Medical Dictionary for the Dental Professions © Farlex 2012
References in periodicals archive ?
To record as much comet in as short a time as possible requires the largest lens aperture (smallest f/number) available.
With the camera on a tripod you can maximise the number of exposure options and stop down your lens aperture for greater depth of field, no matter how slow the shutter speed.
The lens aperture ranges from f/2.9 to f/16, and is compatible with Canon's EF mount and Nikon's F mount cameras, and a lot of other digital cameras with the use of mount adapters.
To reduce exposure time, select the maximum lens aperture and use a moderately fast ISO setting of 1600 or 3200--today's cameras have much improved resolution at higher ISO settings than in the past.
Unlike, a macro lens, an ultra wide-angle produces much greater depth of field, particularly when using a small lens aperture. But isolating a single plant or bloom in the frame requires a totally different approach and this is where the macro lens comes into its own.
Best practice entails shooting at the maximum lens aperture and setting an ISO rating that will allow you to maintain a minimum shutter speed of at least 1/250 of a second, preferably faster.
Setting the camera to aperture-priority mode and choosing the maximum lens aperture will result in the fastest shutter speed being selected for a correct exposure.
Forget the tripod--it's essential for macro studies of wildflowers and insects, enabling you to stop down your lens aperture for maximum depth of field no matter how slow the resulting shutter speed
It will give you so many more options and ensure you can stop down your lens aperture for maximum depth of field no matter how slow the resulting shutter speed