Word Finder - aperture

definition

An opening, gap, or hole, usually small and narrow

example

an aperture in a wall

definition

Something which restricts the diameter of the light path through one plane in an optical system.

definition

The diameter of the aperture (in the sense above) which restricts the width of the light path through the whole system. For a telescope, this is the diameter of the objective lens.

example

This telescope has a 100cm aperture.

definition

(communications) The (typically) large-diameter antenna used for receiving and transmitting radio frequency energy containing the data used in communication satellites, especially in the geostationary belt. For a comsat, this is typically a large reflective dish antenna; sometimes called an array.

definition

(of a right circular cone) The maximum angle between the two generatrices.

example

If the generatrix makes an angle θ to the axis, then the aperture is 2θ.

From far away, the opening of the cave looked like a mere aperture in the rock wall.

The small aperture in the wall let in enough of the outside light to create shadows all around the room.

After taking the camera back to the store, they determined that the damage was in the aperture.

Compatible only with Mac OS X and being somewhat reminiscent of the operating system's iPhoto application, Aperture 3 is an excellent tool for organizing photos into libraries and projects.

The outer wall of the capsule is incomplete at one pole, leaving an aperture through which the thread is discharged.

At the front is a large slab, sometimes carved, with a small aperture in it, through which offerings might be inserted.

The nest is an inch and more in diameter, with a small aperture for an entrance.

It is necessary that the aperture of the pupil be accommodated to the angular extent of the spectrum, or reciprocally.

If a distal pore or aperture is present, it is excretory in function; suck varieties have been termed " cystons " by Haeckel.

The former are for the most part concerned with questions relating to the theory of light, arising out of his professorial lectures, among which may be specially mentioned his paper "On the Diffraction of an Object-Glass with Circular Aperture."

J Right (archaic left) nephri dium's aperture.

If an aperture for ingress and egress, for purposes of feeding, were left in the wall of such a chamber, there would arise in a rudimentary form what is known as the tubular nest or web; and the next important step was possibly the adoption of such a nest as a permanent abode for the spider., Some spiders, like the Drassidae and Salticidae, have not advanced beyond this stage in architectural industry; but next to the cocoon this simple tubular retreat - whether spun in a crevice or burrow or simply attached to the lower side of a stone - is the most constant feature to be observed in the spinning habits of spiders.

In both there are species which form no nest or burrow, others which construct a simple silk-lined tunnel in the soil, and others which close the aperture of the burrow with a hinged door; while both share the habit of lining the burrow with silk to prevent the infall of loose sand or mould; and the species which make an open burrow close the aperture with a sheet of silk in the winter during hibernation and open it again in the spring.

Be that as it may, the snare in many instances, as in that of the Agalenidae (Tegenaria, Agalena), a family closely allied to the Lycosidae, is a horizontal sheet of webbing, upon which the spider runs, continuous with the lower half of the aperture of the tube, of which it is simply an extension.

When a current is passed through the wire forming the coil, the fragment of iron is drawn more into the aperture of the coil where the field is stronger and so displaces an index needle over a scale.

The shell of Clausilia is sinistral and its aperture is provided with a hinged plate.

In the Auriculidae the aperture is denticulated.

The pseudo-deltidium (so named by Bronn in 1862) is a single plate which grows from the apex of the delthyrium downwards, and may completely close the aperture.

By the crushing action of their pincers, and an alternate backward and forward movement, they bring the soft blood-holding tissues of the victim close to the minute pin-hole aperture which is the scorpion's mouth.

The sperm is removed by the male from the genital aperture into a special receptacle on the terminal segment P FIG.

Thus held out at some distance from the body, it is cautiously advanced by the male spider to the genital aperture of the female.

A movable membranous j oint between the prosoma and the opisthosoma, the generative aperture opening upon the ventral side of the membrane.

Opisthosoma confluent throughout its breadth with the prosoma, with the dorsal plate of which its anterior tergal plates are more or less fused; at most ten opisthosomatic somites traceable; the generative aperture thrust far forwards between the basal segments of the 6th appendages.

When light passes through a small circular or annular aperture, the illumination at any point along the axis depends upon the precise relation between the aperture and the distance from it at which the point is taken.

If, as in the last paragraph, we imagine a system of zones to be drawn commencing from the inner circular boundary of the aperture, the question turns upon the manner in which the series terminates at the outer boundary.

If the aperture be such as to fit exactly an integral number of zones, the aggregate effect may be regarded as the half of those due to the first and last zones.

The amplitude of the light at any point in the axis, when plane waves are incident perpendicularly upon an annular aperture, is, as above, cos k(at-r 1)-cos k(at-r 2) =2 sin kat sin k(r1-r2), r2, r i being the distances of the outer and inner boundaries from the point in question.

The incident waves are thus plane, and are limited to a plane aperture coincident with a wave-front.

In experiment under ordinary circumstances it makes no difference whether the collecting lens is in front of or behind the diffracting aperture.

If the wave-length remains unchanged, similar effects are produced by an increase in the scale of the aperture.

We will now apply the integrals (2) to the case of a rectangular aperture of width a parallel to x and of width b parallel to y.

We readily find (with substitution for k of 27r/X) a2b S n J s in fl „2a2E2 „2b2n2 f2X2 f2X2 as representing the distribution of light in the image of a mathematical point when the aperture is rectangular, as is often the case in spectroscopes.

If the aperture be increased, not only is the total brightness over the focal plane increased with it, but there is also a concentration of the diffraction pattern.

The contraction of the diffraction pattern with increase of aperture is of fundamental importance in connexion with the resolving power of optical instruments.

This indefiniteness of images is sometimes said to be due to diffraction by the edge of the aperture, and proposals have even been made for curing it by causing the transition between the interrupted and transmitted parts of the primary wave to be less abrupt.

At the focal point (E =o, n = o) all the secondary waves agree in phase, and the intensity is easily expressed, whatever be the form of the aperture.

From the general formula (2), if A be the area of aperture, 102 = A2 / x2 f (7) The formation of a sharp image of the radiant point requires that the illumination become insignificant when, n attain small values, and this insignificance can only arise as a consequence of discrepancies of phase among the secondary waves from various parts of the aperture.

In the particular case of a rectangular aperture the course of things can be readily followed, especially if we conceive f to be infinite.

In the direction (suppose horizontal) for which n=o, /f=sin 0, the phases of the secondary waves range over a complete period when sin 0 =X/a, and, since all parts of the horizontal aperture are equally effective, there is in this direction a complete compensation and consequent absence of illumination.

The reason of the augmentation of resolving power with aperture will now be evident.

The larger the aperture the smaller are the angles through which it is necessary to deviate from the principal direction in order to bring in specified discrepancies of phase - the more concentrated is the image.

The definition of a fine vertical line, and consequently the resolving power for contiguous vertical lines, is thus independent of the vertical aperture of the instrument, a law of great importance in the theory of the spectroscope.

We conclude that a double line cannot be fairly resolved unless its components subtend an angle exceeding that subtended by the wave-length of light at a distance equal to the horizontal aperture.

If the angle subtended by the components of a double line be twice that subtended by the wave-length at a distance equal to the horizontal aperture, the central bands are just clear of one another, and there is a line of absolute blackness in the middle of the combined images.

The resolving power of a telescope with circular or rectangular aperture is easily investigated experimentally.

Merely to show the dependence of resolving power on aperture it is not necessary to use a telescope at all.

The (8), A function of the telescope is in fact to allow the use of a wider, and therefore more easily measurable, aperture.

Since the limitation of the width of the central band in the image of a luminous line depends upon discrepancies of phase among the secondary waves, and since the discrepancy is greatest for the waves which come from the edges of the aperture, the question arises how far the operation of the central parts of the aperture is advantageous.

Theory and experiment alike prove that a double line, of which the components are equally strong, is better resolved when, for example, one-sixth of the horizontal aperture is blocked off by a central screen; or the rays quite at the centre may be allowed to pass, while others a little farther removed are blocked off.

It has already been suggested that the principle of energy requires that the general expression for I 2 in (2) when integrated over the whole of the plane, n should be equal to A, where A is the area of the aperture.