Word Finder - lens

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An object, usually made of glass, that focuses or defocuses the light that passes through it.

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A device which focuses or defocuses electron beams.

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A convex shape bounded by two circular arcs, joined at their endpoints, the corresponding concave shape being a lune.

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A genus of the legume family; its bean.

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The transparent crystalline structure in the eye.

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(earth science) A body of rock, ice, or water shaped like a convex lens.

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A construct used in statically-typed functional programming languages to access nested data structures.

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(by extension) A way of looking, literally or figuratively, at something.

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To film, shoot.

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To become thinner towards the edges.

If not, the substitution of an achromatic lens will be of no advantage.

Its object is a practical one, to determine by scientific considerations the shape of lens best adapted to improve the capabilities of the telescope, which had been invented not long before.

Eyes are open invaginations without crystalline lens.

A, Early condition before the lens is deposited, showing the folding of the epidermic cell-layer into three.

On the surface of the carapace there are in both animals a pair of central eyes with simple lens and a pair of lateral eyetracts, which in Limulus consist of closely-aggregated simple eyes, forming a " compound" eye, whilst in Scorpio they present several AC separate small eyes.

The central eyes are " simple eyes," that is to say, have a single lens, and are hence called " monomeniscous."

Curiously enough, however, they differ from the cephalic Molluscan eye in the fact that, as in the vertebrate eye, the filaments of the optic nerve penetrate the retina, and are connected with the re surfaces of the nerve-end cells nearer the lens instead of with the opposite end.

The lateral eyes are in Limulus " compound eyes," that is to say, consist of many lenses placed close together; beneath each lens is a complex of protoplasmic cells, in which the optic nerve terminates.

Lateral eyes also may be present, arranged in lateral groups, and having a single or double cell-layer beneath the lens.

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

A similar argument may be applied to find at what point an achromatic lens becomes sensibly superior to a single one.

Calculation shows that, if the aperture be s in., an achromatic lens has no sensible advantage if the focal length be greater than about II in.

If we suppose the focal length to be 66 ft., a single lens is practically perfect up to an aperture of 1 .

If, further, on leaving the grating the light be received by a focusing lens, e.g.

In strictness this idea is appropriate only when the source is a luminous line, emitting cylindrical waves, such as might be obtained from a luminous point with the aid of a cylindrical lens.

The capital of the province was Arras, and the other important places were Saint-Omer, Bethune, Aire, Hesdin, Bapaume, Lens, Lillers, Saint-Pol and SaintVenant.

Flint glass particularly, which appeared quite satisfactory when viewed in small pieces, was found to be so far from homogeneous as to be useless for lens construction.

A crystal lens, turned on the lathe, was discovered by Layard at Nimrud along with glass vases bearing the name of Sargon; this will explain the excessive minuteness of some of the writing on the Assyrian tablets, and a lens may also have been used in the observation of the heavens.

Generally the mirror and lens are combined into a single piece of worked glass represented in section in fig.

The curved surfaces take the place of fl e the lens in fig.

The account is not very clear, but seems to imply the use of a concave mirror rather than a lens, which might be suggested by the word orbem.

The second edition, in which he in the same words discloses the use of a convex lens in the aperture as a secret he had intended to keep, was not published till 1589, thirty-one years after the first.

In this interval the use of the lens was discovered and clearly described by Daniello Barbaro, a Venetian noble, patriarch of Aquileia, in his work La Pratica della perspettiva (p. 192), published in 1568, or twenty-one years before Porta's mention of it.

The lens used by Barbaro was an ordinary convex or old man's spectacle-glass; concave, he says, will not do.

In the above argument the whole space between the object and the lens is supposed to be occupied by matter of one refractive index, and X represents the wave-length in this medium of the kind of light employed.

The function of a lens in forming an image is to compensate by its variable thickness the differences of phase which would otherwise exist between secondary waves arriving at the focal point from various parts of the aperture.

If we suppose the diameter of the lens to be given (2R), and its focal length f gradually to increase, the original differences of phase at the image of an infinitely distant luminous point diminish without limit.

But, as we have seen, such an error of phase causes no sensible deterioration in the definition; so that from this point onwards the lens is useless, as only improving an image already sensibly as perfect as the aperture admits of.

In observing the bands he received them at first upon a screen of finely ground glass, upon which a magnifying lens was focused; but it soon appeared that the ground glass could be dispensed with, the diffraction pattern being viewed in the same way as the image formed by the object-glass of a telescope is viewed through the eye-piece.

He shows how the paper must be moved till it is brought into the focus of the lens, the use of a diaphragm to make the image clearer, and also the application of the method for drawing in true perspective.

That Barbaro was really the first to apply the lens to the camera obscura is supported by Marius Bettinus in his Apiaria (1645), and by Kaspar Schott in his Magia Universalis (1657), the former taunting Porta with the appropriation.

In the Diversarum Speculationum Mathematicarum et Physicarum (1585), by the Venetian Giovanni Battista Benedetti, there is a letter in which he discusses the simple camera obscura and mentions the improvement some one had made in it by the use of a double convex lens in the aperture; he also says that the images could be made erect by reflection from any plane mirror.

Thus the use of the camera and of the lens with it was well known before Porta published his second edition of the Magia Naturalis in 1589.

These may be conveniently combined, as in Franklin glasses, where the upper half of the spectacle frame contains a weak lens, and the lower half, through which the eye looks when reading, a stronger one.

Airy, the astronomer, corrected his own astigmatism by means of a cylindrical lens.

In fact the uniformity of brass and bell-metal is only superficial; if we adopt the methods described in the article Metallography, and if, after polishing a plane face on a bit of gun-metal, we etch away the surface layer and examine the new surface with a lens or a microscope, we find a complex pattern of at least two materials.

It is desirable for two reasons that the image should lie in the plane of the paper, and this can be secured by placing a suitable lens between the object and the prism.

The word is also used as a unit of linear measurement of the magnifying power of a lens or microscope.

The width of each of the portions aghc and acfe cut away from the lens was made slightly greater than the focal length of lens X tangent of sun's greatest diameter.

In this instrument a considerable linear relative movement of the divided lens corresponds with a comparatively small separation of the double image, so that simple verniers reading to 6 1 0 in.

Ramsden's dioptric micrometer consists of a divided lens placed in the conjugate focus of the innermost lens of the erecting eye-tube of a terrestrial telescope.

This lens is divided and mounted like a heliometer objectglass; the separation of the lenses produces the required double image, and is measured by a screw.

The magnifying power is varied by changing the lens a for another in which p has a different value.

The magnifying power of the eye-piece is that of a single lens of focus = Jp.

It consists in the introduction by Simms of a fifth lens, but no satisfactory description has ever appeared.

It is essentially the same in principle as Amici's micrometer, except that the divided lens is an achromatic positive instead of a negative lens.

If Struve had employed a properly proportioned double circular diaphragm, fixed symmetrically with the axis of the telescope in front of the divided lens and turning with the micrometer, it is probable that his report on the instrument would have been still more favourable.

Thus if a horizontal slit is illuminated by an arc lamp, and the light - rendered parallel by a collimating lens - is transmitted through the sodium tube and focused on the vertical slit of a spectroscope, the effect of the sodium vapour is to produce its refraction spec trum vertically on the slit.

These filaments are so fine and are set so closely together that they appear to form a continuous membrane until examined with a lens.

Rudimentary cephalic eyes occur in the Mytilidae and in Avicula at the base of the first filament of the inner gill, each consisting of a I pigmented epithelial fossa containing a cuticular lens.