Lens sentence example
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.
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.Advertisement
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."
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.Advertisement
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 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.Advertisement
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.Advertisement
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.Advertisement
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.
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.Advertisement
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.Advertisement
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.Advertisement
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.Advertisement
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.
He also said that there were several barracuda who would be attracted to the shiny lens on my camera.
The doctor aims the laser exactly onto the posterior lens capsule in order to cut away a small circle shaped area.
The latter is determined by the lens aperture, CCD integration time, and the sensitivity of the silicon CCD detector.Advertisement
The use of the convex lens, which is given as a great secret, in place of the concave speculum of the first edition, is not so clearly described as by Barbaro; the addition of the concave speculum is proposed for making the images larger and clearer, and also for making them erect, but no details are given.
In his later book, Dioptrice (1611), he fully discusses refraction and the use of lenses, showing the action of the double convex lens in the camera obscura, with the principles which regulate its use and the reason of the reversal of the image.
He also demonstrates how enlarged images can be produced and projected on paper by using a concave lens at a suitable distance behind the convex, as in modern telephotographic lenses.
Wotton written to Lord Bacon in 1620 we learn that Kepler had made himself a portable dark tent fitted with a telescope lens and used for sketching landscapes.
They do not seem to have used a lens, or thought of using the telescope for projecting an enlarged image on Kepler's principle.
This was done in 1612 by Christoph Scheiner, who fully described his method of solar observation in the Rosa Ursina (1630), demonstrating very clearly and practically the advantages and disadvantages of using the camera, without a lens, with a single convex lens, and with a telescopic combination of convex object-glass and concave enlarging lens, the last arrangement being mounted with an adjustable screen or tablet on an equatorial stand.
Robert Boyle seems to have been the first to construct a box camera with lens for viewing landscapes.
At one end of it paper was stretched, and at the other a convex lens was fitted in a hole, the image being viewed through an aperture at the top of the box.
If the objects could not be inverted, another lens was used for erecting the images.
One was a wooden box with a projecting tube in which a combination of a concave with a convex lens was fitted, for throwing an enlarged image upon the focusing screen, which in its proportions and application is very similar to our modern telephotographic objectives.
He has fully discussed the optical theory of the dark chamber, with and without a lens, and its analogy to the eye.
Sir Isaac Newton, in his Opticks (1704), explains the principle of the camera obscura with single convex lens and its analogy with vision in illustration of his seventh axiom, which aptly embodies the correct solution of Aristotle's old problem.
These prisms may be combined with concave lenses, which correct the myopia, or, since a concave lens may be considered as composed of two prisms united at their apices, the same effect may be obtained by making the distance between the centres of the concave lenses greater than that between the centres of the pupils.
Owing principally to differences in the length of the inch in various countries this method had great inconveniences, and now the unit is the refractive power of a lens whose focal length is one metre.
A lens of twice its strength has a refractive power of 2 D, and a focal length of half a metre, and so on.
He then altered the magnifying power by sliding the field lens of the eye-piece (which was fitted with a slipping tube for the purpose) along the eye-tube, till the images were brought into contact.
Poetsch in 1883, and originally applied to shafts passing through quicksands above brown coal seams, has been applied with advantage in opening new pits through the secondary and tertiary strata above the coal measures in the north of France and Belgium, some of the most successful examples being those at Lens, Anzin and Vicq, in the north of France basin.
In 1677 he described and illustrated the spermatozoa in dogs and other animals, though in this discovery Stephen Hamm had anticipated him by a few months; and he investigated the structure of the teeth, crystalline lens, muscle, &c. In 1680 he noticed that yeast consists of minute globular particles, and he described the different structure of the stem in monocotyledonous and dicotyledonous plants.
On the other hand, to produce convergence with water or hydrogen gas, in both which the velocity of sound exceeds its rate in air, the lens ought to be concave.
One eye-space i s shown lens, and its three pigmentabove on the left.
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.
This roused the jealousy of the United Provinces, and they made a separate peace with Spain in January 1648; but the valour of the French generals made the skill of the Spanish diplomatists of no avail, for Turenne's victory at Zusmarshausen, and Conde's at Lens, caused the peace of Westphalia to be definitely signed in October 1648.
The Five-foot Spectroheliograph of the Mount Wilson Solar Observatory (camera lens, camera slit and plate carrier in section).
The slit of the collimator confines the light to a nearly linear source, the beam diverging from each point of the source being subsequently made parallel by means of a lens.
The lens may then be also dispensed with, and the whole collimator becomes unnecessary if the luminous source is narrow and at a great distance, as for instance in the case of the crescent of the sun near the second and third contact of a total solar eclipse.
These conditions may be generally satisfied by projecting the image of the source on the slit with a lens of sufficient aperture.
When the slit is narrow light is lost through diffraction unless the angular aperture of this condensing lens, as viewed from the slit, is considerably greater than that of the collimator lens.
The collimator of a spectroscope should be detached, or moved so as to admit of the introduction of an auxiliary slit at a distance from the collimator lens equal to its focal length.
In order to record line spectra it is by no means necessary that the receiving instrument (bolometer or radiometer) should be linear in shape, for the separation of adjacent lines may be obtained if the linear receiver be replaced by a narrow slit in a screen placed at the focus of the condensing lens.
At the other end of the collimator there is a condensing lens for bringing the rays into parallelism.
A different arrangement, used in the instrument described below, consists in having the magnet hollow, with a small scale engraved on glass firmly attached at one end, while to the other end is attached a lens, so chosen that the scale is at its principal focus.
In this case the geometrical axis is the line joining the central division of the scale to the optical centre of the lens.
The position of the magnet is observed by means of a small telescope, and since the scale is at the principal focus of the lens, the scale will be in focus when the telescope is adjusted to observe a distant object.
When the periscope is not in use, the prism is lowered and protects the upper lens in the body.
The two achromatic lenses, C and D, bring the rays to a focus on the plane surface of the large lens, E, forming an image there.
From the large lens, E, the rays pass through the open air for a considerable distance, depending upon how much the mast has been raised, to the lower optical system.
By moving the lens G up and down the image can be formed in the correct position for the eyepiece at all extensions of the mast.
An optical tube replaced this cupola in the "Gustave Zede," and comprised a short tube (on top of the submarine) with a lens to close the top end, which was kept just above the surface when running submerged.
The stipules are sometimes so minute as to be scarcely distinguishable without the aid of a lens, and so fugacious as to be visible only in the very young state of the leaf.
The movements of the apparatus, which when complete should consist of two similar pendulums in planes at right angles to each other, are recorded by means of a beam of light, which, after reflection from the mirror or mirrors, passes through a cylindrical lens and is focussed upon a moving surface of photographic paper.
In the first it is a biconvex lens, from which segments are continually cut off parallel to the posterior surface; and in the second an elongated dome, from which segments are cut off by a transverse wall.
The common story is that Lippershey, happening one day, whilst holding a spectacle-lens in either hand, to direct them towards the steeple of a neighbouring church, was astonished, on looking through the nearer lens, to find that the weathercock appeared nearer and more distinct.
All the original Dutch telescopes were composed of a convex and a concave lens, and telescopes so constructed do not invert.
In his Saggiatore Galileo states that he solved the problem of the construction of a telescope the first night after his return to Padua from Venice, and made his first telescope next day by fitting a convex lens in one extremity of a.
The lens of the human eye is not achromatic.
The triple object-glass, consisting of a combination of two convex lenses of crown glass with a concave flint lens between them, was introduced in 1765 by Peter, son of John Dollond, and many excellent telescopes of this kind were made by him.
These, falling in turn on the lens of the human eye, are converged by it and form an image on the retina.
It is possible to construct a triple objective of two positive lenses enclosing between them one negative lens, the two former being made of the same glass.
Hence it is clear that if the two positive lenses of equal curvature power of o 60 and 0.102 respectively are combined with a negative lens of light flint o 569, then a triple objective, having no secondary spectrum (at any rate with respect to the blue rays), may be obtained.
But while an achromatic combination of o 60 and 0.102 alone will yield an objective whose focal length is only 1.28 times the focal length of the negative or extra dense flint lens, the triple combination will be found to yield an objective whose focal length is 73 times as great as the focal length of the negative light flint lens.
This case well illustrates the much closer approach to strict rationality of dispersion which is obtainable by using two different sorts of glass for the two positive lenses, even when one of them has a higher dispersive power than the glass used for the negative lens.
The front lens is made of baryta light flint glass 3.
The shape of the universe may thus be compared to that of a grindA stone or lens, the sun being situated about midway between the two surfaces.
If the source be a point, such as the image formed by a lens of small focus or by a fine hole in a plate held close to a bright flame, the outline of the shadow is to be found by drawing straight lines from the luminous point so as to envelop the opaque body.
To prevent this overlapping of images, and yet to admit a good deal of light, is one main object of the lens which usually forms part of the camera obscura.
Both mirrors are usually concave; if plane, a concave lens is placed immediately before them.
These images would be short lines of light; but a plano-cylindrical lens is placed with its axis horizontal just in front of the recording surface.
Between the concave spherical surfaces of those cups is placed a steel 0 ball, being either a complete sphere or a lens having convex surfaces of a somewhat less radius p i than the concave surfaces of the cups.
He investigated the optical constants of the eye, measured by his invention, the ophthalmometer, the radii of curvature of the crystalline lens for near and far vision, explained the mechanism of accommodation by which the eye can focus within certain limits, discussed the phenomena of colour vision, and gave a luminous account of the movements of the eyeballs so as to secure single vision with two eyes.
Matters are so arranged by giving a torsion to the wire carrying the aluminium disk F that for a certain potential difference between the plates H and G, the movable part F comes into a definite sighted position, which is observed by means of a small lens.
If this distance is varied until the attracted disk comes into a definite sighted position as seen by observing the end of the index through the lens, then since the force f is constant, being due to the torque applied by the wire for a definite angle of twist, it follows that the difference of potential of the two plates varies as their distance.
If there be refraction at a collective spherical surface, or through a thin positive lens, 0' 2 will lie in front of O' 1 so long as the angle u2 is greater than u 1 (" under correction "); and conversely with a dispersive surface or lenses (" over correction ").
In most cases, two thin lenses are combined, one of which has just so strong a positive aberration (" under-correction," vide supra) as the other a negative; the first must be a positive lens and the second a negative lens; the powers, however, may differ, so that the desired effect of the lens is maintained.
It is generally an advantage to secure a great refractive effect by several weaker than by one high-power lens.
A system is said to be " chromatically under-corrected " when it shows the same kind of chromatic error as a thin positive lens, otherwise it is said to be " over-corrected."
For example, it is possible, with one thick lens in air, to achromatize the position of a focal plane of the magnitude of the focal length.
For an achromatic dispersive lens the converse must be adopted.
Should the cemented system be positive, then the more powerful lens must be positive; and, according to (4),.
If its chromatic effect (d4/4) be greater than that of the same lens, this being made of the more dispersive of the two glasses employed, it is termed " hyper-chromatic."
The black variety of cochineal is sometimes sold for silver cochineal by shaking it with powdered talc or heavy-spar; but these adulterations can be readily detected by means of a lens.
If no one of these tensions is greater than the sum of the other two, the drop will assume the form of a lens, the angles which the upper and lower surfaces of the lens make with the free surface of A and with each other being equal to the external angles of the triangle of forces.
This drop will not spread out like the first drop, but will take the form of a flat lens with a distinct circular edge, showing that the surface-tension of what is still apparently pure water is now less than the sum of the tensions of the surfaces separating oil from air and water.
So far from spreading over the surface, as according to its lower surface-tension it ought to do, it remains suspended in the form of a lens.
This body appears to be the source of light, and has behind it a reflector formed of concentric lamellae, while, in front, in some cases, there is a refracting lens.
The system consequently acts as a continuous lens, magnifying the object in a vertical direction.
Then place a Lens of about three foot radius (suppose a broad Object-glass of a three foot Telescope), at the distance of about four or five foot from thence, through which all those colours may at once be transmitted, and made by its Refraction to convene at a further distance of about ten or twelve feet.
You may also see, that, if any of the Colours at the Lens be intercepted, the Whiteness will be changed into the other colours.
And therefore, that the composition of whiteness be perfect, care must be taken, that none of the colours fall besides the Lens."
This oil is largely used by microscopists in what is known as the "oil-immersion lens."
A simpler arrangement, also employed by Tyndall, is to cause the rays to be reflected outwards parallel to one another, and to concentrate them by means of a small flask, containing the iodine solution and used as a lens, placed some distance from the camera.
The essential difference between these two kinds of eye appears to be that the Chaetopod eye (in its higher developments) is a vesicle enclosing the lens, whereas the Arthropod eye is a pit or series of pits into which the heavy chitinous cuticle dips and enlarges knobwise as a lens.
The nerveend-cells, which lie below the lens, are part of the general epidermis.
More usually, by an infolding of the layer of cells in development, we get three layers under the lens; the front layer is the corneagen layer, and is separated by a membrane from the other two which, more or less, fuse and contain the nerve-end-cells (retinal layer).
Those nearest to the lens are the corneagen cells of this more elaborated eye, and those between the original retinula cells and the corneagen cells become firm and transparent.
B represents an intermediate hypothetical form in which the cells beneath the lens are beginning to be superimposed as corneagen, vitrella and retinula, instead of standing side by side in horizontal series.
Lateral eyes also are often present which are monostichous with aggregated lenses (Limulus)or with isolated lenses(Scorpio), or are diplostichous with simple lens (Pedipalpi, Araneae, &c.).
Fronde The victor of Lens and Charenton imagined that every of the one was under an obligation to him, and laid claim to a dictatorship so insupportable that Anne of Austria and Mazarin assured by Gondi of the concurrence of the parlement and peoplehad him arrested.
Of polarimeters for the study of rotary polarization there are three principal forms. In Wild's polaristrobometer, light from a soda flame, rendered parallel by a lens, is polarized by a Nicol's prism, and after traversing the space into which the active substance is to be inserted, falls on a Savart's plate placed in front of an astronomical telescope of low power, that contains in its eyepiece a Nicol's prism, which with the plate forms a Savart's analyser.
Soda light, first sifted by passage through a plate of potassium bichromate, traverses in succession a lens, a Nicol's prism, and a glass plate half covered with a half-wave plate of quartz, that is cut parallel to the optic axis and has its principal section inclined at a small angle to that of the prism.
The telescope must be focussed on the edge of the quartz plate, and in order that all points of the field may be illuminated by the same part of the source, the flame must be so placed that its image is thrown by the lens on the diaphragm of the object glass of the telescope.
It is clear that the light proceeds from a region surrounding the sun, and lenticular in form, the axis of the lens being nearly perpendicular to the ecliptic, while the circumference extends at least to the orbit of the earth.
Since the tenuous edge of the lens extends beyond the earth's orbit it follows that there must be some zodiacal light, whether it can be seen or not, passing entirely across the sky, along or near the ecliptic. Observations of this zodiacal band are therefore of great interest.
The most plausible view is that we have to do with sunlight reflected from meteoric particles moving round the sun within the region of the lens.
A simple microscope consists of a single positive lens, or of a lens combination acting as a single lens, placed between the eye and the object so that it presents a virtual and enlarged image.
The compound microscope generally consists of two positive lens systems, so arranged that the system nearer the object (termed the objective) projects a real enlarged image, which occupies the same place relatively to the second system (the eyepiece or ocular) as does the real object in the simple microscope.
A convex lens of rockcrystal was found by Layard among the ruins of the palace of Nimrud; Seneca describes hollow spheres of glass filled with water as being commonly used as magnifiers.
Descartes (Dioptrique, 1637) describes microscopes wherein a concave mirror, with its concavity towards the object, is used, in conjunction with a lens, for illuminating the object, which is mounted on a point fixing it at the focus of the mirror.
One leg of a compass carried the object, and the other the lens, the distance between the two being regulated by a screw.
This is effected by the power of accommodation of the eye, which can so alter the focal length of its crystalline lens that images of objects at different distances can be produced rapidly and distinctly one after another upon the retina.
Since H' P = F 0, = y, from the focal length of the simple microscope, the visual angle w' is given by tan w'/y=I/f'=V, (I) in which f', = H' F', is the image-side focal length (see Lens).
Since the lens is bounded by air, the imageand object-side focal lengths f' and f are equal.
The value Iif' or V in (I), is termed the power of the lens.
A X Jo magnification is, however, by no means guaranteed to a myopic eye of - io D by a lens of i in.
The apparent size of the object seen through the lens is then tan w' = y/f.
If the instrument has a sensible lens diameter, and is arranged so that the centre of rotation of the eye can coincide with the intersection of the principal rays, the lens can then form with the eye a centred system.
The selection of the rays emerging from the lens and actually employed in forming the image is undertaken by the pupil of the eye which, in this case, is consequently the exit pupil of the instrument.
In some instruments observation of the whole available field is only possible when the head and eye are moved at the same time, the lens retaining its position.
The distance of the eye from the lens is here immaterial.
The central projection, of which the centre is the middle point of the entrance pupil on the plane focused for, will show in weaker systems, or those very much stopped down, a certain finite depth of definition; that is to say, the totality of points, which lie out of the plane focused for, and which are projected with circles of confusion so small that they appear to the eye as sharp points, will include the sharp object relief, and determine the depth of definition of the lens.
In a lens with two bounding surfaces in air there is a loss of about 9%; and in a lens system consisting of two separated lenses, i.e.
If the ordinary convex lens be employed as magnifying glass, great aberrations occur even in medium magnifications.
The spherical aberration of a diamond lens can be brought down to one-ninth of a glass lens of equal focus.
With this mineral also spherical and chromatic aberration are a fraction of that of a glass lens, but double refraction, which involves a doubling of the image, is fatal to its use.
Coddington employed the same construction, and for this reason this device is frequently called the Coddington lens; although he brought the Wollaston-Brewster lens into general notice, he was neither the inventor nor claimed to be.
The first compound miscroscope (discovered probably by the Middelburg lens-grinders, Johann and Zacharias Janssen about 1590) was a combination of a strong biconvex with a still stronger biconcave lens; it had thus, as well as the first telescope, a negative eyepiece.
A series of objectives with short focal lengths are available, which permit the placing of a liquid between the cover-slip and the front lens of the objective; such lenses are known as " immersion systems "; objectives bounded on both sides by air are called " dry systems."
The immersion liquids in common use are water, glycerine, cedar-wood oil, monobromnaphthalene, &c. Immersion systems in which the embedding liquid, coverslip, immersion-liquid and front lens have equal refractive indices are called " homogeneous immersion systems."
The rays emitted from an axial object-point are not combined into one image-point by an ordinary biconvex lens of fixed aperture, but the central rays come to a more distant focus than the outer rays.
The lens nearer the eye, which has about the same focal length as the collective lens, is distant from it by about its focal length.
In this type the eye-lens is about twice as powerful as the collective lens, and makes the rays parallel.
The Ramsden eyepiece is the most convenient for this because this plane lies in front of the collective lens, and the objective image has not yet been influenced by the eyepiece.
It =; L 1 = front lens is simpler to place an illuminating O of microscope; lens in front of the source of light so PP =diaphragm.
By a correct choice of the focal length of the illuminating lens in relation to the focal length of the mirror, it is possible to choose the size of the image of the source of light so that the whole object-field is uniformly lighted.
It is best if the image of the light is not larger than the object examined, and to effect this, an illuminating lens with an iris diaphragm is often placed between the source of light and the illuminator.
One way of receiving a stereoscopic impression through a microscope is by fixing an apparatus as directly as possible above the last lens of the microscopic objective, which divides the rays passing out and directs half into each eyepiece.
Such a combination of prisms was used by Wenham, who placed it directly behind the last objective lens.
A fixed mark which serves as an index is placed on the lower side of the collective lens and is seen clearly at the same time as the graduation of the movable slide.
In immersion systems the immersion liquid is placed between the front lens and apertometer.
The objective to be examined is placed on the stage, and in the manner just shown, the distance of the focal plane from the edge of the fittings or to the surface plane of the front lens is determined.
Let the size of the object be y, the size of the image y' the distance of the object from the focus x, then y/y'=x/f i from which f l can be calculated (see Lens).
Like so many coloured Protista, they frequently possess a pigmented " eye-spot " in which may be sunk a spheroidal refractive body (" lens ").
Ginger, coiffed and styled by the best, was ready for a fashion photographer's lens while continually rolling her eyes with disdain toward her sister-in-law.
They are good value for money but are not optically brilliant, a small aperture essential to eliminate the aberrations of the lens.
A lens system comprising two elements, used to reduce chromatic aberration.
The theoretical resolution is never obtained due to lens aberrations which are difficult to fully compensate for in electron optical systems.
If this cannot be achieved, examine the eye again in case there is another cause for decreased acuity such as early lens opacity.
Nodular anhydrite (Arab Formation)Gypsum(dark lenticular shapes) in brown/grey lime mudstone (lens 2.5cm sq) What environment do these structures/textures occur in?
You can use the guide number to work out the lens aperture for the correct exposure at any distance.
Corneal astigmatism is when the cornea is a distorted shape and lenticular astigmatism occurs when the lens is distorted.
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Special complex diagnostic contact lens A lens used by the optician to assess performance of the design on the eye.
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Light is focused by the cornea and lens at the retina.
These proteins fill the cytoplasm of the highly organized eye lens fiber cells.
With a hand lens, the openings where the hair follicles once penetrated the dermis are easily visible.
The lens may just be tilted slightly as opposed to completely dislocated.
Photoshop Elements also allows consumers to easily correct camera lens distortion.
You've got a dud in your hands if the line distorts or wavers when the lens is rotated slightly.
The unit contains a reducing lens which restore the field of view to cover approximately the same area as standard x10 widefield eyepieces.
From this creative ferment " Leipzig Lens 2005 " brings together an exciting selection, focussed on key themes of current photographic discourse.
Police grabbed his camera leaving greasy fingerprints across the lens.
Very often the lens can capture a'moment ' too fleeting to be registered by the naked eye.
A convex lens has a focal length of 150 mm.
The research will utilize complexity theory as a lens to focus on governance frameworks.
You will then need to move the Volk lens slightly in the same direction to view the fundus again.
The light exiting the echelle grating then enters a three lens objective where it is focussed onto a detector array.
The original 4th order lens has been retained having been suitably modified to accommodate 35 watt metal halide lamps in a 3 position changer.
An orange filter on my lens increased the contrast and darkened the horizon beyond them.
Hard Candy however, has a new lens for the mass hysteria.
Fiber optic illuminator with focusing lens, brackets and trolley.
The effect of newer, bifocal, intraocular lens implants is uncertain.
The extreme perspective was gained through using my 24mm lens however I feel it has left Caroline too indistinct beneath the tree.
A sturdy carrying case with soft inners to protect each lens is part of a highly competitive deal at this price.
Canongate Kirkyard 1152 x 864 263K Photographed from far away through a long lens, an almost isometric view reminiscent of Escher.
Synthesis of a flat optical lens was investigated by using short pulsed laser induced surface graphitisation of CVD diamond in air.
The optical lens of the video camera focuses the image on the chip mounted behind the lens.
The intraocular lens will be unfolded once it is in your eye.
The lens part of the DMC-FX01 comprises of seven elements in six groups, incorporating four aspherical lenses to generate high optical performance.
The gentleman at the bus stop probably didn't realize my wide-angle lens would capture him.
The images were taken using a small magnifying lens in front of the camera lens held in place with putty.
A good lens care kit will always include soft lint free cloth, dust free tissues, cleaning fluid and a blower brush.
These normally maintain or even increase the magnification of the cameras own close up lens.
Having sufficient light is always an issue with viewing through any lens and so the illuminated headband magnifier is particularly useful.
Moving the eye closer to the lens of a hand-held or stand magnifier also increases the field of view.
Hold the film up against the window to see the tooth marks, use a hand lens magnifier to see in more detail.
Built-in magnifying lens and luminous markings for night navigation are other important features for the most demanding users.
Large feathers are easy to study under a hand lens or low power stereo microscope.
Although Lens was the first British miniaturist to work on ivory, he occasionally painted on vellum.
I have to admit to getting quite misty-eyed when I got my copy of the book God bless Karl and his lens.
The display, measuring 7.5 mm across, is to be used in viewfinders, with appropriate lens magnification.
In order to image mice a specially made contact lens is necessary to correct for severe myopia  .
Introduction of a new triple-layered DO element not only makes the lens more nimble, it delivers unrivaled imaging performance.
The degree of visual impairment induced by lens opacity differs markedly depending on the location of the opacity.
Additionally, there is a possibility that the capsule, which holds the lens, could also become opaque.
Most people visiting a high street optician are asked to indicate verbally which lens gives the sharpest image.
The camera optics were surprisingly good for what looked like a tiny pinhole lens.
The piece has been described as the critical equivalent of a long lens paparazzo shot.
But in Kinch's work, wider questions of oppression and ideology are in fact refracted through the lens of cultural particularity.
Sir Kenneth's solution was to use a small periscope which could be lowered behind the lens for focussing.
The CAA does not proscribe any type of visual correction except a single vision full lens near correction.
The powder puff was only needed once, to minimize the lens flare from Steve Castle's head.
The camera has a unique swivel lens design that gives users the flexibility to capture images from nearly any angle - including self-portraits.
When the lens is more curved, the top image appears sharper.
Because these cameras have a built-in focal-plane shutter, there is no need for a shutter in the lens.
The H System's central lens shutter allows flash sync at all shutter speeds, enabling use of flash in all lighting conditions.
They take the cataract out through a tiny slit at the edge of the sac that contains the clouded lens.
We are inviting entries from young and old, from happy snappers to experts behind the lens.
It incorporates aspherical lens elements in the front, as well as rear lens groups, to correct spherical aberration.
Its design employs three (3) aspherical lens elements to minimize spherical aberration, astigmatism and sagittal comma flare.
It does perhaps appear somewhat spotty to the naked eye but under a lens is clearly seen to be very hairy or scaled.
An amber lens distributes the high intensity strobe light in a pattern which calls immediate attention to alarms.
The optics on this unit are quite superlative, and one nice feature is the spring loaded flip up lens caps.
If cataract surgery is needed a special type of lens implant can be used instead of the ordinary implant to give better vision.
The lens loop, mounted on a 5 ml syringe, is now inserted through the incision into the eye.
Smaller tools will include a hand lens, hardness tester, color char and magnet.
Good holding torque stops the focusing lens group with precision without overshoot.
The PPI image from a high intensity cathode ray tube was projected on to the film through a focusing lens.
Photographers can fluidly move the sharp area around the photo by bending the flexible lens tubing.
The Optic System is a 300mm Acrylic lens with a 250 watt tungsten lamp controlled by an electronic flasher.
They should use a clear visor over the mask lens to prevent scratches.
Developed exclusively for the GR DIGITAL, the wide conversion lens enables ultra wide-angle 21mm photography while preserving its superior optical characteristics.
The wide converter optional lens features an ultra wide-angle 21 mm (when converted to 35 mm format camera ).
A flower shaped dedicated lens hood is included, which ensures optimum shading at both super wide-angle 19mm and standard 35mm wide-angle.
The 35mm lens is a good normal wide-angle having the advantage of all angle of field (about 650) shared by most flashguns.
Any dried on oil can be removed using xylene, but be careful as this could dissolve the cement securing the lens!
In a darkened room a beam of sunlight (or electric light) is concentrated by a large lens of 2 or 3 ft.
The divisions of both drums are conveniently read, simultaneously, by the lens e; at night the lamp which illuminates the webs and the position-circle also illuminates the drum-heads (see on illumination p. 385).
The focal length of the objective and the distance between the optical centre of the lens and the webs are so arranged that images of the divisions are formed in the plane of the webs, and the pitch of the screw is such that one division of the scale corresponds with some whole number of revolutions of the screw.
The response to the action of light in diatropic leaves is, according to Haberlandt, due to the presence of epidermal cells which are shaped like a lens, or with lens-shaped thickenings of the cuticle, through which convergence of the light rays takes place and causes a differential illumination of the lining layer of protoplasm on the basal walls of the epidermal cells, by which the stimulus resulting in the orientation of the leaf is brought about.
He was the inventor of the stage-micrometer, and of a form of heliometer; and in 1816 he succeeded in constructing for the microscope achromatic glasses of long focus, consisting of a single lens, the constituent glasses of which were in juxtaposition, but not cemented together.
Bubbles and enclosures of opaque matter, although more readily observed, do not constitute such serious defects; their presence in a lens, to a moderate extent, does not interfere with its performance (see above).
Hardness and Chemical Stability.-These properties contribute to the durability of lenses, and are specially desirable in the outer members of lens combinations which are likely to be subjected to frequent handling or are exposed to the weather.
Oughtred's English edition (1633) of the Recreations mathematiques (1627) of Jean Leurechon ("Henry van Etten") there is a quaint description, with figures, of the simple dark chamber with aperture, and also of a sort of tent with a lens in it and the projection on an inner wall of the face of a man standing outside.
From Hooke's Posthumous Works (1705), p. 127, we find that in one of the Cutlerian lectures on Light delivered in 1680, he illustrated the phenomena of vision by a darkened room, or perspective box, of a peculiar pattern, the back part, with a concave white screen at the end of it, being cylindrical and capable of being moved in and out, while the fore part was conical, a double convex lens being fixed in a hole in front.
Airy, the astronomer, about 1827, corrected his own astigmatism by means of a cylindrical lens.
Trans., 1 753, p. 156) was constructed by cutting from a complete lens abcd the equal portions aghc and acfe (fig.
Struve (Description de l'Observatoire ' Central de Pulkowa, pp. 196, 197) adds a few remarks to Steinheil's description, in which he states that the images have not all desirable precision - a fault perhaps inevitable in all micrometers with divided lenses, and which is probably in this case aggravated by the fact that the rays falling upon the divided lens have considerable convergence.
Reference should be made to the articles Reflexion, Refraction, and Caustic for the general characters of reflected and refracted rays (the article Lens considers in detail the properties of this instrument, and should also be consulted); in this article will be discussed the nature, varieties and modes of aberrations mainly from the practical point of view, i.e.
Gauss (Dioptrische Untersuchungen, GÃƒ¶ttingen, 1841), named the focal lengths and focal planes, permits the determination of the image of any object for any system (see Lens).
In optical systems composed of lenses, the position, magnitude and errors of the image depend upon the refractive indices of the glass employed (see Lens, and above, " Monochromatic Aberration ").
By compounding two lenses or lens systems separated by a definite interval, a system is obtained having a focal length considerably less than the focal lengths of the separate systems. If f and f' be the focal lengths of the combination, and f2, f2 the focal lengths of the two components, and A the distance between the inner foci of the components, then f = - f,f2/4, f' =fi f27 0 (see Lens).
If however the object-point does not lie in the medium with the index n, but before it, and the medium is, for example, like a front lens, still limited by a plane surface, just in front of which is the object-point, then in traversing the plane surface spherical aberrations of the under-corrected type again arise, and must be removed.
The second aberration which must be removed from microscope objectives are the chromatic. To diminish these a collective lens of crown-glass is combined with a dispersing lens of flint; in such a system the red and the blue rays intersect at a point (see Aberration).
What is the diameter of the glass lens of the largest refracting telescope in the United Kingdom?
He goes on to suggest that ' American concerns about global social change are refracted through the lens of infectious disease '.
With a water immersion lens however, refraction of the rays occurs on the glass - water boundaries.
A few tissues (e.g. red blood cells, eye lens) have no mitochondria, and cannot respire aerobically.
The H System 's central lens shutter allows flash sync at all shutter speeds, enabling use of flash in all lighting conditions.
We 've been up at the farm dredging the slurry pit to look for a contact lens.
A snapshot of life looked at through a different lens.
The extra converging power of a spectacle lens permits the eye to focus the image on the retina.
Spotter telescopes of between 60mm and 100mm aperture may be used to photograph the Moon simply by holding the camera lens to the eyepiece.
Photo features include an auto focus lens and a strobe flash, along with high-quality video recording.
At the end of the shot, you can see the back side of the sunglass lens.
During the brief spring, hosts of tiny wild flowers cover the tundra area; a macro lens is needed to photograph them.
The wide converter optional lens features an ultra wide-angle 21 mm (when converted to 35 mm format camera).
Urodele amphibians such as the newt can regenerate their limbs, jaws, lens, retina and large sections of the heart.
The improvement in the visual acuity of some patients was due to cataract extraction with lens implantation performed in these cases.
A shot of a broad field of action taken with a wide-angle lens.
Any dried on oil can be removed using xylene, but be careful as this could dissolve the cement securing the lens !
The z co-ordinate is the height of the camera lens above sea level.
If you are a contact lens wearer, you should proceed with extreme caution when putting on eyeshadow and eyeliner.
Eyeshadow in contact lenses can cause extreme irritation-if eyeshadow should get in one of your lenses, remove and clean the lens immediately.
With daily disposables you also don't have to worry about cleaning routines, losing lens cases, and cleaning solutions.
You just discard the lens at the end of the night and you're done.
If you were to try a lens with a base curve of 8.6, it might not fit properly and could impair your vision.
You should also be wary of online merchants who sell contact lenses without telling you the brand or manufacturer, the lens parameters, and material they're made from.
Lens coating- lens coating is a wise choice if you will be outdoors in moist conditions.
Semi-professional. They kind of cameras are often called SLRs, which means Single Lens Reflex.
Light that gets shifted through a lens is called a refractor.
If a light is bounced off of a mirror, that lens is a reflector.
Some telescopes us both lens types and they are called catadioptirics.
Being outside, the lens can attract dust and dirt, so using special cloths and cleaning liquid will help you keep the lens free of dirt and scratches.
The most common illustration of how a polarized lens works to reduce glare is to think of the lens as a Venetian blind.
A polarizing lens works when it is positioned at a 90-degree angle to the source of the glare.
For polycarbonate lenses, the polarizing film is applied to the front of the lens and covered with a scratch-resistant coating.
Select your polarized lenses carefully, as lens color does have an impact on what you see.
Blue is a popular lens color among tennis players and golfers.
Most opticians recommend an anti-reflective coating on the inside of the polarized lens.
These stresses are revealed when the light filters through the polarized lens.
You can find rectangular styles with polarized and non-polarized lens.
Often times you purchase these cameras without a lens, allowing you to select the lens that you think most appropriate for your own purposes.
It is even safe with contact lens wearers.
Almay continues to forge ahead by providing safety testing for allergies and create a line for the needs of contact lens wearers.
Smudge-proof, hypoallergenic, safe for contact lens users and easily removed with Maybelline's Moisturizing Mascara Remover, Great Lash is a drugstore beauty gem.
I was a little hesitant to order this eye shadow because it is a liquid and I am a contact lens wearer.
In addition, the mascara is advertised as smudge- and smear-proof, hypoallergenic and suitable for contact lens wearers - all great traits that spell perfection as far as I'm concerned.
Great for even the most sensitive skin and for contact lens wearers, this fresh liquid cleanser is activated when the bottle is shaken.
The formula is hypoallergenic, ophthalmologist-tested, fragrance-free and safe for sensitive skin and contact lens wearers.
To best achieve this kind of "frozen in time" effect, you may need to invest in a quality DSLR with an appropriate lens.
If the camera is a pro or semi-pro camera with exchangeable lenses, reviewers must ask themselves about the lens mount.
Can a user quickly mount a new lens to the SLR?
This is especially helpful if your camera does not feature a wide-angle lens.
Unfortunately, this camera had a fixed lens and produced poor resolution photos.
It had a fixed photo lens and could store up to 32 photos.