Achromatic Sentence Examples
This was applied to an excellent achromatic telescope of 34 in.
It will be seen, then, that the visual and photographic foci are now merged in one, and the image is practically as achromatic as that yielded by a reflector.
If not, the substitution of an achromatic lens will be of no advantage.
The lens of the human eye is not achromatic.
The reflecting telescope became the only available tool of the astronomer when great light grasp was requisite, as the difficulty of procuring disks of glass (especially of flint glass) of suitable purity and homogeneity limited the dimensions of the achromatic telescope.Advertisement
There are also other eye-pieces having the field-lens double or achromatic as well as the eye-lens.
Especially powerful achromatic condensers are really only magnified microscope objectives, with the difference that they are not corrected for the thickness of the cover slip, but for the thickness of the glass on which the object is placed.
His skill as a working lapidary was very great; and he prepared a number of lenses of garnet and other precious stones, which he preferred to the achromatic microscopes of the time.
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.
It is clearly established that Hall was the first inventor of the achromatic telescope; but Dollond did not borrow the invention from Hall without acknowledgment in the manner suggested by Lalande.Advertisement
The substitution of a positive or negative eye-piece for the simple convex or concave eye-lens, and of an achromatic object-glass for the simple object-lens, transforms these, early forms into the modern achromatic telescope.
In spite of the improvements in the manufacture of optical glass practically the same crown and flint glasses as used by John Dollond in 1758 for achromatic objectives are still used for all the largest of the modern refracting telescopes.
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 is such a practical drawback that the separation is generally 4ths or $ths of the theoretical, and then the primary image viewed by the eye piece may be rather outside the field-lens, which is a great practical advantage, especially when a reticule has to be mounted in the primary focal plane, although the edge of the field is not quite achromatic under these conditions.
In cases where it is important to get the maximum quantity of light into the eye, the field-lens is discarded and an achromatic eye-lens alone employed.Advertisement
Those silver-on-glass specula are now the rivals of the achromatic telescope, and it is not probable that many telescopes with metal specula will be made in the future.
The absence of this error is termed achromatism, and an optical system so corrected is termed achromatic.
James Gregory and Leonhard Euler arrived at the correct view from a false conception of the achromatism of the eye; this was determined by Chester More Hall in 1728, Klingenstierna in 1754 and by Dollond in 1757, who constructed the celebrated achromatic telescopes.
Among them were an elegant solution of the problem to determine the orbit of a comet from three observations, and memoirs on the micrometer and achromatic telescopes.
To an achromatic collective lens, which is turned towards the object, a dispersive lens is combined (this type to a certain extent belongs to the compound microscope).Advertisement
Good apochromats often have as many as twelve lenses, whilst systems of simpler construction are only achromatic, and are therefore called " achromats."
Selligue had no particular comprehension of the problem, for his achromatic single systems were simply telescope objectives corrected for an infinitely distant point, and were placed so that the same surface was turned towards the object in the microscope objective as in the telescope objective; although contrary to the telescope, the distance of the object in the microscope objective is small in proportion to the distance of the image.
This system will always be aplanatic. These objectives permitted a much larger aperture than a simple achromatic system.
The weak compensation oculars resemble a Huygenian eyepiece with achromatic eye-lens, whilst the more powerful ones are of a different construction.
As powerful achromatic objectives show differences of chromatic magnification in the same way as apochromats, compensation eyepieces can be used in combination with these objectives.Advertisement
But it was difficult to make small high power achromatic lenses.
If you are using an achromatic refractor, the focus errors will be larger due to chromatic aberration of the telescope.
There is a little bit of color shift but the filter looks like a good addition to an achromatic refractor.
Achromatic and chromatic colors Broadly speaking, colors are divided into achromatic and chromatic colors.
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.
In spite of the improvements in themanufacture of optical glass (see Glass) practically the same crown and flint glasses as used by John Dollond in 1758 for achromatic objectives are still used for all the largest of the modern refracting telescopes.
The great reflecting telescope at Dorpat was manufactured by him, and so great was the skill he attained in the making of lenses for achromatic telescopes that, in a letter to Sir David Brewster, he expressed his willingness to furnish an achromatic glass of 18 in.
He also succeeded in constructing an almost perfectly achromatic eye-piece, still known by his name.
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.
It must be remembered, however, that when Dollond expressed preference for this third type he had not then invented the achromatic object-glass.
Given the achromatic object-glass, why should not it be divided ?
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.
Hall in 1733 constructed achromatic lenses.
In these very long telescopes This last power could not be exceeded with advantage in this form of telescope till after the invention of the achromatic objectglass.
The historical sequence of events now brings us to the discovery of the achromatic telescope.
The first person who succeeded in making achromatic refracting telescopes seems to have been Chester Moor Hall, a gentleman of Essex.
It was known that, about seven years after the patent for making achromatic object-glasses was granted to Dollond, his claim to the invention was disputed by other instrument-makers, amongst them by a Mr Champness, an instrument-maker of Cornhill, who began to infringe the patent, alleging that John Dollond was not the real inventor, and that such telescopes had been made twentyfive years before the granting of his patent by Mr Moor Hall.
John Dollond, to whom the Copley medal of the Royal Society had been the first inventor of the achromatic telescope; but it was ruled by Lord Mansfield that" it was not the person who locked his invention in his scrutoire that ought to profit for such invention, but he who brought it forth for the benefit of mankind."3 In 1747 Leonhard Euler communicated to the Berlin Academy of Sciences a memoir in which he endeavoured to prove the possibility of correcting both the chromatic and.
Adopting a hypothetical law of the dispersion of differently coloured rays of light, he proved analytically the possibility of constructing an achromatic object-glass composed of lenses of glass and water.
It appears that workmen who had been employed by Mr Moor Hall were examined, and proved that they had made achromatic object-glasses as early as 1733.
For an achromatic dispersive lens the converse must be adopted.
Nevil Mas kelyne, who succeeded him in 1764, set on foot, in 1767, the publication of the Nautical Almanac, and about the same time had an achromatic telescope fitted to the Greenwich M aske mural quadrant.
A similar argument may be applied to find at what point an achromatic lens becomes sensibly superior to a single one.
When mitosis is about to take place, they separate from one another and pass to the poles of the nucleus, forming the achromatic spindle.
In many pathological cells undergoing indirect segmentation, centrosomes appear to be absent, or at any rate do not manifest themselves at the poles of the achromatic spindle.
Some excellent instruments of the second type were subsequently made by Dollond's eldest son Peter, in which for the " convex glass within the tube " was substituted an achromatic object-glass, and outside that a divided negative achromatic combination of long focus.
To Fraunhofer, some time not long previous to 1820, is due, so far as we can ascertain, the construction of the first heliometer with an achromatic divided object-glass, i.e.