The first-order design of an achromat involves choosing the overall power   1   f d b l t     {\displaystyle \ {\frac {1}{\ f_{\mathsf {dblt}}\ }}\ } of the doublet and the two glasses to use. The choice of glass gives the mean refractive index, often written as n d {\displaystyle n_{d}} (for the refractive index at the Fraunhofer "d" spectral line wavelength), and the Abbe number V {\displaystyle V} (for the reciprocal of the glass dispersion). To make the linear dispersion of the system zero, the system must satisfy the equations

Refractiveindex of air

Refractiveindex of oil

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Since   f 1 = − f 2     V 2   V 1   , {\displaystyle \ f_{1}=-f_{2}\ {\frac {\ V_{2}\ }{V_{1}}}\ ,} and the Abbe numbers are positive-valued, the power of the second element in the doublet is negative when the first element is positive, and vice-versa.

Theoretical considerations of the feasibility of correcting chromatic aberration were debated in the 18th century following Newton's statement that such a correction was impossible (see History of the telescope). Credit for the invention of the first achromatic doublet is often given to an English barrister and amateur optician named Chester Moore Hall.[1][2] Hall wished to keep his work on the achromatic lenses a secret and contracted the manufacture of the crown and flint lenses to two different opticians, Edward Scarlett and James Mann.[3][4][5] They in turn sub-contracted the work to the same person, George Bass. He realized the two components were for the same client and, after fitting the two parts together, noted the achromatic properties. Hall used the achromatic lens to build the first achromatic telescope, but his invention did not become widely known at the time.[6]

Refractiveindex of lens

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The Steinheil doublet, devised by Carl August von Steinheil, is a flint-first doublet. In contrast to the Fraunhofer doublet, it has a negative lens first followed by a positive lens. It needs stronger curvature than the Fraunhofer doublet.[9]

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Several different types of achromat have been devised. They differ in the shape of the included lens elements as well as in the optical properties of their glass (most notably in their optical dispersion or Abbe number).

In the following, R denotes the radius of the spheres that define the optically relevant refracting lens surfaces. By convention, R1 denotes the first lens surface counted from the object. A doublet lens has four surfaces with radii R1 through R2 . Surfaces with positive radii curve away from the object (R1 positive is a convex first surface); negative radii curve toward the object (R1 negative is a concave first surface).

Crownglass refractiveindex

In the late 1750s, Bass mentioned Hall's lenses to John Dollond, who understood their potential and was able to reproduce their design.[2] Dollond applied for and was granted a patent on the technology in 1758, which led to bitter fights with other opticians over the right to make and sell achromatic doublets.

The default set of standards consists of a number of glass materials and high purity silicone oils. The glass standard reference materials cover a refractive index range of 1.4800 all the way to 1.5400. This range is also covered by the oils. Additionally, the oils have a thermal coefficient and a delta of that coefficient that meets the ASTM criteria for these types of tests. As part of the test methodology defined by ASTM 1967, the oil and glass standards are used to calibrate the glass refractive index measurement system prior to casework analysis. As such, this set represents a new, well characterized source for glass refractive index instrument calibration.

Refractiveindex of diamond

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Lens designs more complex than achromatic can improve the precision of color images by bringing more wavelengths into exact focus, but require more expensive types of glass, and more careful shaping and spacing of the combination of simple lenses:

Uses an equiconvex crown glass lens (i.e. R1 > 0 with −R1 = R2 ) and a complementary-curved second flint glass lens (with R3 = R2 ). The back of the flint glass lens is flat ( R4 = ∞ ). A Littrow doublet can produce a ghost image between R2 and R3 because the lens surfaces of the two lenses have the same radii.

San Dimas, CA (September 11, 2017) – CRAIC Technologies, a leading innovator of UV-visible-NIR microanalysis solutions, is proud to announce the introduction of its Glass Refractive Standards set. This set is used to calibrate instruments, such as CRAIC Technologies rIQ™ , that are designed to measure the refractive index of microscopic fragments of glass and glass-like materials. The Refractive Index Glass Standards set consists of both calibrated glass samples and immersion liquids calibrated for refractive index versus temperature. The glass materials consist of optical glass in sizes suitable for crushing and use with rIQ™ and other automated glass refractive index measurement systems. The oils are calibrated and also designed for use with automated glass refractive index measurement systems. These standard reference materials are designed to be in compliance with the standard test methodology defined by ASTM 1967.

An achromatic lens or achromat is a lens that is designed to limit the effects of chromatic and spherical aberration. Achromatic lenses are corrected to bring two wavelengths (typically red and blue) into focus on the same plane. Wavelengths in between these two then have better focus error than could be obtained with a simple lens.

'Polarize' means a single group of people forming into two separate groups, either on its own or by way of an action initiated for the purpose.

About CRAIC Technologies: CRAIC Technologies, Inc. is a global technology leader focused on innovations for microscopy and microspectroscopy in the ultraviolet, visible, and near-infrared regions.  CRAIC Technologies creates cutting-edge solutions, with the very best in customer support, by listening to our customers and implementing solutions that integrate operational excellence and technology expertise.  CRAIC Technologies provides answers for customers in forensic sciences, biotechnology, semiconductor, geology, nanotechnology and materials science markets who demand quality, accuracy, precision, speed, and the best in customer support.

where the lens power is   1   f     {\displaystyle \ {\frac {1}{\ f\ }}\ } for a lens with focal length f {\displaystyle f} . Solving these two equations for   f 1   {\displaystyle \ f_{1}\ } and   f 2   {\displaystyle \ f_{2}\ } gives

In theory, the process can continue indefinitely: Compound lenses used in cameras typically have six or more simple lenses (e.g. double-Gauss lens); several of those lenses can be made with different types of glass, with slightly altered curvatures, in order to bring more colors into focus. The constraint is extra manufacturing cost, and diminishing returns of improved image for the effort.

The first lens has positive refractive power, the second negative. R1 > 0 is set greater than −R2 , and R3 is set close to, but not quite equal to, −R2 . R4 is usually greater than −R3 . In a Fraunhofer doublet, the dissimilar curvatures of −R2 and R3 are mounted close, but not quite in contact.[7] This design yields more degrees of freedom (one more free radius, length of the air space) to correct for optical aberrations.

In the most common type (shown), the positive power of the crown lens element is not quite equalled by the negative power of the flint lens element. Together they form a weak positive lens that will bring two different wavelengths of light to a common focus. Negative doublets, in which the negative-power element predominates, are also made.

Optical aberrations other than just color are present in all lenses. For example, coma remains after spherical and chromatic aberrations are corrected. In order to correct other aberrations, the front and back curvatures of each of the two lenses remain free parameters, since the color correction design only prescribes the net focal length of each lens,   f 1   {\displaystyle \ f_{1}\ } and separately   f 2   . {\displaystyle \ f_{2}~.} This leaves a continuum of different combinations of front and back lens curvatures for design tweaks (   R 1   {\displaystyle \ R_{1}\ } and   R 2   {\displaystyle \ R_{2}\ } for lens 1; and   R 3   {\displaystyle \ R_{3}\ } and   R 4   {\displaystyle \ R_{4}\ } for lens 2) that will all produce the same   f 1   {\displaystyle \ f_{1}\ } and   f 2   {\displaystyle \ f_{2}\ } required by the achromat design. Other adjustable lens parameters include the thickness of each lens and the space between the two, all constrained only by the two required focal lengths. Normally, the free parameters are adjusted to minimize non-color-related optical aberrations.

Glass refractiveindex

CRAIC Technologies announces the availability of glass and oil standard reference materials set to calibrate glass refractive index measurement instruments

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Glass refractiveformula

Early Clark lenses follow the Fraunhofer design. After the late 1860s, they changed to the Littrow design, approximately equiconvex crown, R1 = R2 , and a flint with R3 ≃ R2 and R4 ≫ R3 . By about 1880, Clark lenses had R3 set slightly shorter than R2 to create a focus mismatch between R2 and R3, thereby avoiding ghosting caused by reflections within the airspace.[8]

“The current supplies of glass reference materials are nearly exhausted. CRAIC Technologies, with the introduction of the rIQ™ automated refractive index measurement system for glass, needed to develop a new source of reference materials for our customers” says Dr. Paul Martin, president of CRAIC Technologies.  “Our engineers have created this set of standard reference materials. This set is designed to aid in the calibration of instruments like rIQ™ and as such have been well characterized in terms of their refractive index and in accordance to the test methodology ASTM 1967.”

One mil is equal to one thousandth of an inch. In metric expression one mil equals to 0.0254 mm. MPY is used to calculate the lifetime of metallic surfaces.

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For more information on the Refractive Index Glass Standards set and the rIQ™ glass refractive index measurement system, visit http://www.microspectra.com.

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Refractiveindex of water

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The use of oil between the crown and flint eliminates the effect of ghosting, particularly where R2 ≈ R3 . It can also increase light transmission slightly and reduce the impact of errors in R2 and R3 .

The most common type of achromat is the achromatic doublet, which is composed of two individual lenses made from glasses with different amounts of dispersion. Typically, one element is a negative (concave) element made out of flint glass such as F2, which has relatively high dispersion, and the other is a positive (convex) element made of crown glass such as BK7, which has lower dispersion. The lens elements are mounted next to each other, often cemented together, and shaped so that the chromatic aberration of one is counterbalanced by that of the other.

Dialyte lenses have a wide air space between the two elements. They were originally devised in the 19th century to allow much smaller flint glass elements down stream since flint glass was hard to produce and expensive.[10] They are also lenses where the elements can not be cemented because R2 and R3 have different absolute values.[11]

The descriptions of the achromat lens designs mention advantages of designs that do not produce "ghost" images. Historically, this was indeed a driving concern for lens makers up to the 19th century and a primary criterion for early optical designs. However, in the mid 20th century, the development of advanced optical coatings for the most part has eliminated the issue of ghost images, and modern optical designs are preferred for other merits.