what are the material properties of the lens course hero

What are the different types of lens properties?

Lenses can be produced using a variety of materials and designed with several optical profiles to optimize use in specific applications. Critical lens properties include refractive index, Abbe number (chromatic dispersion), specific gravity, and ultraviolet absorption. Figure 1. Indices of refraction of various materials and lenses. [2]

What materials are lenses made out of?

Rudolf Kingslake, R. Barry Johnson, in Lens Design Fundamentals (Second Edition), 2010 The most common lens material is, of course, optical glass, but crystals and plastics are frequently used, while mirrors can be made of essentially anything that is capable of being polished.

What are the critical lens properties?

Critical lens properties include refractive index, Abbe number (chromatic dispersion), specific gravity, and ultraviolet absorption. Figure 1. Indices of refraction of various materials and lenses.

What is the reflectance of a lens material?

Thus a material of refractive index 1.5, has a reflectance of The transmittance of a lens material describes the amount of light (usually specified for a given waveband) that will pass through that material. Glass has historically been the material of choice for ophthalmic lenses.

What are the critical properties of lenses?

What is corrective spherocylindrical lens?

What is a trivex lens?

What is the point of optimization where chromatic aberration is minimized?

How to correct chromatic aberration?

What is the purpose of a flint lens?

What is a high index lens?

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PROPERTIES OF LENSES - University of Florida

Let us now let the right ray impinge on the lens at x=x0 and y=y0.According to Snell’s Law the ray will bend according to- n 1 sin( 1) n 2 sin( 2),where the ns are the indexes of refraction of the outside air and the assumed crown glass lens and the

Eyeglass Lens Materials - Master Eye Associates

Polycarbonate lenses have a higher index of refraction (1.586) than CR-39 plastic (1.498) and are therefore thinner in an equal lens prescription. With a higher index (of refraction), light is bent more efficiently, therefore it requires less material to achieve the eyeglass prescription making the lenses much lighter.

Optical Materials Important properties - University of Arizona

J. H. Burge University of Arizona 1 Optical Materials . Important properties: • Optical o Wavelength range o Refractive index o Dispersion o dn/dT o Optical quality transmission, bubbles, homogeneity, birefringence, .. • Mechanical o CTE o Young’s modulus o Density o Thermal conductivity o Specific heat o Hardness o Melting point o Fracture toughness

Your Guide to Eyeglass Lens Materials - VSP

Based on your prescription, frame selection, and lifestyle needs, your VSP network doctor can recommend the best lens materials for you. Here is a quick guide on some of the materials you may hear about at your appointment.

What are the critical properties of lenses?

Critical lens properties include refractive index, Abbe number (chromatic dispersion), specific gravity, and ultraviolet absorption.

What is corrective spherocylindrical lens?

Corrective spherocylindrical lenses are commonly used to treat refractive errors such as myopia, hyperopia, presbyopia, and astigmatism. Both lenses and prisms are also frequently used to improve eye alignment and treat diplopia in strabismus. Eyeglasses also serve an important role in protecting the eyes from physical trauma and harmful radiation.

What is a trivex lens?

A disadvantage of Trivex lenses is its low index of refraction, thus requiring thicker lenses for higher powers. At the ±3.00 Diopter prescription range, this material allows for a comparably thin lens. Trivex is the lightest material available and meets high-velocity impact standards. A scratch-resistant coating is required for this lens.

What is the point of optimization where chromatic aberration is minimized?

This point of optimization where chromatic aberration is minimized is called the circle of least confusion. The achromatic lens is the most commonly used commercial lens, referred to as a doublet, and can drastically reduce the chromatic focal shift.

How to correct chromatic aberration?

Chromatic aberration can be corrected by combining the crown and flint glass elements to make a compound lens. This is achieved by apposing the two lenses and shaping them so that the chromatic aberration of one is neutralized by the other. The ultimate goal is to reduce the chromatic focal shift—the distance between focal points of dispersed wavelengths by a lens—between different wavelengths on the visible spectrum.

What is the purpose of a flint lens?

They are particularly useful for imaging applications as they minimize chromatic aberrations. Flint glasses are optical glasses with high chromatic aberration (Abbe number below 50) which tend to have a high refractive index (typically greater than 1.55).

What is a high index lens?

High-index materials. High-index materials are defined by a refractive index of 1.60 or higher , and can be either glass or plastic. The main utility of high-index lenses is for high-power prescriptions to create thin and cosmetically attractive lenses.

What is the most impact resistant lens material?

Polycarbonate. While its optical characteristics are less than ideal, polycarbonate, the same material used for bullet-proof glass, is the most impact resistant of lens materials. Consequently, polycarbonate is the material of choice for safety and children’s eyewear. With an index of 1.59, polycarbonate also produces thinner, ...

What is the tendency of a material to separate light in this manner?

The tendency to of a material to separate light in this manner is called chromatic aberration and is measured by its Abbe value. The Abbe value of a material is inversely proportional to the chromatic aberration induced as light passes through it.

What is high index lens?

High index lenses polymers typically refer to products with an index higher than 1.58. High index lenses require flatter curves than their lower index counterparts, resulting in thinner and lighter lenses. Furthermore, aspheric curves come standard in many high index products, particularly 1.66 and 1.70 products, and are available in 1.60. Asphericity reduces spatial distortion, reduces magnification or minification, and further helps maintain a thin and flat lens profile. High index material, however, tends to have a lower Abbe value which could potentially affect patients who are sensitive to chromatic aberration. Also higher index and flatter curves tend to result in more backside and inner-surface reflections. AR coatings are usually recommended for high index lenses to eliminate these reflections.

What is the refractive index of a lens?

The refractive index of a lens material indicates how much the material will refract or bend light as it enters the material from air, by comparing the speed of light in a given material to the speed of light in air. The higher the index number of a given material, the more the light will refract as it enters the material.

What happens when the index number of a material is higher?

The higher the index number of a given material, the more the light will refract as it enters the material. If a material has a greater ability to refract light, less of a curve is required to obtain a specific power, resulting in a thinner lens.

How does specific gravity work?

Specific gravity describes the density of a lens material by comparing its density to the density of water. The higher the specific gravity of a lens material, the higher the density, and consequently, the heavier a lens of that material will be for a given power and size.

Why are glasses tempered?

However, since glass is more brittle than most materials, lenses made of glass must be tempered or heat-treated to give them more strength and make them safer to wear. Glass is available in a number of indices of refraction. As mentioned above, the higher the index, the thinner a lens will be for a given power.

What are the chemical properties of lenses?

CHEMICAL PROPERTIES  chemical properties shows the reaction of materials to the chemical substances usually found during lens manufacture, in every day life, or to certain extreme conditions to which materials can be subjected.  These substances are usually hot or cold water, acids and organic solvents. 91. 92.

What is plastic lens?

PLASTIC LENS MATERIAL  It is a polymeric material of large molecular wt. which can be shaped by flow  Also called as organic lenses.  Most plastics are synthetic materials formed by combining various organic ingredients with inorganic materials such as carbon, hydrogen, ,nitrogen, chlorine & Sulphur. 30. 31.

When were eyeglasses invented?

 Eyeglass lenses made from polycarbonate were introduced in the early 1980s in response to demand for lightweight impact resistance lenses. 44. 47.

What are contact lens materials called?

Lens materials have three names: (1) the scientific chemical name; (2) the USAN name; and (3) the trade name. Contact lens materials are rarely called by their scientific chemical name, but rather by their USAN name in the scientific literature. The United States Adopted Names Council (USANs), which provides the generic or nonproprietary names of all drugs and therapies marketed in the United States, also names all contact lens materials. The generic name is officially called the United States Adopted Name (USAN), and serves as an important and unique designation for the active ingredient or material. It appears with the company’s trade name on labels, advertisements, and other information, and is also requested on FDA applications and in drug substance chemical descriptions. Because most journals request that authors use the generic name in clinical trial reports, it is used in publishing scientific data about investigational and established therapies/materials. The USAN is also much shorter, easier to remember, and more pronounceable than the scientific chemical name. For example, Etafilcon A is the USAN name for poly2-hydroxyethyl methacrylate-co-methacrylic acid marketed under the trade name of Acuvue by Vistakon (a division of Johnson & Johnson, Inc.).

When the temperature of a hot object in the open is being measured, due regard must be given to the correction?

When the temperature of a hot object in the open is being measured, due regard must be given to the correction required for the difference between the emissivity of the surface of the object and that of a perfect blackbody.

How does an optical thermometer affect radiation?

Like the total radiation thermometer, the optical thermometer is affected by the emissivity of the radiation source and by any absorption of radiation , which may occur between the radiation source and the instrument.

Why are infrared materials not visible?

33 With few exceptions, they are not generally usable in the visible, however, because of light scatter at the crystal boundaries.

What are mirrors made of?

The most common lens material is, of course, optical glass, but crystals and plastics are frequently used, while mirrors can be made of essentially anything that is capable of being polished.

Why is a camera lens yellow?

A trace of yellow color is often insignificant in a very small or a very thin lens and, of course, in aerial camera lenses yellow glass is quite acceptable because the lens will be used with a yellow filter anyway.

How do glasses differ from each other?

Optically, glasses differ from one another in respect to refractive index, dispersive power, and partial dispersion ratio, while physically they differ in color, density, thermal properties, chemical stability, bubble content, striae, and ease of polishing.

What is modulus in contact lens?

2. The modulus (cross-sectional stress/strain) of a contact lens is a measure of the material’s stiffness. 4 Modulus should be a concern for the contact lens practitioner because materials with a higher modulus are associated with mechanically induced complications such as giant papillary conjunctivitis and superior epithelial actuate lesions. 4 Low water content soft contact lenses usually have higher moduli, and high water content contact lenses typically have lower moduli, though there are exceptions to this trend. 4 Material modulus can also vary slightly with temperature. 4

What is contact angle?

3. A contact lens’ contact angle (angle formed between a surface and drop of liquid) is a measure of the wettability of a contact lens; smaller angles indicate that materials are more wettable while larger angles indicate that a material is less wettable. 5 Contact lens contact angles are material dependent, with no clear difference between ...

What is coefficient of friction?

5. The coefficient of friction can be defined as the “ratio of lateral to normal forces acting between two surfaces in relative motion.” 9 The coefficient of friction for soft contact lenses is highly material variable (no clear differences between traditional and silicone hydrogel contact lenses), but it may increase with increasing amounts of contact lens deposits. 9 Higher coefficients of friction are also believed to result in lower levels of contact lens comfort. 9

Do contact lenses work?

Currently marketed contact lenses have been developed to work in synergy with the eye and to allow for healthy and regular use. This has been accomplished by taking into account the many contact lens properties described above. Furthermore, the continual need to improve upon biocompatibility and ocular comfort has resulted in a myriad of contact lens prescribing options. On the surface, a multitude of very similar soft contact lenses may seem redundant and unnecessary; however, small differences in the materials properties described above may lead to a big perceived difference for our patients that will likely not be consistent across patients, and because of this there will likely always be a need for a variety of soft contact lenses materials in the market, a concept that should always be considered when dealing with those hard to fit patients.

Do hydrogel contacts dehydrate?

3, 8 Dehydration of traditional hydrogel contact lenses can reduce oxygen transmissibility, which may increase the chances of hypoxic complications, while the opposite relationship is true for silicone hydrogel contact lenses. 3 Silicone hydrogel contact lenses dehydrate less than hydrogel contact lenses, and there is currently no clear relationship between contact lens comfort and contact lens dehydration. 3

What is crown glass?

Crown glass is mineral glass, but made with a higher Melting Point

What is the ratio of weight of a substance to the weight of water with the same volume?

Specific Gravity: ratio of weight of a substance to the weight of water with the same volume (measurement of physical density).

What are the critical properties of lenses?

Critical lens properties include refractive index, Abbe number (chromatic dispersion), specific gravity, and ultraviolet absorption.

What is corrective spherocylindrical lens?

Corrective spherocylindrical lenses are commonly used to treat refractive errors such as myopia, hyperopia, presbyopia, and astigmatism. Both lenses and prisms are also frequently used to improve eye alignment and treat diplopia in strabismus. Eyeglasses also serve an important role in protecting the eyes from physical trauma and harmful radiation.

What is a trivex lens?

A disadvantage of Trivex lenses is its low index of refraction, thus requiring thicker lenses for higher powers. At the ±3.00 Diopter prescription range, this material allows for a comparably thin lens. Trivex is the lightest material available and meets high-velocity impact standards. A scratch-resistant coating is required for this lens.

What is the point of optimization where chromatic aberration is minimized?

This point of optimization where chromatic aberration is minimized is called the circle of least confusion. The achromatic lens is the most commonly used commercial lens, referred to as a doublet, and can drastically reduce the chromatic focal shift.

How to correct chromatic aberration?

Chromatic aberration can be corrected by combining the crown and flint glass elements to make a compound lens. This is achieved by apposing the two lenses and shaping them so that the chromatic aberration of one is neutralized by the other. The ultimate goal is to reduce the chromatic focal shift—the distance between focal points of dispersed wavelengths by a lens—between different wavelengths on the visible spectrum.

What is the purpose of a flint lens?

They are particularly useful for imaging applications as they minimize chromatic aberrations. Flint glasses are optical glasses with high chromatic aberration (Abbe number below 50) which tend to have a high refractive index (typically greater than 1.55).

What is a high index lens?

High-index materials. High-index materials are defined by a refractive index of 1.60 or higher , and can be either glass or plastic. The main utility of high-index lenses is for high-power prescriptions to create thin and cosmetically attractive lenses.