A metallurgical microscope is a special version of a standard light microscope for the study of materials, such as Metals, plastics, ceramics and others. Since materials are usually not transparent solid structures, metallurgical microscopes often have an upright light unit. Moreover, this type of microscope is characterized by extensive magnification, e.g. for detailed investigations of surface structures. Application areas of metallurgical microscopy are industry, material science and research.

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Applying anti-reflective coating to eyeglass lenses is a highly technical process involving vacuum deposition technology.

Also, don’t attempt to clean AR-coated lenses without wetting them first. Using a dry cloth on a dry lens can cause lens scratches. And because anti-reflective coating eliminates light reflections that can mask lens surface defects, fine scratches often are more visible on AR-coated lenses than on uncoated lenses.

Anti-reflective coating (also called “AR coating” or “anti-glare coating”) improves vision, reduces digital eye strain and makes your eyeglasses look more attractive. These benefits are due to the ability of AR coating to virtually eliminate reflections from the front and back surfaces of your eyeglass lenses.

With reflections gone, more light passes through your lenses to optimize visual acuity with fewer distractions (especially at night), and the lenses look nearly invisible — which enhances your appearance by drawing more attention to your eyes and helping you make better eye contact with others.

Standard bright-field microscopes are used for daily laboratory routine in research and diagnostics for simple, standard applications that require no special equipment. Therefore simple optical systems and lenses are applied.

When cleaning AR-coated lenses, use only products that your optician recommends. Lens cleaners with harsh chemicals may damage the anti-reflective coating.

Phase contrast microscopy is a contrast-enhancing technique to visualize structures difficult to detect with bright-field microscopy due to a lack of contrast, without the need of a staining. When penetrating a medium, light propagates with different speeds depending on the refractive index of the medium. This leads to phase differences, which are converted to differences in brightness by the microscope using phase rings. Areas of application of phase contrast microscopes are mainly the observation of living biological samples in order to resolve fine structures with high contrast.

While the lens racks are rotating in the coating chamber, a power source within the machine focuses a beam of electrons onto a small crucible that contains a series of metal oxides in separate compartments.

Some eyeglass lenses have factory-applied AR coating on both lens surfaces. Other lenses, particularly progressive lenses and other multifocal lenses (bifocals and trifocals), have the coating applied after the lenses have been customized to your eyeglass prescription by an optical lab.

Most premium AR lenses include a surface treatment that seals the anti-reflective layers and makes the lenses easier to clean. These hydrophobic surface treatments also repel water, preventing the formation of water spots on your lenses.

Anti-reflective coating also is a good idea for sunglasses. It eliminates glare from sunlight reflecting into your eyes from the back surface of tinted lenses when the sun is behind you. (Generally, AR coating is applied only to the back surface of sunglass lenses because there are no cosmetic or visual benefits to eliminating reflections from the front surface of dark-tinted lenses.)

The lenses are then loaded into special metal racks with spring-loaded openings so the lenses are held securely but with virtually all lens surfaces exposed for the coating application. The racks are then loaded into the coating chamber. The door of the chamber is sealed, and the air is pumped out of the chamber to create a vacuum.

Today’s modern anti-reflective coatings can virtually eliminate the reflection of light from eyeglass lenses, allowing 99.5% of available light to pass through the lenses and enter the eye for good vision.

An inverted microscope is an upside-down standard light microscope. This type of microscope is characterized by locating the objective underneath the stage and pointing upwards to the specimen. Inverted microscopes are mainly used for live cell analysis of cell cultures growing in culture medium. Culture dishes are not only available with standard coverslip bottoms (thickness 0.17mm) but also in various material and bottom thicknesses. Therefore, for some models special objectives are available that can correct for different bottom glass thicknesses. In addition, inverse microscopes are also used for studies of thicker specimens. Inverted microscopes are also available as dark field, polarization or fluorescence microscopes.

For example, regular plastic lenses reflect roughly 8% of light hitting the lenses, so only 92% of available light enters the eye for vision.

Some anti-reflective lenses have surface treatments that are both hydrophobic and oleophobic (also called lipophobic), which means they repel both water and oil. These combination treatments typically contain fluorinated materials that give the lenses properties that are very similar to those of nonstick cookware.

A dark field microscope produces a contrast-enhanced image by indirect illumination of the specimen, thereby also unstained specimens can be displayed with high contrast. Using this technique, direct light is bypassing the objective, only light scattered by the specimen enters the objective. As a result, the background appears dark or black, only the specimen is illuminated and even small structures can be visualized with high contrast. Dark field microscopy in biology and medicine is especially used for transparent and low contrast specimens, for example, studying blood, small animals or micro-particles in material science.

By eliminating reflections, AR coating also makes your eyeglass lenses look nearly invisible so people can see your eyes and facial expressions more clearly. Anti-reflective glasses also are more attractive, so you can look your best in all lighting conditions.

dark-field microscopy

Polarization microscopy is used for the analysis of optically anisotropic samples. The primary objective of polarization microscopy is not magnification of an object, but rather the analysis of optical properties such as refractive index or birefringence for sample analysis. The method is mainly used in mineralogy and in industry for testing plastics or mineral building materials in order to gain insights into their composition.

High index plastic lenses can reflect up to 50% more light than regular plastic lenses, so even less light is available to the eye for vision. This can be particularly troublesome in low-light conditions, such as when driving at night.

The physical principle of fluorescence is used to selectively visualize and localize defined fluorescent structures, while non-fluorescent structures remain dark in order to obtain a high image contrast. For this purpose, fluorescent dyes (fluorochromes) are used with specific excitation and emission filters installed in the optical path of the microscope. A wide range of fluorescent dyes with different colors are available, which are used in molecular biological, biomedical and clinical research. For example, in immunohistochemistry, fluorescence-in-situ-hybridization and for visualization of cells or cellular components in living/fixed specimens.

Typically, a production line includes multiple washing and rinsing baths, including ultrasonic cleaning to remove any traces of surface contaminants. This is followed by air drying and heating of the lenses in special ovens to further remove unwanted moisture and gases from the lens surface.

When applied to photochromic lenses, AR coating enhances the clarity and comfort of these premium lenses in all light conditions without reducing their sun-reactive performance.

When the coating materials are bombarded by electrons, they vaporize within the coating chamber and adhere to the surfaces of the lenses — creating a uniform, microscopically thin optical layer on the lens.

Depending on your lifestyle, your optician might suggest a specific brand of anti-reflective coating. If you spend a lot of time working at a computer, you might benefit from an AR coating that filters out blue light (example: Essilor’s Crizal Prevencia).

Anti-reflective coatings are incredibly thin. The entire multilayer AR coating stack generally is only about 0.2 to 0.3 microns thick, or about 0.02% (two one-hundredths of 1%) of the thickness of a standard eyeglass lens.

Depending on the AR coating formula, most lenses with anti-reflective coating have a very faint residual color, usually green or blue, that is characteristic of that particular brand of coating.

AR coating is especially beneficial when used on high-index lenses, which reflect more light than regular plastic lenses. Generally, the higher the index of refraction of the lens material, the more light that will be reflected from the surface of the lenses.

Bright field dark field

The first step in the AR coating process is to meticulously clean the lenses and inspect them for visible and microscopic surface defects. Even a tiny smudge, piece of lint or hairline scratch on a lens during the coating process can cause a defective AR coating.

The visual benefits of lenses with anti-reflective coating include sharper vision with less glare when driving at night and greater comfort during prolonged computer use (compared with wearing eyeglass lenses without AR coating).

Each AR coating manufacturer has its own proprietary formula, but generally all anti-reflective coatings consist of multiple microscopic layers of metallic oxides of alternating high and low index of refraction. Since each layer affects different wavelengths of light, the more layers there are, the more reflections that are neutralized. Some high-quality AR coatings have up to seven layers.