Reasons for Camera Lens Optical Coatings

Coatings change the manner in which
the lens transmits and reflects light

Camera lens optical coatings almost always use a thin Magnesium Flouride (MgFL) layer. A vacuum chamber is used to apply them. A solitary optical coating will typically be a subtle blue color as one views the surface of the lens at a slight angle. Multi-Coated lens most often have a purple or green tint to the exterior surface.

Multi-coated Sigma 50-500mm Lens with Green Coating
Multi-coated Sigma 50-500mm Lens with Green Coating

These coatings change the manner in which the lens transmits and reflects light. One particular type of coating for optics is antireflection, which diminishes superfluous reflections on surfaces, and is typically used on eye glases and photographic lenses. Another coating type is high-reflector coat which is used to create mirrors which reflect an excess of 99.99% of light reaching them. More complex types of optical coatings demonstrate high reflection over several ranges of wavelengths, plus anti-reflection over other ranges, allocating for fabricating dichroic thin-film filters.

Voigtlander 28mm lens with red coating
Voigtlander 28mm lens with red coating

Coating Types

The most simple optical coatings use thin metal layers, like aluminum, which are attached to glass substrates to create mirror surfaces, a practice called silvering. The type of metal used establishes the mirror's reflection characteristics; aluminum being the cheapest and most typical coating, and produces a reflectivity between 88%-92% for the detectable spectrum. Silver is more expensive, although it has a 95%-99% reflectivity all the way to the extreme infrared, but experiences decreasing reflectivity (<90%) for the ultraviolet and blue spectral areas. Gold is the most expensive, which provides exceptional (98%-99%) reflectivity through the entire infrared, however limited reflectivity with wavelengths less than 550 nm, producing the common gold color.

It's possible to lessen the reflectivity and intensify the transmission to the exterior surface by managing the density and thickness of metal coatings, concluding in a mirror that's half-silvered which are typically employed for "one-way mirrors".

Dielectric coating is the other chief optical coating type (i.e. using materials with unique refractive indexes to the substrate). These are created using thin sheets of materials like calcium fluoride, magnesium fluoride, and other types of metal oxides, that are affixed to the optical substrate. By carefully choosing of the precise composition, number of layers and thickness, it's possible to adapt the transmitivity and reflectivity of the coatings to create almost any desired trait.

Coefficient reflections of surfaces may be decreased to under 0.2%, creating an antireflection (AR) coat. On the other hand, this reflectivity may be increased to an excess of 99.99%, creating a high-reflection (HR) coating. The reflectivity level can also be fine-tuned to any rate in particular, for example, to create a mirror which reflects 90% and reflects 10% of the illumination arriving at it, over a particular range of wavelengths. These types of mirrors are typically used as beam-splitters, and also output couplers used in lasers. Consequently, the coating may be engineered such a fashion that the mirror will reflect only light in a thin wavelength band, thus, creating an optical filter.

The resourcefulness of dielectric coatings establishes a path to being used in many optical scientific instruments (like optical microscopes, lasers, interferometers. and refracting telescopes) along with consumer devices like photographic lenses, eye glasses, and binoculars.

Dielectric layers are applied at times in addition to metal films, as a way to supply a protective layer (like silicon dioxide on top of aluminum), or as a way of augmenting the metal film's reflectivity. Dielectric and metal combinations are also employed to create advanced coatings that are unable to be produced in any other way. One situation is the so-labeled "perfect mirror", which produces high (although not quite perfect) reflection, having unusually minimal wavelength sensitivity to angle, and polarization.

N-Nano Crystal Coat
Nano Crystal Coat consist of an antireflective coat that stemmed from the cultivation of Nikon NSR-series (Step and Repeat type) semiconductor fabricating devices. It virtually eradicates internal lens element manifestations throughout a wide variety of wavelengths, which is specifically effectual in minimizing ghost and flare atypical to an ultra-wide-angle lens. Nano Crystal Coat uses multiple layers of extra-low refractive index coatings, and includes ultra-fine crystallized fragment of nano size (a single nanometer is equal to one millionth of a single mm). A world first was scored by Nikon with pride by utilizing this technology for coating a wide variety of consumer optical lenses

NIC - Nikon Integrated Coating. In past years, light reflecting off of specific lens elements including the glass itself absorbing light caused a massive amount of problems, including ghosting, poor contrast, flare, and distorted color rendition. n the early 1970's as various camera manufactures' started applying anti-reflective microscopically thin multiple layers of material to lens elements immense progress was made

However, unlike other companies who willy niilly apply the identical number of lens coatings to every element irrespective of its nature or the glass employed, the Nikon multilayer coating procedure is incorporated into the engineering of a particular lens. Only the correct amount of coatings are put on each lens element to match the type of lens and the glass used which is done inside a vacuum chamber.

The results are remarkable increases in actual image contrast and light transmission plus a corresponding decrease in flare created by internal reflections. However more important uniform color stability from one lens to another is accomplished throughout the entire Nikon Series . Now, (NIC) is a complicated procedure, but then optical superiority demands nothing less.

SIC - Nikon Super Integrated Coating
Nikon uses an elite multilayer lens coating to augment the operation of its lens elements which also helps diminish ghosting and flare to minute levels. Nikon Super Integrated Coat also accomplishes several purposes, including reduced reflection in the broader wavelength ranges including exceptional color calculations and reproduction. NIC is particularly effective for lenses employing a large amount of elements, like the Nikon Zoom lenses. In addition, Nikon's multilayer coating procedure is customized for each individual lens design. The specific number of coatings that are added to every lens element is precisely formulated to complement the lens style and the type of glass employed and also to maintain the consistent color balance that epitomizes Nikon lenses. The effects are lenses that have loftier levels than others in the camera lens industry

Super Spectra coatings
Canonís Super Spectra lens coating is used to prevent flare and ghosting. These are more prone to occur with digital cameras due to reflection off the image sensor. The use of optimized lens coatings prevent flare and ghosting and ensure excellent color balance and contrast.

updated article Oct 10, 2011

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