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Interchangeable Lenses—The Nano Crystal Coat—Revolutionary Lens Technology that Dramatically Reduces Ghosts and Flare

1. Digital cameras with more megapixels, and interchangeable lenses

Even with the same number of pixels, digital cameras come in numerous types

Digital cameras are in wide use these days, and most professional photographers also use digital cameras now, probably because the quality of digital pictures has reached the level that these photographers require. So how do we determine the picture quality of a digital camera?

The number of pixels of the image sensor is one criterion used to judge picture quality. Digital cameras nowadays have an increasingly higher numbers of pixels, and currently some mobile phones even have camera functions with as many as 5 million pixels. Nevertheless, despite having the same 5 million pixels, there are clear differences in the quality of images taken by a camera-equipped mobile phone, a compact digital camera, and a digital SLR camera. Why does this happen? It happens because the analog information prior to digital processing is dependent on the performance of the lens through which light passes, and this has a major influence on ultimate image quality. In other words, if the performance of the lens that sends light to the sensor is not up to par, the resulting digital image, no matter how many pixels it has, will not be of high quality. A digital SLR camera is able to record high-quality images only because it includes an interchangeable lens that captures more light and has advanced optical technology that can render the minute details of the image.

2. Structure and coating of interchangeable lenses

How light is lost through reflection on the lens surface

There are numerous types of interchangeable lenses for digital SLR cameras—wideangle lenses, telephoto lenses, zoom lenses, and so on—used for different photographic applications. Camera lenses are constructed by combining a number of lens elements. Elements are combined to correct image distortion or deviation in color balance. Some interchangeable lenses for SLR cameras have 10 or more elements. Though picture quality can be improved by increasing the number of elements, there's no way to prevent reflection from reducing the quantity of light as light passes through the lens. Glass generally reflects 4 - 9% of the light at its surface. Since light passes through two surfaces (front and back) for a single lens, as much as 8 - 18% of the light is lost. The purpose of coating technology is to minimize this loss of light through reflection; coating has a major influence on lens performance. Coating is used not only on the elements of camera lenses but also on the lenses of eyeglasses and the windshields of cockpits of airplanes to reduce reflection and make objects easier to see through them.

New problems occur with the transition from film to digital cameras. When film is exposed to light, the light can be appropriately dispersed while minimizing reflection, since the surface of film is not like a mirror. With digital cameras, however, strong reflection occurs when light falls on the image sensor. The structure of digital cameras makes it easy for ghosts*1 and flare*2 to occur compared with film cameras. As a result, the coating technology for interchangeable lenses used on digital cameras need to provide an optical performance of greater precision than the antireflective technology used in the interchangeable lenses for film cameras.

How ghosts occur due to reflections from the image sensor

  • *1 Ghost: Light in the shape of a radial pattern, ring, or circle that occurs on an image as a result of repeated reflections inside the lens or camera when a photo is taken in strong light. Typical ghosts are in the shape of the aperture.
  • *2 Flare: Like ghosts, flare occurs when a photo is taken in strong light. Light scatters inside the lens and camera, reducing contrast, and sections of the photo may get a tint of white and colors may bleed.

3. "Nano Crystal Coat," Nikon's top-notch coating technology

Nano particles are arranged coarsely on the substrate and sublayers.
Structure of Nano Crystal Coat

The Nano Crystal Coat used on the camera interchangeable lenses is an adaptation of the nano particle coating that was initially developed for use in the projection lenses of Nikon's IC steppers and scanners. This ultra-low refractive index film is called "Nano Crystal Coat" as it comprises particles which are as small as several nanometers to 10-20 nanometers (1 nanometer is 1/1,000,000 of a millimeter). Although the term "Nano Crystal Coat" evokes an image of high density structure, the reality is completely the opposite—rather than being tightly arrayed, nano particles are arranged in a spongy construction with uniform spaces between the particles. This coarse structure—which is in complete contrast to the densely packed composition of existing coatings—provides the ground for lower refractive indices. The environment that resembles highly permeable paved roads makes it easy for light to pass through the lens.

Difference in refractive index between conventional coating and Nano Crystal Coat

The Nano Crystal Coat provides an extremely high preventive effect against reflections over a wide wavelength range by reducing the reflection of light that comes in perpendicular to the lens compared with conventional anti-reflection coatings. Furthermore, the Nano Crystal Coat exhibits unprecedentedly excellent effects against ghosts and flare that are caused by the light obliquely coming from the lens—a problem difficult to remove with conventional coatings. Its overwhelming effect has earned appraisal among professional photographers. Also, this technology is likely to be used in areas other than cameras and optical equipment as well. Since the Nano Crystal Coat can be widely applied to familiar optical products such as binoculars and fieldscopes, to the cutting-edge equipment essential for space development—and not just to glass but to plastic materials, too—it can produce stunning effects on the things around us. The "Nano Crystal Coat" is truly a new technology with extremely high potential.

Nano Crystal Coat

Conventional multi-layer coating

Posted June 2008