In outdoor photography, not only cameras but also the lenses are required to endure demanding environmental conditions. The dustproof / weather resistant, AW-type (All Weather) lens has been developed by overcoming the issues inconsistent with high water-proof performance, such as the requirement of an air vent structure for its extensional motion, and a light operational feeling. Each part is sealed so that you can freely take photos even in rain, mist, or at locations prone to dust.
Aero Bright Coating is our own lens coating technology developed from nanotechnology. It applies a silica aerogel coating layer with uniform porous structure over a regular multi-coating layer. This traps low-refraction air between stable silica nanoparticles for enabling a coating with super-low refraction rate and high transparency. The coating has greatly reduced surface reflection. In addition, using a new super-low refractive index layer formation process, we have developed Aero Bright Coating II, which enhances low-reflectance properties.
Typically, multicoatings are formed by using vacuum deposition to apply a thin layer to the lens surface. However, this fabrication process also presents problems because of the difficulty in increasing the density of the coating film and the variation in refraction rates and film thicknesses. PENTAX's solution to these problems was our HD Coating, using PENTAX's exclusive special fabrication process, where high-density film is applied with high precision at the nanometer level. This enables the reliable formation of the designed film thickness for a dramatic reduction of the reflection rate (up to 50% compared to conventional coatings) over the entire visible light range. It is also effective in reducing ghosting and flare. Moreover, the film coating has an extremely high hardness for providing superior durability.
The refraction rate of glass varies depending on the light wavelength. For this reason, because natural light consists of light of various wavelengths, this light fails to converge to a single focal point when passing through a lens. When an image is enlarged on a computer screen, you can sometimes see purple blurring around images of red points, for example. This is called chromatic aberration. In typical lenses using optical glass, this is difficult to correct as the focal length becomes longer. To minimize the chromatic aberration, PENTAX uses extra-low dispersion (ED) glass, extraordinary-low dispersion glass, and high-refraction low dispersion glass, all of which have low spectral dispersion of light beams. The appropriate glass types are used for attaining exceptional imaging performance. HD PENTAX-D FA★70-200mmF2.8ED DC AW features four extraordinary-low dispersion glass elements, two extra-low dispersion (ED) glass elements, and two super ED glass elements, which have optical properties similar to fluorite and assure lower light dispersion and more effective compensation of chromatic aberration. As the result, this lens produces brilliant, high-contrast images with edge-to-edge sharpness, while effectively compensating chromatic aberration over the entire zoom range.