What is HD Coating?

HD Coating is a new-generation, multi-layer lens-coating technology, developed to provide better-quality optical characteristics in a greater number of lens products. It was designed to satisfy the demand for higher lens performance that is required by advances in digital cameras.

Comparison of the reflectance of multi-layer coatings

With the application of a state-of-the-art multi-coating process completely different from the conventional one, HD Coating provides a coating layer thickness and anti-reflection performance that is close to theoretical design specifications. A lens surface treated with HD Coating assures reflectance that is less than 50% that of conventional multi-layer coatings.

Unevenness of reflectance with
conventional multi-layer coatings
Unevenness in reflectance of HD Coating

The graphs above show the optical performance of samples selected from each category, after treatment with 10 layer-forming processes. As you can see, HD Coating samples show extremely high layer-forming precision and extremely low discrepancy in reflectance. Since reflectance curves are almost identical at different wavelengths, the HD Coating graph demonstrates optical characteristics which deliver ideal color balance.

The history of PENTAX lens coating technologyA pioneer of multi-layer lens coating technology

In 1971, PENTAX made an innovative advancement in optical technology by increasing the number of coating layers from two — the norm at the time — to as many as seven.

Since then, lenses with the prefix “smc PENTAX” have been preferred by many photo enthusiasts. With the advancement of production technologies and camera digitalization, PENTAX’s multi-layer coating technology has continued to evolve to meet the demands of the times.

Development of Aero Bright Coating boasting the highest anti-reflection performance

PENTAX later developed Aero Bright Coating, which provided excellent transmissivity through a wider range of wavelengths and outstanding anti-reflection performance, by applying a silica aerogel coating layer with a uniform porous structure over a regular multi-coating.

Aero Bright Coating was first introduced in 2009 to the smc PENTAX-DA★ 55mm F1.4 SDM, and helped to further improve the optical characteristics of high-performance lenses.

The birth of higher-performance, more cost-efficient HD Coating

Even though Aero Bright Coating had superior anti-reflection performance, its nano-order, porous structure has a very delicate coating structure that can be easily damaged by abrasions or scratches. Because of this, its application was limited to a small selection of lens surfaces. It also wasn’t suited for mass production because of restrictions faced in the production process. It therefore could be applied only to rather high-priced models.

To resolve this setback, PENTAX set out to further upgrade its multi-layer coating technology — something indispensable in optical glass — and achieve an optical performance close to that of Aero Bright Coating. Compared with a conventional seven-layer coating applied by a vacuum evaporation process, the new HD Coating forms an eight-layer coating with a uniform layer thickness, created by a high-precision, ion-assisted evaporation process. This is further reinforced by a ninth coating added to the outermost layer by a vacuum evaporation process.

Comparison of unevenness in layer thickness

The graph above demonstrates the unevenness in coating layer thickness generated by different coating processes. The ion-assisted evaporation process used for HD Coating has a larger number of samples with zero deviation than the vacuum evaporation process. It also shows a smaller deviation from average thickness.

Because this new coating process minimizes the unevenness in layer thickness created during the coating process, it can improve the overall optical performance of nine-layer HD Coating. Thanks to a higher packing density, it also forms an extremely solid coating layer, making it possible not only to improve lens quality, but also to enhance its applicability across a wider range of lens surfaces and imaging products.

Comparison of reflectance by lens coating

HD Coating demonstrates exceptional anti-reflection performance, far superior to that of the conventional multi-layer coating but also close to Aero Bright Coating — PENTAX’s top-grade lens coating — in the visible ray range (400 to 700 nanometers).

PENTAX intends to expand the HD PENTAX-series lens lineup featuring high-performance, cost-efficient HD Coating.