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HRT - High Resolution & Transmission

The Hoya HRT filter class is an outsider in the world of photography. Actually it's not a class, it's more a type of filter. It was developed after intensive research and development. In the HRT filter, two filtering effects have been merged: polarizing and UV filtering.

Polarizer

The polarizer in the HRT consists - like with all polarizers - of a polarizing film between planes of optical glass. All polarizers reduce the light transmission, namely the polarized component from a certain direction of the ambient light. Consequently the photographer needs to use longer exposure times or wider apertures. That might be undesirable in many situations. It is for that reason that Hoya developed the HRT. The HRT's polarizing film is thinner than an ordinary one and but still induces all the properties of a polarizer, yet it lets more light rays pass. The transmission of a HRT is 97%, albeit that this percentage greatly depends on the angle towards the light source you use the polarizer for.

UV filter

The second function of the polarizer is the effective exclusion of UV light. The front plane of the polarizer is actually a fully functional UV filter. There are two advantages of this combination. When using a polarizer objects in the shadow parts of your image often show a blueish tinge. That's a natural effect, but still, it doesn't look good. The UV filter of the HRT diminishes this blue shade.
Secondly, every polarizer film tends to ware out as a result of UV radiation. So here the UV filter comes to the aid also, it brings down the penetration of UV light rays into the polarizer film layer. As a matter of fact, the polarizer film of a HRT film is thinner than the one you find in an ordinary polarizer, but due to the extra UV filter it will last longer!

Mount

Hoya's HRT's have a remarkable thin mount of 5,75mm. It makes them very well suited for (ultra) wide lenses. Only Hoya's HD and Pro1D class filter classes offer thinner rings.