General Hoya filters include the ultraviolet (UV) filters, which absorb ultraviolet rays avoiding the hazy effect sometimes found in outdoor photography; skylight filters, which help to reduce the blue shades frequent in outdoor photography; neutral filters, which are transparent and only used to protect lenses from dirt and scratches; and the polarizing filters, which increase color saturation and contrast between clouds and sky in sunny days and remove glare on water, metallic and glass surfaces. Hoya also produces a hybrid filter, which is a combination of a UV and a polarizing filter.
Starbursts, close-ups, multi-images and fuzzy images are possible effects when using the right filter. Hoya produces more than 30 special effect filters, including the dual-image filter, which allows the same person to appear in both sides of the same picture; the star-six filter, which produces six-pointed light flares; the color multivision filter, which produces multicolored and multifaced images; the spectral cross filter, used in portrait to create a soft-focus effect; and the sepia filter, used to give shots the sepia tones common in old photography.
As the name suggests, Hoya colored filters have tinted glass and are used to correct light tones, as well as in creative shots. FL filters are pinkish and used in fluorescent lighting, while the 80 and 82 series are blue and the 85 series are orange. Other colored Hoya filters include the K2 or yellow filters, which increase the contrast in the skies; the G orange filters, which increase the contrast between yellows and reds; the 25 A red filter, used to create dramatic contrast effects on skies; and the XO and X1 green and yellow filters, often used in black-and-white outdoor photography.
Hoya HD UV and polarizing filters are made with hardened optical glass, which is more resistant to scratch and breakage, when compared with the general filters. Hoya Pro1 digital filters are a series of multicoated professional filters, including UV; polarizing; ND4 and ND8, which are used to reduce the light that reaches the camera; star-4 filter, which creates special star effect on light flares; close-up number 3, used to increase the details in macro photography; and softon-A, which creates low-contrast images.