Highlights:

The HOYA color correction filters, BLUE COOLING and UMBER WARMING, are designed to adjust the white balance of the image.

The BLUE COOLING filters raise the overall color temperature value and are used to correct reddish or orange hues when shooting outdoors, or indoors under tungsten or fluorescent lighting.

Technology

The BLUE COOLING series features C2, C4, C8 and C12 gradation, which refer respectively to a mired shift of -20, -40, -80 and -120.

In other words, as seen in the transmission graph, the BLUE COOLING series reduces orange and reddish light entering the lens, therefore indirectly enhancing blue colors. The lower the mired value, the less orange and red light enters the lens and the stronger the cooling effect.

It is possible to combine various BLUE COOLING filters to achieve different values, which allows photographers to achieve almost any desired color correction.