The Tiffen 4 x 5.65" 81D Light Balancing Filter reduces colour temperature by 500K to slightly warm the image to match the colour quality of the lighting. By using an 81D filter, you can achieve a 3200K balance when the dominant light source is 3700K. The warming effect of this filter requires a 0.6-stop increase in exposure for normal results.nnThis filter is manufactured using ColorCore technology, a process that laminates the filter substrate between 2 pieces of optical glass and grinds it flat to a tolerance of 1/10,000th of an inch. It measures 4 x 5.65" / 101.6 x 143.5 mm.nnn- Light balancing filter that reduces colour temperature and provides a warming effect.n- Subtracts 500K to achieve a 3200K colour balance from 3700K lighting.n- Filter factor of 1.5 requires a 0.6-stop increase in exposure.nnnTechnical specificationsnn