The Tiffen 4 x 4" 81A Light Balancing Filter helps to decrease the color temperature by 200K in order to warm the image slightly in order to match the color quality of illumination. When using an 81A filter, you will be able to attain 3200K balance when the prevailing light source is 3400K. The warming effect of this filter requires a 0.3-stop increase in exposure for normal results. This filter is made using ColorCore technology, a process that involves laminating the filter substrate between 2 pieces of optical glass and grinding flat to a tolerance of 1/10,000th of an inch. It measures 4 x 4" / 101.6 x 101.6mm. Light balancing filter decreases color temperature and provides a warming effect. Subtracts 200K in order to attain 3200K color balance from 3400K illumination. Filter factor of 1.3 requires a 0.3-stop increase in exposure. Light Balancing Filters 81 Series The 81 series filters are useful with daylight corrected film in cool light conditions. As letters advance, density and warmth increases. 81A, 81B, 81C, & 81EF Creates warmer tones and brighter colors on overcast days or when shooting with electronic flash Great for improving flesh tones 81A converts tungsten 3200 K film to 3400 K lighting.