Tiffen 6.6″x6.6″ 81EF Light Balancing Filter is useful with daylight corrected film in cool light conditions. 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 6.6 x 6.6″ / 167.6 x 167.6mm.Light balancing filter decreases color temperature and provides a warming effect.Subtracts 650K in order to attain 3200K color balance from 3850K illumination.Filter factor of 1.5 requires a 0.6-stop increase in exposure.Creates warmer tones and brighter colors on overcast days or when shooting with electronic flashGreat for improving flesh tones81A converts tungsten 3200 K film to 3400 K lighting