The Filter Wheel 3 Neutral Density/ 81A Color Conversion Filter from Tiffen controls the bluish coloration that affects daylight film. It can also remove excessive blue from the effects of electronic flash.
It's Autumn. The clouds are low hanging and the sky is "patchy blue". You've gone for a ride upstate to the mountains and the light in open shade is bluish. A photo taken of your girlfriend with daylight balanced film leaning against the side of a barn will yield bluish tones that she might not find particularly flattering. An 81A filter will replace some of the yellow missing from the image and bring her skin tones back to a more appealing level.
A Solid Neutral Density filter from Tiffen has several uses and offers the possibility to achieve otherwise unachievable results. It enables the shooter to adjust exposure without affecting color balance. ND filters appear gray and reduce the amount of light reaching either the sensor of a digital camera or the film plane of a traditional film camera.
Neutral Density filters are used to create some unusual special effects such as capturing the "blur" of the rippling water of a waterfall or the swirling effect of city traffic. Since they allow the use of slower shutter speeds in bright light, it becomes possible to create these special effects that would normally not be possible to capture without the filter. And since they can also help to control your depth of field, they permit you to shoot at wider apertures. Ultimately, their value is in helping to prevent bright, overly washed out images shot in bright light.
Tiffen's ColorCore glass is produced through a process that entails permanently laminating the filter material in between two pieces of optical glass that are ground flat to tolerances of a ten-thousandth of an inch, then mounting them in precision aluminum rings.