The Tiffen Cokin P ND 0.9 Glass Filter enables the shooter to adjust exposure without affecting color balance. Neutral density filters are available in various stops to suit individual situations.
Determining which neutral density filter yields ideal results for any given lighting situation takes knowledge, experience, and a collection of such filters. Choose the filter strength that adjusts the lighting to stay within the exposure latitude (greatest difference between bright/dark values) that still shows details in both the digital or film medium in use.
Speaking generally, the 2-stop value (ND 0.6—the filter's clear portion allows 4x more light to pass vs. darkest portion) effectively compensates average situations.
When more precise lighting control is required, Tiffen also makes a series of graduated neutral density filters. These filters permit better exposure balance between bright skies and darker foregrounds or vice versa.