The Cokin Split Field filter means that you can focus very close to a subject & retain the same clarity for the background. This is achieved by placing a diopter (close-up lens) in one half of the lens frame. The other half has no lens so you can focus on the background object as normal while the diopter focuses on the close-up subject. By turning the filter you determine what is close & what is background. Cokin Split Field filters are available in 3 different 3 dipoter strengths, & this 111 is the weakest of the three at +1 dipoter.