With +5 diopters, the NL 5 serves for the seamless extension of the range provided by the NL 3 close-up lens on a 35mm main lens (up to appr. 1:3.5). If you can tolerate a small gap after the NL 2 close-up lens on a 50mm main lens (appr. 1:4.4 to 1:4), then you enter a little further into the macro range with the NL 5 instead of the NL 4 (up to appr. 1:2.6).
NOTE: B+W close-up filters (diopters) are a single element design. For two element options, check the Century brand achromatic diopters for HDV/DV and Broadcast.