A B&W 52mm FL-D Slim Glass filter is used when you wish to correct for the greenish tone that appears when shooting daylight film under general purpose fluorescent lighting. This orange colored filter blocks the blue and blue-green portion of the visible spectrum up to approximately 520nm. It reduces the excessive sensitivity of color infrared films for this spectral range, helps avoid blue tint and differentiates colors more evenly.
Fluorescent lamps burn at many different temperatures and often require more demanding filtration for exact results. For specific filtration and professional use, it is strongly recommended that a color temperature meter be employed along with Color Correction filters (i.e.CC30M) when shooting under fluorescent lighting. This is the only proven way to achieve exact color correction.
NOTE: The FL series of filters alone does not always guarantee 100% correct color balance when shooting under fluorescent lighting. They are general purpose filters intended for moderate correction and will not, by themselves, necessarily provide perfect color rendition. An FL-W filter is used to balance daylight film under warm white or white type fluorescent lamps. An FL-B filter is used to correct the color balance when shooting tungsten film under fluorescent lighting.
B&W slim filters are for wide-angle lenses and are 3mm thick. They do not have a front thread.