The first step is to determine what type of filter is required for the application. The basic types of filters are shortpass, longpass, bandpass, dichroic, notch, and neutral density. Each type of filter has unique characteristics that lend better to one application or another. The second step is to determine what wavelengths are required, as filters are defined by what part of the spectrum they pass or do not pass. For instance, an UV Cut-Off (or Longpass) filter is designed to pass both the visible and IR portions of the spectrum, but block (or "cut") the UV portions of the spectrum.