This ARRI IFM FSND Full Spectrum Neutral Density 2.4 Filter is an 8-stop ND filter that fits into the Internal Filter Module (IFM) and goes behind the lens on an ALEXA XT, SXT, or Upgraded ALEXA Classic camera. As it is an FSND, it attenuates all wavelengths evenly, for consistent color when cutting between shots captured with a filter and without.
Behind-the-lens filtering has the advantage of reducing weight and avoiding the worry over veiling glare striking your filter.
This is a full spectrum neutral density filter. This means it evenly attenuates light at all frequencies, providing a neutral color balance no matter what the density of the filter.
Using this filter with your ALEXA XT, SXT, or upgraded Classic requires the use of the IFM shim for best lens performance.