ISO 5-2:2009 specifies the geometric conditions for measuring ISO 5 standard diffuse and ƒ/4,5 and ƒ/1,6 projection transmittance densities.

ISO 5 standard diffuse density is primarily applicable to measurements of photographic images to be viewed on a transparency illuminator, or viewing box, to be contact printed, or to be projected with a system employing diffuse illumination.

ISO 5 standard projection density is primarily applicable to measurements of photographic images to be projected with systems employing optical condensers.

Although primarily intended for the measurement of photographic images, the densitometric methods specified in ISO 5-2:2009 are often applied to optical filters and other transparent materials.