Polarization Filter xrite 518

[cosmo]

hi,

Ive just put a polarization filter in our xrite 518, according to ISO 12467-2 thats what needs to be used, but it reads a much higher density now, eg, what was reading 1.45 with non polar now reads 1.7 with polarization filter, i guess now this means i have to go back and redo my density settings with press run and a spectro to get correct LAB reading, is there any reason they read so much higher?

 

[meddington]

Ive just put a polarization filter in our xrite 518, according to ISO 12467-2 thats what needs to be used, but it reads a much higher density now, eg, what was reading 1.45 with non polar now reads 1.7 with polarization filter, i guess now this means i have to go back and redo my density settings with press run and a spectro to get correct LAB reading, is there any reason they read so much higher?

The actual CIELab aims values in ISO 12647-2 are defined without polarization, so if your dry solid Lab values are measuring within tolerance using your un-filtered spectrophotometer (D50, 2 degree, 0/45), the filtration on the densitometer is not relevant with regard to the solids. So you could verify solid Lab with the spectro, then establish custom density targets using whatever status and filtration you desire...as long as your consistent.

ISO 12647-2 does specify the use of status E with polarization for established TVI aim values, however also notes that without polarization, and with status T unfiltered should give you the same values with the exception of yellow which should be approximately 2% less.

The primary benefit of the polarization filter is less differences between wet and dry measurement values. However, the benefits are also a bit dependent on the substrate and ink properties (absorption, surface roughness as the inks dry, etc.). Moreover, the difference between wet and dry solids is often visual, so with a pol. filter, your basically pretending the difference doesn't exist. So although pol. filters could make establishing target densities independent of drying time, I personally don't recommend their use.