This article describes the recommended aperture sizes for color measurements of screened samples.
There is a correlation between the lineature of printed samples and the aperture of a spectrophotometer that will give you error-free measuring. The following aperture sizes are recommended:
1.5 mm instrument, for 2mm patches, for screening of 175 l/inch, 69 l/cm or above
2 mm instrument, for 3 to 5 mm patches, for screening of 133 l/inch, 52 l/cm or above
4 mm instrument. for 5 to 6 mm patches, for screening of 65l/inch, 26 l/cm or above
6 mm instrument for large patches (e.g. in packaging)
You notice that it is not recommended to measure samples with a ruling less than 65 LPI with spectrophotometers like a X-Rite i1 which has a 4.5mm aperture.
The eXact has different Aperture sizes to meet all applications: With a choice 1.5, 2, 4 or 6 mm, the instrument can measure across a range of application in print and packaging. For each eXact aperture size, the target window is 1mm (radius) larger than the spot measurement area size. This 1 mm over illumination of the measurement area is required by ISO5/4. The White area around the patch does not influence the measurement data, but does require the operator to center the measurement sample in the target window opening.