Apertures available for eXact:

There are 4 available apertures for the eXact handheld; NOTE: These are not changeable in the field.

1.5mm, 2.0mm, 4.0mm, 6.0mmThere are 4 available apertures for the eXact handheld; NOTE: These are not changeable in the field.

Aperture & target window size

For each eXact aperture size, the target window size is 1 mm (on 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. 


Available aperture sizes:

Aperture Size	Measurement area size	Opening in target window	Recommended patch size	Screening Range
1.5mm	1.5mm	3.5mm	2mm - 3mm	175 lines/inch or 69 lines/cm or above
2mm	2mm	4mm	3mm - 5mm	133 lines/inch or 52 lines/cm or above
4mm	4mm	6mm	5mm - 7mm	65 lines/inch or 26 lines/cm or above
6mm	6mm	8mm	7mm or larger

It is always recommended to use the largest aperture size possible.



The illustration below shows how this minimum measurement area appears in relation to the target window opening.

The black circle represents the target window opening.

The white circle represents the actual measurement area (which equals the aperture size).

The magenta square represents the minimum suggested patch size.

This can be used as a guide for operators when placing the instrument optics over patches which do not completely fill the target window opening.