The focal point of the device lens is 150 mm (TP31-IR121) or 762 mm (TP31-IR301) from the beam exit opening. There the measuring spot has a diameter of 12.5 mm respectively 25.4 mm, resulting in a ratio of D:S of 12:1 or 30:1. The size of the measuring spot corresponds to 90 % of the measured energy. The TP31-IR301 therefore also allows accurate measurements of small surfaces from further distances.

The focal point of the device lens is 150 mm (TP31-IR121) or 762 mm (TP31-IR301) from the beam exit opening. There the measuring spot has a diameter of 12.5 mm respectively 25.4 mm, resulting in a ratio of D:S of 12:1 or 30:1. The size of the measuring spot corresponds to 90 % of the measured energy. The TP31-IR301 therefore also allows accurate measurements of small surfaces from further distances.