Figure 1 shows an instrument that is being successfully marketed worldwide.  Its visible target measurement area can be easily varied from 500 microns to 10 meters by simply sliding the outermost barrel in and out.

Vario-Zooom Infrared Temperature Sensor

Figure 1
Vario-Zooom Infrared Temperature Sensor

The variable focusing operation changes the optical gain of the instrument by less than 1 percent, making the accuracy essentially independent of focus. 

The illuminated variable Field-of-View ranges from 2 to 40.   The illuminated spot being measured on the target is variable from 1.0 millimeter or less to 30 meters or more.  Of course, the illumination intensity fades out at wide angles or large spots, depending on the ambient lighting conditions. 

The working distance is from 2 cm to 100 meters.

The LED light source has only 2000-1 of the power density of a laser, so it is perfectly safe, and does not need the CAUTION! Labels mandated by the FDA for lasers, which can burn the retina if mishandled.