This is a narrowband filter matched to the laser wavelength and permanently installed in the AR4000 device in front of the photodiode.

The filter blocks 96% of light to which the 4000's detector element is sensitive. It is availabe for all three Acuity laser rangefinder models, the LIR, the LV and the RET.

The filter is installed internally in the AR4000 at manufacture and the focusing of the collection optics is adjusted for it, so retrofitting the Optical Filter carries additional charges.