I use Cycles engine of Blender (V 2.82) to obtain the strength and distance (light-objects-camera) of each pixel, for some applications of Radar signal processing, as the papers:
 A simple radar simulation tool for 3D objects based on blender: A simple radar simulation tool for 3D objects based on blender | IEEE Conference Publication | IEEE Xplore
 General Purpose Radar Simulator based on Blender Cycles Path Tracer: 1570649487.pdf (sbrt.org.br)
The radar processing is not important here, the matters are the distance and amplitude information of pixels.
The issues I met are:
(i) set the light source and camera at one location, then a target model at a distance of around 8 meters. In principle, the distance matrices should be 16 meters (pixels with target) and 0 (pixels without target). I found most of the values are correct, however, there are some other values, 3 meters, 5 meters, and also even some big values like 25, and 50 meters.
I guess those small values like 3 meters are from the pixels of the target bounder. The big values may be due to the sharp parts/points of the target, or the singularity of Blender, I am not sure.
Q (1): I want to ask, can I change some settings of Blender to obtain accurate distances?
(ii) for the same scenario, I only move the location of the camera by a small distance, for example, 0.5 mm, in principle, the changes in the distance matrix should be less than 0.5 mm; however, I found changes for meters happen in some pixels.
Q (2): Is Blender sensitive and accurate enough to catch the distance differences between two cameras, whose locations are only 0.5 mm?
Q (3): Where can I find some documents/resources on what’s the distance rendering accuracy of Blender?