When capturing directly against light or lamps, reflections may occur as small blue/green spot/circles.
This may be caused by internal reflection between the IR cut-off filter and the image sensor. The best solution is to change the angle of the image slightly and adjust the angle of incidence.
In rare cases, Phase One can provide a camera back without an IR cut-off filter to avoid reflections. In that case the IR cut-off filter in front of the lens is required.