An auto-ranging densitometer is disclosed for determining the density of a test sample, wherein the densitometer includes a photodetector and an amplifier circuit adapted to produce an output signal proportional to intensity of light on the photodetector. The amplifier circuit has multiple gains that successively increase in an approximately 2:1 ratio increment. An analog to digital converter is adapted to convert the output signal of the amplifier circuit to digital format. A density signal generator circuit is adapted to receive the output of the analog to digital converter, whereby density resolution non-uniformity is minimized due to small gain increments such that the analog to digital converter needs deal with less extreme variations in density resolution.