Photomicrograph of trans-illuminated human red blood cells (erythrocytes) made at a magnification of 500 diameters using a solar microscope designed by the French photographic inventor and experimenter Auguste-Adolphe Bertsch (1813-1870). He is considered to be a pioneer in photomicrography. Using the sun as the light source, the microscope was able to create efficient bright-field illumination, reducing exposure times.