FITC/RSGFP/Fluo 3/DIO Acradine orange(+RNA) set (BA410E, AE31E)

This refers to the magnification factor of a single microscope lens. A lens with the number 40 is referred to as a scale of 1:40 or simply a factor of 40 times. If you multiply the lens factor by the eyepiece factor, you get the magnification.