Type:Microscope achromatic Objective lens Magnification: 4X/10X/20X(S)/40X(S)/60X(S)/100X(S+Oil) Mounting size :20.2mm Standard RMS thread Material:Precision Copper core Tube length : 160mm standard thickness of cover glass 0.17mm for Biological microscope 4X :Numerical Aperture (NA) 0.1; working distance 18mm 10X: Numerical Aperture (NA) 0.25; working distance 7mm 20X (S): Numerical Aperture (NA) 0.4; working distance 0.55mm 40X(S) : Numerical Aperture (NA) 0.65;working distance 0.53mm 60X (S): Numerical Aperture (NA) 0.65; working distance 0.13mm 100X (S+Oil):Numerical Aperture (NA) 1.25 ;working distance 0.13mm.