4X 10X 20X 40X 60X 100X Biological Microscope Objective Lens Color Eraser Lens Features: Type: Microscope Objective Magnification: 4X/10X/20X(S)/40X(S)/60X(S)/100X(S+Oil) Mounting Dimensions: 20.2mm Standard RMS Thread Material: Precision Copper Core Tube Length: 160mm Covered Glass Standard Thickness 0.17mm Detailed bioscope information : 4X : Number of Openings (NA) 0.1; Operating Distance 18mm10X: Number of Openings (NA) 0.25; Operating Distance 7mm20X (S): Number of Openings (NA) 0.4; Working Distance 0.55mm40X(S) : Number of Openings (NA) 0.65; Working Distance 0.53mm60X (S): Number (NA) 0 .65; Operating distance 0.13mm100X (S+Oil): Number of Openings (NA) 1.25; Operating distance 0.13mm