Ssu Iron Microscope 10x Objective Lens Description: Objectives for brightfield, darkfield and phase contrast observation Magnification / Numerical Aperture • 10X Optical Correction Negative Phase Contrast. Flat field correction for 22mm F.N., planachromatic spherical and chromatic corrections. Mechanical tube length IOS (infinity-corrected tube length) Cover Glass Thickness 0.17 mm Working Distance • 10X W.D. 10mm