Nikon CF Achromat 40X Long Working Distance (LWD) Microscope Objective.  This objective's cosmetic condition is not the best as can be seen in the photograph. Someone used a pair of pillars around the nose ring to remove it from a nosepiece. I sent the objective to Nikon several years ago for repair, but they were out of the chrome rings, so they just polished it and left it as you see it.  It will fit the Nikon Diaphot TMD and TMS of 160mm tube length  inverted microscopes. One of the virtues of this lens is that it will work extremely well on upright compound microscopes, and is ideal for looking at pond water specimens because of the variable coverslip thickness and it is Long Working Distance. It will work very nicely with other manufacturers such as Olympus, Zeiss and Leitz.  This is an CF Achromat Brightfield Lens with coverglass correction collar,  capable of correcting for thickness of 0 mm to 2.0 mm. and the numerical aperture is (n.a.) 0.55. These lens is used but in excellent mechanical and optical condition with all glass being free from fungus, dust, scratches or element separation. The correction collar moves smoothly.   Thanks for looking.