Carl Zeiss 2.5X plan achromat microscope objective. The Zeiss catalog number is 46-01-10. It has a working distance of 8.9mm and n.a. of 0.08.  All glass surfaces are free from element separations, dust, scratches, and fungus. This objective is intended to be used on 160mm tube length Zeiss microscopes such as the Standard, Universal, IM and Photomic. It will work equally as well on microscopes with this 160mm TL from Leitz, Nikon and Olympus. Thank You For Looking!