The Leitz Wetzlar NPL 16/0.40 P 170/- is a classic, high-quality German microscope objective produced during Leitz’s 170 mm mechanical tube length era (primarily from the 1960s to mid-1970s).

Decoding the Inscription

• NPL (Normal-Plan / Near-Plan): Indicates field-flattening optics designed to keep the image sharp across the field of view up to approximately an 18 mm field number (FN).
• 16: 16x Magnification. This intermediate magnification power bridges the gap between low-power survey lenses (4x/10x) and medium-power detail lenses (20x/40x).
• 0.40: Numerical Aperture (NA = 0.40). This is quite high for a 16x lens (standard 10x lenses are usually around 0.25, while 20x lenses hover around 0.40–0.45). It provides good light gathering and resolving power for its magnification.
• P (Polarization): Specially selected, strain-free optics designed for polarized light microscopy (petrography, mineralogy, metallurgy, or material analysis). Lenses marked P or POL prevent unwanted birefringence inside the glass, ensuring clear extinction under crossed polarizers.
• 170: 170 mm Mechanical Tube Length. Calculated for standard black-frame and early gray-frame vintage Leitz stands (such as the Ortholux, Dialux, Laborlux, and Orthoplan).
• - (Dash): Insensitive to cover glass thickness. Can be used either with or without a glass coverslip (or used for incident light / metallurgical applications) without spherical aberration degrade.