The Leica PL FLUOTAR 40x/0.70 ∞/0.17/D (Article/Part Number: 506004) is a professional-grade microscope objective lens designed for research-grade Leica infinity-corrected microscope systems (such as the DMR and DM series).

Optical and Technical Specifications

• PL FLUOTAR (Semi-Apochromat): "PL" stands for Plan, indicating excellent field flatness across the entire field of view, making it ideal for both visual observation and digital imaging. "FLUOTAR" specifies that it utilizes fluorite glass formulations. These provide superior chromatic and spherical aberration correction compared to standard Achromat objectives, delivering highly accurate color rendering and excellent contrast.
• 40x Magnification: Provides a medium-to-high magnification level, suitable for observing cellular structures, histology sections, and microorganisms.
• 0.70 Numerical Aperture (NA): The NA of 0.70 dictates the light-gathering capacity and resolving power of the objective. For a dry 40x objective, 0.70 is a high numerical aperture, offering a resolving power down to approximately 0.4 microns under standard visible light.

• ∞ (Infinity Corrected): This symbol signifies that the objective is designed for an infinity-corrected optical system. Light leaves the objective as parallel rays, allowing optical components (such as sliders, filters, or beamsplitters) to be inserted into the parallel light path without introducing optical aberrations.
• 0.17: Indicates that the objective is optically corrected for use with a standard 0.17 mm thick glass coverslip (No. 1.5). Deviations from this coverslip thickness can cause spherical aberration and degrade image sharpness.
• D (Dry / DIC Compatibility): * The "D" stands for Dry, meaning it operates with air between the objective tip and the coverslip (no immersion oil or water required).
• In Leica's naming convention for this era, the letter classification (specifically D) also indicates its compatibility group for Differential Interference Contrast (DIC). It determines which specific Wollaston/Nomarski prism (often designated as a "K" or "D" type prism in the condenser/slider) matches the objective's back focal plane to achieve proper DIC contrast.

Mechanical Properties

• Threading: Typically utilizes Leica’s standard M25 x 0.75 metric thread pattern, which is wider than standard RMS threading.
• Parfocal Distance: Designed to match Leica's standard 45mm parfocal distance, meaning the sample remains mostly in focus when switching between this and other calibrated Leica objectives on the nosepiece turret.

Common Applications

Due to its high contrast, color correction, and flat field, this objective is commonly used in:

• Transmitted light brightfield microscopy.
• Fluorescence microscopy (due to the high UV/visible light transmission properties of Fluotar glass).

• Differential Interference Contrast (DIC) microscopy.