The Leica 506003 is a high-performance microscope objective designed primarily for research-grade biological and clinical applications. Breaking down the markings and specifications on the barrel provides a clear understanding of its capabilities:

Technical Specifications Breakdown

• PL FLUOTAR (Plan Fluorite): This indicates the optical correction class. Fluorite (or semi-apochromatic) lenses offer excellent color correction for multiple wavelengths and high excitation light transmission, making them exceptional "photon collectors" for fluorescence imaging. The PL (Plan) designation means it features flat-field correction, ensuring the image remains sharp and in-focus from the center all the way to the edges of the field of view.
• 20x: The optical magnification factor.
• 0.50: The Numerical Aperture (NA). For a 20x dry objective, an NA of 0.50 is quite high, yielding excellent light-gathering capabilities, a shallow depth of field, and crisp resolution.
• ∞ (Infinity Corrected): The infinity symbol means it is designed for infinity-corrected optical systems. It requires a tube lens inside the microscope body to form the intermediate image, allowing for the insertion of optical accessories (like polarizers or fluorescence filters) into the parallel beam path without introducing aberrations.
• 0.17: Refers to the standard cover glass thickness (0.17 mm) that this objective is optimized to image through. Using it without a coverslip, or with one of the wrong thickness, will introduce spherical aberration and degrade image quality.
• B (Brightfield / Band Ring): Typically denotes the standard mechanical/optical grouping or the specific color code band (often a yellow/greenish scheme for 20x) utilized by Leica for quick visual identification on a nosepiece.

Core Applications

Because of its high transmission capabilities, particularly in the near-UV and visible spectrum, this objective is highly versatile and commonly used for:

• Fluorescence Microscopy: Excellent for detecting faint fluorescent signals.
• Brightfield (TL-BF): Standard high-contrast tissue and cell imaging.
• Differential Interference Contrast (DIC) & Polarization: It serves as a great base lens for contrast-enhancement techniques if paired with the correct prisms/polarizers.

 Compatibility

With the 506003 part number, this objective features Leica's older standard M25 thread size and a 60mm parfocal distance. It is directly compatible with Leica's DM series (e.g., DM4000, DM5000, DM6000, DMI6000) and older infinity-corrected upright and inverted research microscopes.