50mm achromatic doublet lens 800mm focal length

Product Description

Premium US-Manufactured Visible Achromatic Doublet Lens – 50mm Diameter, 800mm Focal Length, AR-Coated – Ready for Immediate Use

A precision-engineered cemented achromatic doublet lens from a reputable US manufacturer, delivered in pristine, ready-to-use condition. With a 50mm clear aperture, 800mm effective focal length (f/16) , and broadband anti-reflection coating optimized for the visible spectrum, this lens delivers exceptional color correction and diffraction-limited on-axis performance—ideal for telescope objectives, beam collimation, and precision imaging applications.

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🔍 Key Specifications:

• Diameter: 50 mm (precisely ~50.8 mm standard)

• Effective Focal Length (EFL): 800 mm (f/16 focal ratio)

• Design: Biconvex cemented achromatic doublet

• Edge Thickness: ~7.5 mm total

• Glass Types: N-BK7 (crown, positive element) + N-SF5 (flint, negative element)

• Coating: Broadband VIS AR coating – <0.5% reflectivity, >98% transmission per surface (400–700 nm)

• Orientation Mark: Arrow etched on edge – points toward more strongly curved (higher power) surface

• Condition: Pristine – no scratches, chips, or delamination

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✅ Condition & Notes:

• Condition: Excellent – Like New / NOS Quality

• Optical Surfaces: Absolutely clean – no coating defects, haze, or cleaning marks

• Cement: Perfect edge bond – no separation, yellowing, or stress birefringence

• Markings: Professional edge arrow for correct orientation

• Includes: Lens only – no mounting cell or hardware

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⚙️ Optical Design Excellence:

🔬 Premium Glass Pairing: N-BK7 + N-SF5
This classic achromatic combination offers:

• Superior chromatic correction – brings red and blue to common focus

• Reduced spherical aberration – f/16 design is exceptionally forgiving

• Excellent transmission from 400–700 nm

• Thermally stable – minimal focus shift with temperature

📏 Long Focal Length Advantage:
The 800 mm EFL at f/16 provides:

• Diffraction-limited on-axis performance – aberration-free even at full aperture

• Forgiving tolerances – ideal for first-time telescope makers

• Comfortable eye relief in visual astronomy applications

💎 Broadband AR Coating:

• <0.5% reflectivity across 400–700 nm

• >98% transmission per surface – maximizes throughput

• Durable hard coating – resistant to cleaning and environmental exposure

🎯 Orientation Marking:
The etched arrow follows standard optical convention – points toward the more strongly curved surface, which should face the longer conjugate (incoming parallel light) for minimum spherical aberration.

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🛠️ Applications & Uses:

🔭 Telescope Objective – Planetary & Lunar Excellence:
The 50mm f/16 achromat is a classic refractor objective configuration:

• Minimal chromatic aberration – false color virtually invisible

• Sharp, high-contrast views of the Moon, Jupiter, Saturn, and double stars

• Wide-field capability with low-power eyepieces

• Perfect starter scope for amateur telescope makers (ATM)

• Ideal solar projection (with proper filtration) – safe, detailed white-light views

💫 Beam Collimation & Expansion:

• Collimate divergent sources (laser diodes, LEDs, fiber outputs) over long working distances

• Beam expander output lens – low divergence, minimal wavefront error

• Alignment telescope objective – precision autocollimation setups

🔬 Imaging & Relay Optics:

• Low-distortion focusing for machine vision systems

• Relay lens in microscopy extensions or periscopic viewers

• Tube lens for infinity-corrected microscope objectives

📷 Projection & Magnification:

• Slide or enlarger lens – color-critical reproduction

• Solar projection – detailed white-light Sun viewing

• Large-format magnifier – distortion-free inspection

🧪 Educational & Experimental:

• Demonstrate achromatic correction vs. singlet chromatic aberration

• Measure MTF, spot diagrams, and interferometric wavefront

• Lens design instruction – classic N-BK7/N-SF5 doublet example