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.
🔍 Key Specifications:
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Diameter: 50 mm (precisely ~50.8 mm standard)
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Effective Focal Length (EFL): 800 mm (f/16 focal ratio)
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Design: Biconvex cemented achromatic doublet
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Edge Thickness: ~7.5 mm total
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Glass Types: N-BK7 (crown, positive element) + N-SF5 (flint, negative element)
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Coating: Broadband VIS AR coating – <0.5% reflectivity, >98% transmission per surface (400–700 nm)
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Orientation Mark: Arrow etched on edge – points toward more strongly curved (higher power) surface
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Condition: Pristine – no scratches, chips, or delamination
✅ Condition & Notes:
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Condition: Excellent – Like New / NOS Quality
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Optical Surfaces: Absolutely clean – no coating defects, haze, or cleaning marks
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Cement: Perfect edge bond – no separation, yellowing, or stress birefringence
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Markings: Professional edge arrow for correct orientation
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Includes: Lens only – no mounting cell or hardware
⚙️ Optical Design Excellence:
🔬 Premium Glass Pairing: N-BK7 + N-SF5
This classic achromatic combination offers:
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Superior chromatic correction – brings red and blue to common focus
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Reduced spherical aberration – f/16 design is exceptionally forgiving
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Excellent transmission from 400–700 nm
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Thermally stable – minimal focus shift with temperature
📏 Long Focal Length Advantage:
The 800 mm EFL at f/16 provides:
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Diffraction-limited on-axis performance – aberration-free even at full aperture
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Forgiving tolerances – ideal for first-time telescope makers
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Comfortable eye relief in visual astronomy applications
💎 Broadband AR Coating:
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<0.5% reflectivity across 400–700 nm
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>98% transmission per surface – maximizes throughput
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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.
🛠️ Applications & Uses:
🔭 Telescope Objective – Planetary & Lunar Excellence:
The 50mm f/16 achromat is a classic refractor objective configuration:
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Minimal chromatic aberration – false color virtually invisible
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Sharp, high-contrast views of the Moon, Jupiter, Saturn, and double stars
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Wide-field capability with low-power eyepieces
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Perfect starter scope for amateur telescope makers (ATM)
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Ideal solar projection (with proper filtration) – safe, detailed white-light views
💫 Beam Collimation & Expansion:
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Collimate divergent sources (laser diodes, LEDs, fiber outputs) over long working distances
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Beam expander output lens – low divergence, minimal wavefront error
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Alignment telescope objective – precision autocollimation setups
🔬 Imaging & Relay Optics:
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Low-distortion focusing for machine vision systems
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Relay lens in microscopy extensions or periscopic viewers
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Tube lens for infinity-corrected microscope objectives
📷 Projection & Magnification:
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Slide or enlarger lens – color-critical reproduction
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Solar projection – detailed white-light Sun viewing
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Large-format magnifier – distortion-free inspection
🧪 Educational & Experimental:
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Demonstrate achromatic correction vs. singlet chromatic aberration
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Measure MTF, spot diagrams, and interferometric wavefront
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Lens design instruction – classic N-BK7/N-SF5 doublet example



