Product Description
Premium High-Quality Uncoated 3″ (76mm) Diameter N-BK7 Plano-Convex Lens – Long Focal Length, Excellent Condition
A professional-grade, large-aperture plano-convex lens crafted from genuine Schott N-BK7 optical glass. With a 76mm clear aperture and a long nominal focal length of 900–1000mm, this lens delivers low-aberration performance ideal for beam expansion, collimation, telescope objectives, and educational demonstrations. Uncoated surfaces offer cost-effective visible-light transmission with the flexibility to apply custom AR coatings if desired.
🔍 Key Specifications:
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Diameter: 3″ (76mm) clear aperture
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Focal Length: ~900–1000mm (f/12–f/13 focal ratio)
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Edge Thickness: 3mm (thin, lightweight profile)
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Sagitta: ~1.6mm (gentle curvature)
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Material: Genuine Schott N-BK7 borosilicate crown glass
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Design: Plano-convex – one flat surface, one gently curved convex surface
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Coating: Uncoated (~4% reflection loss per surface)
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Edge Finish: Precision-ground, ready for mounting
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Condition: Excellent – Used/Surplus, clean surfaces
✅ Condition & Notes:
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Condition: Excellent – no scratches, chips, or haze
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Origin: Surplus from professional laboratory or industrial optical stock
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Optical Quality: Surfaces are clean and polish is intact; glass is homogeneous with no bubbles or striae
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Mounting: Fits standard 3″ (76mm) lens cells and holders
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Includes: Lens only – no mounting cell or hardware
⚙️ Why This Lens is Exceptional:
🔬 Genuine Schott N-BK7:
Not generic crown glass—this is authentic Schott N-BK7, the industry standard for precision optical components. Delivers:
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Excellent transmission from 400–700nm (>90% uncoated)
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Superior homogeneity – no striae, minimal bubbles
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Stable, predictable performance across temperature ranges
📏 Long Focal Length Advantage:
The 900–1000mm focal length provides:
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Low angular magnification – ideal for beam expansion
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Reduced spherical aberration vs. short-focus singlets
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Comfortable working distance for optical bench setups
💡 Uncoated Flexibility:
Uncoated surfaces offer 4% natural reflectivity – perfect for:
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Cost-sensitive applications where 90% transmission is sufficient
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Custom coating – apply your own AR for specific wavelengths
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Polarization experiments – no coating-induced birefringence
🪶 Lightweight Profile:
At only 3mm edge thickness, this lens is surprisingly lightweight and easy to mount – no heavy glass block to support.
🛠️ Applications & Uses:
💫 Beam Collimation & Expansion:
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Collimate divergent sources (laser diodes, LEDs, fiber outputs)
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Beam expander output lens in Galilean or Keplerian configurations
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Long working distance alignment and targeting systems
🔭 DIY Telescopes & Optics:
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Objective lens for low-power, wide-field refractor telescopes
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Galilean beam expander ocular component
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Finder scope or spotting scope objective
🔬 Laboratory & Educational:
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Demonstrate lensmaker’s formula and focal length measurement
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Relay lens in optical relay systems
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Field lens in multi-element optical trains
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Physics classroom demonstrations of refraction and focusing
📷 Imaging & Projection:
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Large-format magnifier for inspection or viewing
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Projection lens in custom enlargers or solar projectors
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Schlieren imaging optics component
🎯 Laser & Light Experiments:
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Visible laser beam control (HeNe, 532nm, 635nm)
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Light collection for sensors or photodiodes
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Prototype optical systems for R&D



