OptoSigma 2 inch achromatic doublet lens 500mm focal length

Product Description

OptoSigma 2″ (50.8mm) Achromatic Doublet Lens – 500mm FL, VIS Coated – Excellent Condition

A high-quality cemented achromatic doublet lens from OptoSigma, optimized for the visible spectrum (400–700 nm) with broadband multi-layer anti-reflection coating. With a 50.8mm (2-inch) diameter and 500.3mm effective focal length (f/10) , this diffraction-limited optic delivers superior chromatic aberration correction and high-contrast imaging—ideal for telescope objectives, beam collimation, and precision optical systems.

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🔍 Key Specifications:

📐 Dimensions & Optical Design:

• Manufacturer: OptoSigma (formerly Sigma Koki)

• Part Number: 026-1720 (legacy) | Equivalent to: DLB-50.8-500PM (current)

• Diameter: 50.8 mm (2 inches) – standard mounting compatibility

• Effective Focal Length (EFL): 500.3 mm (f/10 focal ratio)

• Design: Cemented achromatic doublet – crown + flint glass

• Clear Aperture: ~45 mm (excellent edge-to-edge performance)

• Coating: Broadband multi-layer AR for visible spectrum (400–700 nm)

• Transmission: >99% per surface (typical), <0.5% reflectivity

💎 Substrate & Surface:

• Glass Types: Precision crown/flint pairing – superior color correction

• Surface Quality: Diffraction-limited – excellent figure, no visible defects

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

✅ Condition:

• Optical Surfaces: Excellent – pristine, no scratches, chips, or coating damage

• Edges: Clean, precision-ground, ready for standard 50mm lens cells

• Origin: Professional optical laboratory surplus – carefully handled and stored

• Includes: Lens only – no mounting cell or hardware

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⚙️ Why This Achromatic Doublet is Exceptional:

🔬 Diffraction-Limited Performance:
At f/10, this doublet operates in the diffraction-limited regime—aberration-free across the entire visible spectrum. This is not a compromise optic; it is a precision instrument capable of resolving to the theoretical limits of its aperture.

🎯 Optimized f/10 Focal Ratio:
The deliberate “slow” f/10 design offers:

• Minimal spherical aberration – sharp, high-contrast images

• Forgiving alignment tolerances – ideal for first-time telescope makers

• Excellent off-axis performance – no field curvature concerns

• Comfortable eye relief with standard eyepieces

💎 Premium OptoSigma Pedigree:
OptoSigma (formerly Sigma Koki) is a respected Japanese optical manufacturer known for:

• Rigorous quality control – each lens individually tested

• Superior glass selection – premium crown/flint pairs

• Precision cementing – permanent, thermally stable bonds

• Durable AR coatings – resistant to cleaning and environmental exposure

📏 500mm Focal Length – The “Sweet Spot” for 2″ Achromats:

• Long enough for serious planetary/lunar observing (100x+ with common eyepieces)

• Short enough for manageable tube length (~20″ telescope)

• Slow enough for diffraction-limited performance

• Fast enough for bright, engaging wide-field views

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🛠️ Applications & Uses:

🔭 Telescope Objective – Planetary & Lunar Excellence:
The 50mm f/10 achromat is a classic refractor configuration beloved by amateur astronomers:

• Crisp, high-contrast views of the Moon – see detail down to 1-2 arcseconds

• Sharp planetary images – Jupiter’s cloud belts, Saturn’s ring division, Mars polar caps

• Double star resolution – split close pairs to Dawes limit (~2.3 arcseconds)

• Wide-field capability – sweeping star fields with low-power eyepieces (2°+ FOV)

• Ideal first telescope – forgiving, portable, instantly usable

💫 Beam Collimation & Expansion:

• Collimate divergent sources (laser diodes, SLEDs, fiber outputs) with diffraction-limited wavefronts

• Beam expander output lens – clean, low-divergence beams

• Spatial filter output collimator – preserve Gaussian profiles

• Alignment telescope objective – precision autocollimation

🔬 Imaging & Relay Systems:

• Relay lens in microscopy extensions and periscopic viewers

• Focusing element in spectrometers and monochromators

• Tube lens for infinity-corrected microscope objectives

• Machine vision – high-resolution inspection optics

🧪 Laboratory & Experimental:

• Optical bench experiments – measure MTF, spot diagrams, interferometric wavefront

• Lens design instruction – classic achromat example

• Prototype optical systems – proven, predictable performance

📷 Projection & DIY:

• Enlarger lens – color-critical print making

• Solar projection (with proper filtration) – safe, detailed white-light Sun viewing

• Custom telescope projects – build your own “classic 2-inch refractor”