Precision 70mm Fused Quartz Hyperbolic Convex Secondary Mirror

Premium 70mm diameter hyperbolic convex front-surface mirror on a premium low-expansion fused quartz (fused silica) substrate. This is a high precision, laboratory-certified optic originally from a leading U.S. defense and research facility known for advanced optical systems including astronomical applications where thermal focus shift must be minimized.

Key Specifications:

• Level 1 Certified (high-level inspection/quality assurance)

• Diameter: 70 mm

• Edge Thickness: 10 mm

• Center Thickness: ~12.5 mm

• Sagitta (convex rise): ~2.5 mm

• Base Radius of Curvature: ~246 mm (spherical base for the hyperbolic profile)

• Effective Focal Length: ~-123 mm (convex diverging mirror)

• Substrate Material: Fused quartz – extremely low thermal expansion, high purity, excellent polishability, and superior stability across temperature changes

• Front Surface Coating: Protected aluminum (broadband high reflectivity ~90-95% visible, neutral color, durable dielectric overcoat for longevity)

• Back Surface: Flat, uncoated bare quartz

• Edge Finish: Fine ground with precision beveled chamfers on both faces

• Features: Two small gold-colored fiducial marks on the edge for optical axis alignment and collimation

Condition: Excellent – bright, uniform coating with no scratches, haze, pitting, or defects visible. Reflections are crisp and neutral. Appears very lightly used or unused.

Primary Applications:

• Telescope Secondary Mirror: Designed as a hyperbolic convex secondary for Cassegrain, Ritchey-Chrétien, or similar high performance reflecting telescope systems (suits ~8–12 inch primary apertures in compact, high-magnification designs with excellent aberration correction)

• Precision beam folding/divergence in laser systems, interferometers, optical testing, or scientific instruments

• Any setup requiring a thermally stable, high-performance convex mirror (fused quartz outperforms standard glasses like BK7 or Pyrex) with Defense lab certification make this far superior to commercial off-the-shelf mirrors)

This is a high-end Defense Lab surplus optic_the kind of premium optic used in advanced research, aerospace, or observatory-grade systems. The Level 1 certification and serial tracking underscore its quality and traceability.

Highly desirable for serious amateur astronomers, custom telescope builders, universities, research labs, or collectors of high-end surplus optics.