Customer Background & Challenge

The customer develops IP67 outdoor PTZ surveillance cameras for highway and perimeter security. Their original polycarbonate dome suffered from light reflection and gradual scratch marks after long-term outdoor exposure. They required a hemispherical optical cover that meets these requirements:

• High visible transmission, low reflection to avoid glare and ghosting for 4K imaging
• Stable optical performance under -30°C ~ +60°C outdoor temperature cycles
• Controlled surface quality: 60/40 scratch/dig, tight concentricity tolerance
• Cost-effective, not over-specified with expensive sapphire for non-deep-sea applications
• Multi-layer AR coating for 400–700 nm visible band

After material evaluation, our optical engineering team recommended N-BK7 crown glass rather than sapphire or fused silica. Review N-BK7 Optical Glass Material Introduction for full material property data.

Custom Specifications

• Material: N-BK7 optical glass
• Geometry: Hemispherical dome, outer diameter 92 mm, wall thickness 4.0 mm
• Optical coating: Broadband AR coating @400–700 nm, average transmittance ≥98%
• Surface quality: 60/40 scratch / dig
• Tolerance: Concentricity ≤0.03 mm, edge chamfer for assembly sealing
• Quantity: Paid prototype batch first, followed by serial production of 220 pcs

Engineering & Fabrication Process

We first reviewed the customer’s mechanical drawing and camera optical path simulation to confirm the dome curvature and coating spectrum. The workflow included blank cutting, curve grinding, fine polishing, cleaning, AR coating and final interferometer inspection.

We clearly communicated the material limits to the customer: N-BK7 is suitable for outdoor surveillance, but it is not designed for deep-sea high-pressure or heavy saltwater immersion without additional protective treatment. For subsea high-pressure camera housings, sapphire domes are the preferred option.

Final Test Result & Outcome

• AR coating performance verified by spectrophotometer, average transmission hit 98.2% across visible band
• No image distortion, ghosting or flare issues in the customer’s camera imaging test
• Passed thermal cycling test from -30°C to +60°C, no coating peeling or optical shift
• Prototype approved, mass production delivered on schedule; customer placed repeat orders in the next quarter

Key Takeaway for Optical Design

N-BK7 is a mature, cost-efficient crown glass for visible-band camera dome covers. It is an ideal choice for outdoor surveillance, machine vision and general visible optics, while sapphire or fused silica should be selected for high-pressure, deep UV or extreme abrasion scenarios.