Optical Lens Buying Guide: How to Choose the Right Lens
Optical lenses converge or diverge light and sit at the core of imaging, illumination, laser, and inspection systems. Before you order one, it helps to match the lens type, material, and precision grade to the actual application — the checklist below covers the decisions that matter most.
Key Specifications at a Glance
| Parameter | Common Options |
|---|---|
| Common substrates | N-BK7, UV fused silica |
| Diameter range | 3 mm–300 mm (5 mm–100 mm in stock) |
| Diameter tolerance | ±0.10 mm (standard), ±0.05 mm (precision) |
| Surface accuracy | λ/4 (standard), λ/10 (precision), tested at 633 nm |
| Surface quality | 60-40 scratch-dig (standard), 20-10 (precision) |
| Coating options | Uncoated, single-layer MgF2, multi-layer broadband AR |
Step 1: Match the Lens Type to the Application
- Imaging systems (cameras, microscopes): an achromatic doublet lens keeps chromatic aberration under control
- Laser focusing and collimation: a plano-convex or biconvex spherical lens is simple and cost-effective
- Aberration correction: a meniscus lens helps flatten the field without adding much optical power
- Line focusing or beam shaping: a cylindrical lens
Step 2: Choose a Substrate
N-BK7 optical glass is the workhorse substrate for visible-light applications — good transmission, low cost, widely stocked. If your system runs into the UV range, or you need a higher laser damage threshold and lower thermal expansion, fused silica is the better fit, at a higher price.
Step 3: Pick a Precision Grade
Precision grade drives cost, so it pays to right-size it:
- General illumination or non-imaging use: standard grade (λ/4 surface accuracy, 60-40 scratch-dig) is usually enough
- Precision imaging or interferometry: go with precision grade (λ/10, 20-10)
- Laser systems: also check the laser damage threshold, and make sure the AR coating is designed for your operating wavelength
Step 4: Decide on an AR Coating
Every uncoated glass surface reflects about 4% of the incoming light. In a multi-lens system, that loss adds up fast. If throughput matters, add an anti-reflection coating — single-layer MgF2 covers most standard bands, while multi-layer broadband AR coatings suit wide-spectrum or high-precision systems.
FAQ
What's the difference between diameter and clear aperture?
Clear aperture is smaller than the nominal diameter because the lens edge is chamfered. Leave some margin when sizing a lens for your mount.
Should I buy a stock lens or order a custom one?
Check the stock size chart first — it covers most standard applications. Custom lenses only make sense for non-standard radii, unusual dimensions, or specific coating requirements.
