Spherical Singlet Lenses: Types, Specs & Applications
A spherical singlet lens has one or two surfaces ground to a constant radius of curvature — the simplest and most widely used optical lens design. Because a sphere is easier to generate, polish, and test than any other surface, spherical singlets remain the default choice for focusing, collimating, and imaging applications across the visible and near-IR range.
Key Specifications at a Glance
| Parameter | Typical Value |
|---|---|
| Substrate | N-BK7, UV fused silica |
| Diameter | 5 mm–100 mm (stock) |
| Focal length range | 10 mm–1000 mm |
| Diameter tolerance | ±0.05 mm to ±0.10 mm |
| Center thickness tolerance | ±0.05 mm to ±0.10 mm |
| Surface accuracy | λ/4–λ/10 at 633 nm |
| Centration | <3 arcmin (standard grade) |
| Coating | Uncoated / single-layer MgF2 / broadband AR (400–700 nm, 650–1050 nm, and other common bands) |
Common Spherical Lens Shapes
- Plano-convex / plano-concave — one flat surface and one curved surface; easier to manufacture and inspect, so it's usually the lower-cost option
- Biconvex / biconcave — both surfaces are curved, which lets you reach a shorter focal length for a given lens diameter
- Meniscus — one convex and one concave surface, typically paired with other lenses to correct aberration rather than used on its own
Choosing Focal Length and Diameter
Focal length sets the spot size and working distance; diameter sets the clear aperture and how much light the lens collects. As a rule of thumb, a shorter focal length converges or diverges light faster, and a larger diameter gathers more light but also makes edge aberrations more noticeable — the two need to be balanced against each other for the application.
Applications
- Laser beam collimation and focusing
- Basic imaging systems
- Fiber coupling
- Beam homogenizing and concentrating for illumination
Buying Tips
Spherical singlet lenses come in a wide range of stock sizes, so most standard applications can be filled directly from a catalog. Custom parts are typically only needed for non-standard focal lengths or diameters. When ordering in volume, confirm both the tolerance grade and the coating waveband up front — that avoids receiving lenses that don't quite match the rest of the optical system.
