Double convex lenses have two outward curved surfaces, a positive focal length and are useful for 1:1 imaging and in multi-element systems. N-BK7 bi-convex lenses are used for focusing and the lenses are best choice when the object and image are at equal or near equal distance from the lens. The two surfaces of the bi-convex lenses are finely polished.
Double convex spherical aberration is larger than that of the plano-convex lens, so focal spot may not gather at one point.
Custom Made specifications:
| Material | N-BK7 or H-K9L |
| Diameter range | 2mm to 500mm |
| Tolerance | +/-0.05mm |
| Thickness tolerance | +/-0.05mm |
| Surface quality | 40-20 or better |
| Surface flatness | Lambda/4 or better |
| Centering | 1 arc min |
| Bevel | 0.1-0.3mm |
| Coating | AR coated for different wavelengths R<0.5% |
