Bi-Convex Spherical Lenses

He Rui optics' bi-convex lenses are popular for many finite imaging applications. Bi-convex lenses are most suitable where the object and image are on opposite sides of the lens and the ratio of the image and object distances (conjugate ratio) is between 0.2 and 5. 

Bi-Convex (Double-Convex) lenses have the same radius of curvature on both sides of the lens and function similarly to plano-convex lenses by focusing parallel rays of light to a single point. As a guideline, bi-convex lenses perform with minimum aberration at conjugate ratios between 5:1 and 1:5. (Outside this range, plano-convex lenses are usually more suitable.) Bi-Convex lenses are the best choice when the object and image are at equal or near equal distance from the lens. Not only is spherical aberration minimized, but coma, distortion and chromatic aberration are identically canceled due to the symmetry. N-BK7 lenses are a great choice for most general purpose visible and NIR applications, featuring high homogeneity and low bubble and inclusion content. UV Fused Silica lenses are ideal for UV or higher energy applications, combining a very low thermal expansion coefficient and excellent transmittance down to 195 nm.