A Convex Spherical Mirror is a mirror which curves inward away from the incident light. Shanghai Optics produces high quality convex spherical mirrors with a variety of diameters and focal lengths. These precision mirrors are ideal for imaging applications, specifically, for increasing an imaging systems field of view.

Understanding the Convex Spherical Mirror

The geometry of a convex mirror is that of a portion of the sphere. Both incident light and the viewer are outside of the sphere.  Imagine extending the sphere and finding its center. This is defined to be the center of curvature.  The line between the real image and the center of curvature is called the optical axis. The focal point of the mirror will be between the mirror and the center of curvature, and the image will appear to be between the focal point and mirror. We call this image virtual because the rays are not actually transmitted to the other side of the mirror; they are simply reflected at an angle from the outer curve.  The image will always be reduced in size, and it will always be upright.

If a spherical mirror is small, as compared to the radius of curvature, it may be considered a good approximation of an ideal parabolic mirror and will exhibit little spherical aberration. Parallel rays strike the front of the mirror and are reflected back, and each ray may be interpolated to cross at a single point (the virtual focus).  Mirrors with shorter focal length will not produce as clear images. They will, however, have a wider field of view.

Coating and Substrate

Convex Spherical Mirrors are manufactured from high quality BK7 Grade A optical glass, Corning Fused Silica 7980, JGS1, JGS2. BK7, Schott borosilicate-crown glass, has a high refractive index homogeneity and uniform transmission in the visible. Corning Fused Silica 7980, a noncrystalline silicon dioxide produced through flame hydrolysis, has a very low thermal expansion coefficient and exceptionally good ultraviolet transmittance. JGS1 is high quality ultraviolet grade fused silica, and features high purity, a low thermal expansion coefficient, and excellent transmission in the ultraviolet range.

Our curved mirrors are coated with high quality metallic coating on the outer surface of the sphere. We offer both enhanced aluminum and protected gold coatings. For applications in the visible spectrum we recommend enhanced aluminum for a reflecting surface, but protected gold will provide a better reflection for NIR, MWIR, and LWIR spectra.

Convex Spherical Mirror Factory Standards

At Shanghai Optics we use state of the art metrology equipment to ensure every lens, mirror and optical component to leave our factory meets all applicable standards and specifications. Our factory standard convex spherical mirrors feature a surface flatness of λ/4. Our standard diameter tolerance is +0, -0.1mm, and the clear aperture guaranteed to be 90% of the diameter.  The surface quality is 40-20 scratch dig.

Please contact us to discuss manufacturing limit or custom specifications. We manufacture a wide range of concave and convex mirrors and our design specialists will be happy to work with you determine what the best optics are for your situation.

Factory Standards

• Surface flatness: λ/4
• Surface quality: 40-20
• Diameter: +0, -0.1mm
• Clear aperture: >90% diameter