Rifle Scope

Aspherical Lens

Lens is a special transparent material designed in such way that it bends parallel rays of light. In terms of its shape, a lens can be a segment of cone, plane or sphere. The idea behind the lens design is to bend rays of light in order to cross them and form and image, which can be larger or smaller than the actual object under observation. This whole process of light bending is called refraction, an according to historians, the early Greeks were the first to introduce this concept.

Aspherical lenses have curved surfaces with continuously varying degrees of curvature across the diameter of the lens. Aspherical lenses are small, compact, lighter and generally better than other lenses with spherical shape. Aspherical lenses have complex curved surface. For example, the radius of curvature can chance depending on the distance from the optical axis. The downside of spherical lenses is that they can't focus all the light beams into one point, however, aspherical lenses have better aberration correction performance, because of which, they produce an image with higher resolution and are even more compact and consist of smaller number of optical elements.

Nikon's hybrid aspherical lenses are a combination of glass and plastic. During the production process, UV-curable resin is injected between the spherical glass and the aspherical metal mold, and irradiated with UV to form a glass-resin hybrid aspherical lens.

The idea behind aspherical lenses is to eliminate optical aberrations and distortions, but keeping the lens's size and weight low at the same time. The surface of spherical lenses looks as if they were a part of a sphere, but as oppose to that, aspherical lens surfaces have a different degree of curvature at the center and the edges. The production process for manufacturing aspherical lenses is more complicated and requires ultra-high precision and a complex and expensive holographic measurement process for surface accuracy verification.

Aberration is defined as the inability to focus all light rays from a point source onto a point on film, hence aberration directly influences the resolution. The further away a light ray is from the optical center, the more pronounced this aberration becomes, making it a crucial issue for fast lenses with their larger diameter elements. Additional optical elements are needed to correct the aberration. Radical aspherical lenses are lenses that have extreme curvature.

Canon is one of the best manufactures of aspherical lenses, because Canon has special technologies employed in the manufacture of aspherical lenses and diffractive-optical elements include mold-making technology, considered to be the most difficult technology used in lens production. Their plastic molding method is based on numerous innovations that ensure precise and stable molding that involve pouring plastic into a finely crafted mold to create a lens. The other manufacturing methods are the photo-replication method and the glass molding method, more on which you can find at http://www.canon.com/technology/canon_tech/explanation/aspherical.html.