Abbreviation: AS = "Aspherical Optics" (Tokina)

The abbreviation AS means "Aspherical Optics" and is seen on Tokina products.

Explanation from Tokina

A standard lens is made up of a combination of spherical lens elements. Individual “lenses” within the lens are commonly referred to as “elements”. A spherical element has an even curve to the surface of the glass. However, there can be problems with such elements; light entering the center of the lens and light entering at the edge may not be perfectly focused at the same point. This is called spherical aberration. More advanced computer assisted optical designs are creating lenses with more spherical elements. More spherical elements within a lens means a greater risk of spherical aberration having a negative impact on optical quality.

Wide-angle zoom lenses and wide-angle lenses with large apertures are especially at risk for spherical aberration.

To eliminate spherical aberration, Tokina employs aspherical all-glass elements in many of its optical designs to correct this problem. The aspherical shaped surface of the lens element focuses light rays entering both th

See examples of effected products

	Tokina AT-X 16-28mm F2.8 PRO FX
	Tokina AT-X Pro 16-50mm F2.8 DX

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