What Is an APO Lens?
A lens focuses light by bending it. Each color of light bends by different amounts, creating a soft focus and a color fringe around objects. This color fringe is called chromatic aberration. Apochromatic (APO) lenses, are designed to reduce chromatic aberration.
The Speed of Light
When light travels from air through a lens, it slows down. This change of speed bends (or refracts) the light. Each color of light is refracted by a different amount, causing the various colors of light to focus at separate places. This is how a glass prism creates a spectrum.
Types of Glass
Glass can be made from ground flint, a mixture of soda and lime (crown glass), silica, dolomite, and other materials. Flint glass and crown glass are commonly used in optics. Fluorite and other extra-low dispersion materials are used in better quality lenses.
Simple Lenses
A simple lens, such as an eyeglass lens, is one piece of glass that is curved in order to bend light. Simple lenses may be convex or concave.
Chromatic Aberration
Simple lenses will focus the different colors of light at different spots, which creates an overall soft focus and color fringing that is most evident around high contract objects, such as the edge of a building against the sky. Chromatic aberration is undesirable.
Apochromatic Lenses
An apochromatic lens uses three pieces of glass to focus the three primary colors of light (red, green and blue) into focus at the same spot, which reduces or eliminates chromatic aberration and sharpens the image.
Uses of APO Lenses
Apochromatic lenses are widely used in photography, microscopy, and astronomy. They tend to be expensive because they contain more glass, and often the glass is of very high-quality or exotic materials.
Tags: colors light, Apochromatic lenses, chromatic aberration, color fringe, color light, crown glass, Each color