Low-dispersion glass

In other words, the light passing through the glass has a smaller spread or dispersion between its constituent colors, resulting in a reduced "rainbow effect" at high-contrast edges.

Lens materials to the left of those have a higher Abbe number for a given refractive index, and may be considered to be low-dispersion types, including many of the lanthanum-doped glasses.

The shallow depth of field provided by a telephoto lens also allows the subject of the photography to stand out better against the background.

The low chromatic aberration of SLD glass allows the lens to always stay in focus, from visible light to infrared.

It is used in binocular objective lenses to help focus the light waves of the color spectrum on the human eye, and to deliver bright, sharp images.

[15] Thoriated glass is doped with thorium dioxide, resulting in a lens material with high refractive index and low dispersion, suitable for apochromatic designs.

[18] However, additional elements had to be added to preserve the amorphous structure of the glass and prevent crystallization which would cause striae defects in images captured through those lenses.

These so-called "borate flint" glasses, which Schott classifies as KzF (kurzflint), are however highly susceptible to corrosion by acids, alkalis, and weather factors.

In addition, fluorite has poor shape retention and is very fragile, requiring special handling to process into lens elements.