Lateral color is an off-axis aberration resulting from a difference of image scale at each wavelength.
Above: Lateral color arises from a difference in image scale depending on wavelength
Lateral color causes colored fringes at the edge of the field. The stars will appear to split into red and blue halves, pointed toward the center of the field. This is most often seen in very wide-field instruments such as binoculars, although only the least expensive binoculars should show any noticeable lateral color.
Above: Severe lateral color appears as an overlapping rainbow of star images
Telescopes with Lateral Color
Most telescopes do not suffer from noticeable lateral color. Longitudinal color is much more noticeable in systems with chromatic aberration. Of course, all-reflective systems such as Newtonians do not suffer from either longitudinal or lateral color. Lateral color often arises from thick lens elements with a fair amount of optical power. For example, Schmidt-Cassegrain telescopes have thin lenses with little optical power and therefore exhibit little lateral color. Maksutov-Cassegrains, on the other hand, have thick corrector lenses with higher optical power than a Schmidt corrector. Maksutovs will typically have 200 to 300 times more lateral color than an equivalent Schmidt. However, this is still a very small and insignificant amount in most systems.