Achromatic lenses are doublet systems consisting of one crown and one flint element, cemented together along a matching curvature, so that white light coming into the lens is all focused (imaged) at the same point on the other side of the lens.They are designed to minimize spherical and chromatic aberrations for infinite conjugate, visible spectrum imaging applications. When used on-axis, an achromatic lens focuses an parallel input beam to a perfect "point", limited only by the effects of diffraction. This performance can be achieved over a broadband of wavelength. Achromatic lenses can be used to collimate and focus laser beams. They can also be used for high-quality imaging on-axis. However, the off-axis performance is significantly worse than the on-axis performance. If your application requires good optical performance off-axis as well as on-axis, multi-element lenses.