superachromats

A superachromat is an optical design intended to correct chromatic aberration beyond that achieved by conventional achromatic lenses. By combining three or more glasses with carefully chosen dispersion properties, and sometimes incorporating aspheric elements, a superachromat aims to bring multiple wavelengths to the same focal plane with much lower residual color across a broad spectral range.

Design and principles: Traditional achromats use two glasses to align two wavelengths, reducing axial color but leaving significant residual chromatic error, especially outside the visible extremes. Superachromats extend this approach by using additional glass types and optical elements to suppress both primary and secondary chromatic aberrations over a wider band. Practical implementations often employ low-dispersion or exotic glasses (such as extra-low dispersion, fluorite, or other specialized materials) and may include multi-element cemented groups or air-spaced configurations, along with optimized surface profiles and coatings to improve contrast and transmission.

Applications: Superachromats appear in high-performance photographic lenses, certain telescope objectives, and scientific instrumentation where accurate color rendition and sharp contrast across a broad spectrum are critical. They can be found in professional telephoto designs and precision eyepieces intended for demanding imaging or observation tasks.

Limitations and context: The approach increases design and manufacturing complexity, cost, and potential sensitivity to alignment and wavelength range. In practice, performance is bounded by material availability, optical tolerances, and the specific spectral band of interest. Superachromats are related to, but distinct from, apochromats, which target even broader correction across multiple wavelengths, including the secondary spectrum.