Achromatic LensesAchromat consists of a positive low-index Crown Glass lens element cemented to a negative high-index Flint Glass lens element. The elements are chosen so as to cancel chromatic aberration at two well-separated wavelengths, usually in the blue and red region of the spectrum. Focal length is constant at those two wavelengths and focal length shifts are virtually eliminated across the visible wavelengths. One frequent use is to achieve diffraction limited focusing of a laser beam. Negative Achromat is typically used when there is a need to eliminate chromatic aberration. In addition to reducing chromatic aberration at the design wavelengths, spherical aberration and coma are greatly reduced.

Specifications:
Design Wavelength: 480.0nm, 546.1nm, 643.8nm
Diameter: from 2.0mm to 90.0mm
Diameter Tolerance:+0.0, -0.10mm
Paraxial Focal Length: ±2%  at 546.1nm
Centration: 3 arc minutes
Clear Aperture: >80%
Surface Figure: lambda/4 at 632.8nm
Surface Quality: 60-40 scratch and dig
Coating: Single layer MgF2 broadband AR coating
Protective Bevel