from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A lens that imparts little color; a lens that is achromatic.
from The Century Dictionary and Cyclopedia
- n. In optics, a lens or system of lenses corrected for chromatic aberration.
PS: Vision in a complete achromat: a personal account is a very interesting feature on achromatopsia by vision scientist Knut Nordby.
The magician's tale / David Hunt —An achromat suffering from total color blindness, Kay possesses a vision that informs her world and sharpens her skills as talented photographer.
An achromat brings those two wavelengths to the same focus, with other wavelengths very slightly out of focus.
You can, for example, buy semi-plan apochromatic objectives and plan achromat objectives.
An apochromat is corrected for three specific wavelengths of light -- usually red, green, and blue -- and brings those three wavelengths to the same focus, providing slightly sharper images than an achromat.
The first section on the knowledge argument has a number of special treats: Knut Nordby, the achromat color scientist, with a piece on what it's like to be in Mary's situation;