11. For complements of trees, the achromatic number can be computed in polynomial time. 12. Had he done so, he would almost certainly have invented the achromatic lens. 13. Colors nearest the center or the poles are most " achromatic ". 14. He suggested using two achromatic lenses of " six inches focus " placed apart. 15. White in pigment or dye form has no color ( it is called achromatic ). 16. This was especially true in refracting telescopes, before the invention of achromatic objective lenses. 17. Its bill is also achromatic , but tan near the bottom of the lower jaw. 18. :: There is a rare form of colourblindness where the vision becomes completely achromatic . 19. The 1955 model came with a meniscus lens, later replaced with an achromatic lens. 20. For example, microlensing is achromatic .
