Plan" designates that these objectives produce a flat image across the field of view. "Achromat" refers to the correction for chromatic aberration featured in the lens design. These objectives have chromatic correction for three wavelengths, and feature spherical correction at two wavelengths. Plan achromats produce their best images for green light. In white light, the plan achromats give satisfactory images for color photomicrography, but the results are not as good as objectives that feature better correction, such as plan fluorite objectives (see below).