Achromatic, semi-plan, plan achromats, phase...what do they all mean? Achromatic, semi-plan, plan achromats and phase are all types of objectives. Since they can be confusing and a tad daunting when you're feeling your way through the microscope world for the first time, here's some explanations to help you understand their differences.
Achromatic Objectives: Lenses that bring parts of the color spectrum into the same plane of focus. Achromats are standard on any quality microscope. They may be designated as flatfield objectives, but typically deliver between 60-70 percent flatfield.
Semi-Plan Objectives: Objectives that are corrected to attain a flatness of field around 80-85 percent.
Plan Achromats: Objective lenses delivering nearly 100 percent flat field.
Phase: Objectives create the effect of "staining" by changing the optical light path without actually staining the slide. The benefit is that the specimen remains viable and intact.