Plan Objectives vs Semi-Plan Objectives

There are typically three types of brightfield microscope objectives that you may encounter.

1. Standard Achromat Objectives
2. Semi-Plan Objectives
3. Plan Objectives

Microscope lenses are curved, resulting in an image that is slightly out of focus at the edges when using a standard achromat objective. An achromat objective guarantees that 60% of the field of view will have a quality flat focus. Semi-plan objectives guarantee a flat field for 80% of the field of view. Plan objectives guarantee 100% and are the best quality objectives.

"Achromat" actually refers to the correcting for color dispersion effects, and you may run across descriptions such as plan achromat objectives or even semi-plan achromat objectives.

Image of frog's blood captured with the Motic BA310 using plan objectives at 1000x magnificaiton. You can learn more about microscope objective lenses here.