Figure 1
From: Adaptive optical microscopy: the ongoing quest for a perfect image

Principle of aberration correction in high resolution optical microscopes. (a) Aberrations are induced as light passes through the specimen due to variations in refractive index, leading to a distortion of the focus. (b) The deformable mirror introduces an aberration that cancels out the specimen induced aberration, restoring a diffraction limited focus. (c) The deformable mirror also corrects for aberrations induced in the detection or imaging path.