A good mirror still sees through turbulence

Changing atmospheric conditions disturb incoming wavefronts, causing twinkling and blurred detail. A well-shaped main mirror can therefore fall short of its ideal resolution.

Active optics maintains the required mirror figure; adaptive optics responds to faster wavefront disturbances. They can work together on one telescope without being the same control task.

References: [1] [2]

Reference light and deformable mirrors

The system estimates wavefront distortion from reference light and drives a deformable mirror accordingly. This optical correction during observation differs from enlarging an already blurred image.

Suitable bright natural reference stars are not available everywhere. Laser guide stars create atmospheric reference signals and expand observational access; they do not increase the intrinsic brightness of the target.

References: [1]

Correction has a domain

Reference direction, wavelength and corrected field affect performance. ESO describes multiple guide stars and wider fields as development goals, showing why a correction near one target is not an identical improvement across every field.

Wavefront correction does not remove every atmospheric absorption band or supply unlimited collecting area. Aperture, detectors, background and the target still determine what an observation can achieve.

References: [1] [3]