Image Triangulation
Optical metrology systems utilize specialized algorithms and hardware adjustments to correct for parasitic movements of a specimen along the viewing axis. In surface profiling and strain analysis, out of plane displacement compensation isolates true in plane deformation from apparent strains caused by the specimen moving closer to or further from the camera. This correction is critical for maintaining high accuracy in digital image correlation and interferometry.
Telecentric Correction
Dual camera stereoscopic systems naturally resolve this issue by using geometric triangulation to measure three dimensional displacement vectors. If only a single camera is available, compensation can be achieved by using telecentric lenses that maintain constant magnification regardless of the distance to the specimen. Alternatively, a displacement sensor can monitor the axial position and trigger a translation stage to restore the focal distance.
Fiducial Tracking
Computational algorithms can also estimate the magnification changes by tracking known fiducial markers outside the deformation zone. By applying scaling corrections to the captured images, the algorithm removes the fictitious strain component. This approach reduces the need for expensive optomechanical hardware.
Vibration Noise
Even with compensation, high frequency vibrations along the optical axis can introduce residual noise that limits the displacement resolution. Minimizing these vibrations requires pneumatic isolation tables and rigid mounting fixtures.
