Control for sensorless optical wavefront correction

The acquisition of high resolution images is essential for the early detection of eye diseases. To acquire such high resolution images, it is necessary to correct for monochromatic aberrations introduced by the imaging system and the eye itself. Currently, adaptive optics systems are used to correct these aberrations and thereby achieve a higher resolution. Most of these adaptive optics systems make use of a Deformable Mirror (DM) for wavefront correction and a Shack Hartmann (SH) sensor for measuring the wavefront. The use of such a complex setup has some disadvantages. Firstly, a part of the light beam has to be diverted to the SH sensor, which decreases the signal-to-noise ratio and increases the chance of introducing extra aberrations. This can result in correcting aberrations, which are not present in the imaging light path or vice versa. In this thesis a novel low-cost optical system with a developed toolbox for control is presented to correct for these large lower order aberrations. The optical setup consists of a tunable liquid defocus lens for defocus correction and two rotational cylindrical lenses for astigmatism correction. The lens-based correctors are relatively cheap and the lower order correction (LOC) toolbox only needs a wavefront sensor once for calibration of the system, but after calibration the system can correct aberrations without a priori knowledge of the wavefront. The toolbox also addresses the problem of the defocus and astigmatism correction being dependent on each other.The complete system has been tested and shows promising results. The performance of thesystem has been compared with a not yet released defocus and astigmatism corrector developed by Varioptic with the same correction range, but the system presented here outperforms that system significantly.Embedded SystemsDelft Center for Systems and ControlMechanical, Maritime and Materials Engineerin