Abstract
Purpose :
The Visual Strehl ratio based on the optical transfer function (VSOTF) is one of the best metric of visual performance that can be calculated from wavefront aberrations. The goal is a theoretical analysis of the impact of longitudinal vibrations on the vision quality, as studied experimentally in 1965 by Lohmann and Paris, when vibrations were considered to affect the defocus aberration component of the wavefront error. In this setting, we calculate the averaged VSOTF and discuss the effect of vibrations on this metric.
Methods :
An expression for the Visual Strehl ratio calculated in the spatial frequency domain of the optical transfer function (VSOTF) is found for the case of a time-varying dynamic optical system with circular symmetry. Furthermore, expressions for two forms of temporally averaged VSOTF were studied, suitable for efficient numerical evaluation. This lays a methodological foundation for numerical and analytic study of the effect of longitudinal vibrations that, in this work, are considered to affect specifically the defocus aberration. Finally, relation between both averaged metrics is examined.
Results :
With no vibrations, VSOTF is a monotonically decreasing function of defocus aberration (up to approximately 1.25 D). Several experiments have been carried out in order to detect a possible improvement of visual quality as a function of the amplitude of vibration, for given values of basal defocus (offset). It is shown that such a phenomenon occurs starting from approximately 0.75 or 1D of offset, depending on the averaging method for the VSOTF (either in the pupil or the image plane). Also, the computational efficiency of the semi-analytic method of this work for calculating the VSOTF metric is compared with the standard DFT approach, being approximately 30 times faster.
Conclusions :
Our numerical experiments confirm the positive effect of the longitudinal vibrations even in the simplest setup of defocus aberration. For appropriate combination of the offset and the amplitude we obtain higher values of the averaged VSOTF in comparison with those in the absence of vibrations. The proposed analytic approach is shown to be a computationally effective method of assessing image quality in comparison with the standard DFT-based methods.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.