Real optical systems are often suffering from false light caused by ghosts. In particular single reflections are critical in applications like reflected light illumination microscopy or confocal systems. The degradations of performance can be bright spots in the image or contrast, signal to noise or dynamic range reduction. Thus in these systems the suppression of first order reflections is important. State of the art optical design software supports ray trace based ghost image analysis. The automatic generation of reflex light paths is provided, but for systems with a large number of surfaces the analysis of all ghost light paths is time-consuming. Conventional Monte Carlo based non sequential ray trace sums up the reflections of all surfaces simultaneously. To achieve high accuracy a huge number of rays is necessary, what results in long computational time, especially if the distinction of surface influences needs multiple calculations. In this paper a fast method is proposed for the ranking of ghosts. It was developed for single reflections in centered optical systems. For each surface the ghost light path is calculated with paraxial and real ray trace. The ghost diameter and the corresponding illumination NA are calculated. Usually the distance of the reflex focus to the image is used as criterion to access the importance of a ghost. Here we use the power of the ghost ray bundle. It is compared with the signal strength and listed for all surfaces generating a ghost. So in one step a surface contribution of reflex powers as well as an estimation of total flux of reflected light is obtained. Due to the fact, that only a few rays have to be calculated, the method is rather fast. The accuracy can be estimated by comparison of paraxial and marginal ray trace. In the proposed method, some assumptions and approximations are made. They are assessed in respect to some practical examples, and by comparison with full brute force non-sequential ray trace. The usefulness of the fast tool is evaluated.
The measurement of aberrations is essential to qualify and improve optical system performance. Interferometry and Shack-Hartmann test are well known methods, which usually characterize only a component of the system. In addition the field dependence of aberrations is difficult to determine with these methods.
We evaluated the iterative approach based on Gerchberg Saxton Algorithm and optimized its accuracy for experimental data. The aberrations are determined from image stacks formed by a point source with varying focus position. In addition to calculating the aberrations also apodisation can be taken into account.
The numerical accuracy of the technique is up to 1/100 of a wavelength (Fringe Zernike coefficients) for ideal noiseless detection. For experimental data the main uncertainty is caused by model assumptions as the precise numerical aperture, deconvolution for finite pinhole sizes, magnification or step size in defocus as well as accuracy of equipment.
The dismatch between retrieval and direct wavefront measurement is less than 1/20 of a wavelength. Additionally the influence of different components of the optical system may be separated by measurements with exchanged components. The adjustment of an objective lens was tracked with respect to the movement of the lens elements.