Rectangular Array
The RA algorithm traces a grid of rays through the pupil. The advantage to the RA algorithm is the ability to accurately account for the effects of vignetting in the merit function. This is useful in systems such as obscured telescopes and camera lenses which intentionally clip troublesome rays. The disadvantage to the RA algorithm is speed and accuracy. Usually, more rays are required to achieve a given degree of accuracy than the GQ algorithm. The bottom line: don't use RA unless you are using surface apertures.
The RA algorithm requires specification of the "Grid" size, and the "Delete Vignetted" option.
Grid Determines the number of rays to be used. The grid size can be 4x4 (16 rays per field per wavelength), 6x6 (36 rays per field per wavelength) etc. Rays on the grid are automatically omitted if they fall outside the entrance pupil, so the actual number of rays used will be lower than the grid size squared. Selecting a larger grid size generally yields more accurate results at the expense of slower execution. However, there may be an advantage in choosing a large grid density, and then selecting the "Delete Vignetted" checkbox (described in the next paragraph). The reason is that a large grid density will fill the pupil with rays, and then the operands which are vignetted will be deleted. The result is a reasonable number of rays which accurately reflect the aperture of the system.
Delete Vignetted If selected, each ray in the merit function will be traced through the system, but if it is vignetted by a surface aperture, if it misses any surface, or if it is total internal reflected at any surface, then the ray is deleted from the merit function. This keeps the total number of rays in the merit function to a minimum. The disadvantage is that if the vignetting changes as the design is optimized, then the merit function may have to be regenerated. It is always a better choice to use the vignetting factors and then use the GQ algorithm than to delete vignetted rays if possible. Vignetting factors can be adjusted, if required, during optimization using SVIG in the merit function.
Note that OpticStudio will attempt to trace any ray defined in the merit function regardless if that ray is vignetted or not. For example, if the chief ray height is targeted using REAY, and there is a central obscuration that vignettes the chief ray, OpticStudio will still trace the ray and use the operand results as long as the ray can be traced. OpticStudio does not check to see if defined rays are vignetted, because this introduces substantial overhead during optimization.
In general, avoid vignetting of rays by surface apertures, and use vignetting factors to shape the beam size when possible. To optimize on the fraction of unvignetted rays, a macro must be defined to perform the required computations. However, this method is very prone to stagnation during optimization because small changes in lens parameters lead to discrete changes in the merit function as rays abruptly jump from being vignetted to not being vignetted.
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