Hi Dusan,

The built-in Grid Distortion plot (which would be used to see barrel or pincushion distortion) will always trace a perfect grid of chief rays in object space and see where the distorted chief ray falls in the image plane.  The percent distortion is then calculated based off the predicted vs the real chief ray that is traced.  In order to visualize and calculate the “combined” distortion of 2 optical systems, there are 3 approaches:

1. Physically model the combined optical system.  This would involve modeling the front part of the optical system that is initially causing the distorted square, the eyepiece, and the human eye. 
2. Create the distorted pin-cushion grid as a PNG file and use the Geometric Image Analysis to calculate how the eyepiece will distort the input grid.
3. Create a custom analysis that individually traces chief rays at different object positions which correspond to the distorted pin-cushion grid.

The first approach will automatically calculate the percent distortion but the second and third options will only visually show the new distortion; you will need to manually calculate the predicted chief ray location and then compare that to what either the GIA or the custom analysis shows for the real ray.  The Grid Distortion section of the help file goes into detail about how to calculate the predicted chief ray location.  The easiest way to calculate the percent distortion and to make sure it aligns with OpticStudio’s calculation would be to use the ABCD and DISA Merit Function Operands.  You will need to use either the ZPL or ZOS-API to loop through each object space field location.

Hi Michael

Thank you for your excellent feedback. I am repeating my reply from 2 days ago as it obviously hasn’t been sent.

Attached are pictures of the object (barrel, -8.5% distortion) lying on a concave surface towards the eyepiece (barrel distortion -7.5%) and a picture of grid distortion of the “combination”.

ZEMAX Eye Model has been used for the eye.

Geometric bitmap analysis renders the image of the object on the retina with almost the same negative distortion as that of the object.

Grid distortion however, is almost zero, which I would actually expect as a result of the fact that the object as well as the eyepiece feature almost the same negative distortion.

Question: what distortion does the eye actually see?

Thanks, Dusan