Questions about the Grid Distortion

Question

Hello All,Supposed the definition of grid distortion is the position deviation on the image between chief ray and the centroid one for a specific field point.  Case one: In zemax, for the grid distortion, when select different reference field, why the grid distortion is different?  What is the reference field used for during the plot of grid distortion?  Case two: In fact, if there is a rectangular field grid made of some grid points, given a stop aperture, there formed a grid image. The practical point image position of each field point deviated from their related chief ray position.  Thus the real grid image is different from the ideal image, which also shows the grid distortion. What is the different between case one and case two?  It seems case two is very direct to the grid distortion. Why zemax uses case two? What is the advantage? Thank you,

Mark.Nicholson · Accepted Answer

Hi,Distortion is the variation of magnification with field, and so it will depend on which field point you choose as the reference pointBy default we take the maginification seen by an on-axis parabasal chief ray as the reference point. This yields the curve above, in which the distortion is always a negative amount (in this case, which is the double Gauss sample). The red line is equivalent to making a mid-field point as the reference: now 75% of the distortion is positive with respect to that field point. Since changing distortion is non-linear, changing the reference field has an impact on the qualitative look of the result.Although distortion is easy to grasp as a concept, its execution is more involved. I’d recommend reading the Help file on the distortion feature closely, if you haven’t already.

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