I tried to understand the Ray Fan in OpticStudio and ran into this problem

I have a paraxial lens imaging an on-axis object (zero height) with 10 mm semi-diameter pupil size and focal length of 50 mm. Image plane is shifted 5 mm away from the focus intentionally, so it is at 105 mm from the lens. The Ray Fan plot is like this

Defocus term is the slope of this line and equals 0.05. Considering the defocus formula DF = focus shift x marginal ray height (10 mm) / focal length (50 mm) gives a 0.5 mm focus shift instead of 5 mm. I am not sure if I have problem with the definition of defocus term or with interpreting the Zemax data. Any idea?

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I think you have some simple errors in your analysis. If I understand your example case correctly, you have EPD = 10 mm (marginal ray height = EPD/2 = 5 mm), f = 50 mm, defocus = 5 mm. Please see the following version of your paraxial-lens model in which the ray fan results agree spot on with the analysis:

Can somebody help me to understand how to get the ray fan plot from the OPD plot?

In the case where i only have defocus and some piston as wave front errors, the first derivative of the OPD curve (polynomial of 2nd degree) should lead me to a linear function, describing the slope of the OPD at any pupil coordinate (independent of the piston, since it doesn`t change the slope of the OPD curve).

However, whenever i try to calculate the ray fan value at a certain pupil coordinate, it always deviates from the value thatis shown in the ray fan plot at that point. Why is that? Maybe i am making a thinking error.

My recipe would be as follows:

Read coordinates of max. pupil coordinate point of max. field in OPD plot. (both in mm for example)

calculate coefficient “a” of function OPD-value = a * pupil-coord. ^2 (since its a pure defocus)

Calculate derivative of quadratic OPD function (which gives me the linear ray fan function)

Calculate value of derivative of OPD function at max. pupil coordinate

→ should agree with value in ray fan plot at the same pupil coordinate