Hello,
As a new beginner to Zemax, I am not sure whether it is normal to get a negative stop radius in Prescription Data
below is part of my design result and in lens data the stop is a fixed R 5.75
my question is
Thank you !
Best answer by Jeff.Wilde
Actually, it seems like the sign of the stop radius is related to the sign of the paraxial magnification between the stop plane and entrance pupil. Here’s the same example, but this time the “Marginal and Chief Ray Only” option is selected in the layout window…
For negative entrance pupil magnification, a marginal ray coming from the top of the EP arrives at the bottom of the stop -- but in this case the marginal ray is propagating in the downward direction when viewed in the layout window.
Regards,
Jeff
+2Hi
Not a complete answer, but I can reproduce the negative Stop Radius by having two consecutive 4f systems where the center of the second 4f is the Stop Surface:
It could have to do with how the Stop Radius is calculated in the prescription report, if one takes the marginal ray that first goes upwards (positvie values of Y), it ends up having a negative Y intercept with the Stop Surface. I’ve tried to highlight this phenomenon in this figure:
Hence the negative Stop Radius reported. I think its only in the prescription report though, are you concerned about this value?
I hope this helps, and take care,
David
+3I think that’s a bug, although of a very minor kind. Since r=SQRT(x^2 + y^2) it should never have a sign. I suspect OS is reporting the y-value of the marginal ray height without taking the absolute part.
+3I find that the stop radius is positive when the stop is located at a paraxial collimating lens surface, but turns negative if the stop is moved slightly downstream…. Does look like some sort of minor bug.
Regards,
Jeff
+3Ooohhh, good call!
+3Actually, it seems like the sign of the stop radius is related to the sign of the paraxial magnification between the stop plane and entrance pupil. Here’s the same example, but this time the “Marginal and Chief Ray Only” option is selected in the layout window…
For negative entrance pupil magnification, a marginal ray coming from the top of the EP arrives at the bottom of the stop -- but in this case the marginal ray is propagating in the downward direction when viewed in the layout window.
Regards,
Jeff
Hi
Not a complete answer, but I can reproduce the negative Stop Radius by having two consecutive 4f systems where the center of the second 4f is the Stop Surface:
It could have to do with how the Stop Radius is calculated in the prescription report, if one takes the marginal ray that first goes upwards (positvie values of Y), it ends up having a negative Y intercept with the Stop Surface. I’ve tried to highlight this phenomenon in this figure:
Hence the negative Stop Radius reported. I think its only in the prescription report though, are you concerned about this value?
I hope this helps, and take care,
David
hi David
Thanks !
The highlight you showed is really understandable.
Best Regards!
Yang
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