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Clarification on AXCL Computation and Chromatic Focal Shift in Zemax

Yujie

Hello Zemax Community,

I’m trying to understand the meaning of the numerical value displayed in “AXCL” and how it’s calculated. The definition I found states: “This is the image separation between the two wavelengths defined by Wave1 and Wave2,” but I’m still unsure how to interpret that in practice.

In my lens design, for example, the maximum focal shift is around 256.0465 µm, yet AXCL shows a value of -0.044014. I’m not sure what the negative sign means or why AXCL is so much smaller than the focal shift I see elsewhere. Is AXCL supposed to represent the chromatic focal shift, or is it defined differently? Any clarification on how AXCL is computed and what it physically represents in an optical system would be greatly appreciated!

Thank you in advance for your help and insights.
 

 

Best answer by Chandan.Maurya

Hi,

AXCL operand represent the focal shift from wavelength to wavelength. Since in your merit function you are seeing it for wave 1 and 3,  it is reporting focal shift for these two wavelengths only.

While focal shift plot shows the focal shift for full wavelength range and it will report maximum possible shift considering primary wavelength as reference (zero focal shift for Primary wavelength) instead wavelength to wavelength.

+ve and - ve values of AXCL represent the focal shift direction from reference focus.

SO, AXCL gives the focal shift from wavelength to wavelength whereas focal shift plot will give focal shift over entire wavelength range.

 

Thanks.

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  • Chandan.Maurya
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  • March 7, 2025

Hi,

AXCL operand represent the focal shift from wavelength to wavelength. Since in your merit function you are seeing it for wave 1 and 3,  it is reporting focal shift for these two wavelengths only.

While focal shift plot shows the focal shift for full wavelength range and it will report maximum possible shift considering primary wavelength as reference (zero focal shift for Primary wavelength) instead wavelength to wavelength.

+ve and - ve values of AXCL represent the focal shift direction from reference focus.

SO, AXCL gives the focal shift from wavelength to wavelength whereas focal shift plot will give focal shift over entire wavelength range.

 

Thanks.

David.Nguyen
Yujie
Rishab
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  • David.Nguyen
    David.Nguyen
  • Yujie
    Yujie
  • Rishab
    Rishab
Yujie
  • Yujie
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  • March 7, 2025

Thank you! I understand now. AXCL checks for a specific wavelength, but the focal shift is the actual value across the entire wavelength range.

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