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Question

Does the GENF operand include or exclude rays vignetted before the image plane?

  • February 12, 2025
  • 1 reply
  • 42 views
Ryan.Burdick

When using the geometric encircled energy (fraction) operand, GENF, does the fractional energy calculation include rays that are vignetted by elements before the image plane in the total energy part of the calculation?

For example, suppose 100 rays are launched from the object. 5 rays are blocked by some aperture in the middle of the optical system. At the image plane, 90 rays land within the radius set by GENF. 5 rays made it to the image plane, but they landed outside of the radius set by GENF.

Is the fractional energy returned by GENF 90/100 = 90%? Or is the fractional energy 90/95 = 94.7%?

    Jeff.Wilde
    Luminary
    Forum|alt.badge.img+3

    ​@Ryan.Burdick:

    A simple test model indicates that the geometric encircled energy is normalized by the energy associated with only those rays actually hitting the surface of interest.  So, the answer to your question seems to be 90/95 = 94.7%.

    Here is the test model:

     

    Even though rays are blocked by an aperture on Surface 2, the encircled energy still reaches 100% behind the aperture.  In this case the  “Multiply by Diffraction Limit” option was turned off because this isn’t an imaging model.  

    Regards,

    Jeff

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