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Question

Relative illumination at a given Y depends on field type

  • January 15, 2025
  • 1 reply
  • 27 views

mocquin

For a given system, with field type defined as “Real Image height”, the relative illumination at say Y=2mm is say 0.95

For the same system, with field type defined as “Paraxial Image Height”, the relative illumination at still Y=2mm is now 0.92.

Since the Y coordinates of the relative illumination curve are given in mm in the image plane, I would expect the relative illumanition value at a given height is independant of the field type selected.

What am I missing ?

 

1 reply

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  • Ultraviolet
  • 99 replies
  • January 16, 2025

Hi Mocquin,

You are comparing RI at two different positions:

  • When using Real Image Height, you are looking exactly at 2mm.
  • When using Paraxial Image Height, you are looking at the RI at a point probably close to 2mm, but it could be 1.95mm or 2.1mm (or something else, this is just an example). “Paraxial” is an approximation.

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