fix: thin lens pupil calculations - #375
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Reverse paraxial ray tracing (used for entrance pupil and front focal point/principal plane calculations) inverts each refraction step by negating the gap thickness and swapping n_0/n_1. For Conic and Sphere surfaces this swap also negates the surface's power for free, because their power formula (n_1 - n_0) / roc is antisymmetric in (n_0, n_1) — but ThinLens overrides power() to be media-independent (1 / focal_length regardless of arguments), so the swap had no effect and reverse traces used the wrong sign of power through any thin lens. This produced incorrect entrance pupil locations whenever a thin lens sat between the object and the aperture stop — e.g. the epifluorescence excitation path's entrance pupil was computed 31.58 mm after the first thin lens instead of 54.55 mm before it. surface_to_rtm now takes the reverse flag explicitly and negates the power directly when reversed, by calling power() with the original (un-swapped) n_0/n_1 ordering rather than relying on the formula's antisymmetry. This keeps Conic/Sphere behavior unchanged while fixing ThinLens. Adds the wf_epi_excitation example/test reproducing the reported system and asserting the hand-calculated entrance pupil location.
kmdouglass
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Reverse paraxial ray tracing (used for entrance pupil and front focal point/principal plane calculations) inverts each refraction step by negating the gap thickness and swapping n_0/n_1. For Conic and Sphere surfaces this swap also negates the surface's power for free, because their power formula (n_1 - n_0) / roc is antisymmetric in (n_0, n_1); but ThinLens overrides power() to be media-independent (1 / focal_length regardless of arguments), so the swap had no effect and reverse traces used the wrong sign of power through any thin lens.
This produced incorrect entrance pupil locations whenever a thin lens sat between the object and the aperture stop, e.g. the epifluorescence excitation path's entrance pupil was computed 31.58 mm after the first thin lens instead of 54.55 mm before it.
surface_to_rtm now takes the reverse flag explicitly and negates the power directly when reversed, by calling power() with the original (un-swapped) n_0/n_1 ordering rather than relying on the formula's antisymmetry. This keeps Conic/Sphere behavior unchanged while fixing ThinLens.
Adds the wf_epi_excitation example/test reproducing the reported system and asserting the hand-calculated entrance pupil location.