Computation of Seidel coefficients

[malekmok]

Hi all,

I've started running some initial tests using Optiland.

In my first test, I encountered an issue related to the computation of third-order aberrations. I'm sharing here a simple example involving a singlet lens :
#======================== CODE ==================
import numpy as np
from optiland import optic, materials

singlet = optic.Optic()
thic = 13.81
radius = 224.69890346935105
EPD = 80
silica = materials.IdealMaterial(n=1.458)

add surfaces

singlet.add_surface(index=0, thickness=np.inf)
singlet.add_surface(index=1,
thickness = thic,
radius=radius,
is_stop=True,
material= silica)

singlet.add_surface(index=2, thickness=222)
singlet.add_surface(index=3)
singlet.set_aperture(aperture_type="EPD", value=EPD)

add field

singlet.set_field_type(field_type="angle")
singlet.add_field(y=0)

add wavelength

singlet.add_wavelength(value=0.601, is_primary=True)
singlet.image_solve()
singlet.draw(num_rays=11)
singlet.info()

print("Seidel Aberrations:")
for k, seidel in enumerate(singlet.aberrations.seidels()):
print(f"\tS{k + 1}: {seidel:.3e}")

print("Third-order transverse spherical aberration:")
for k, value in enumerate(singlet.aberrations.TSC()):
print(f"\tSurface {k + 1}: {value:.3e}")

print("Third-order longitudinal spherical aberration:")
for k, value in enumerate(singlet.aberrations.SC()):
print(f"\tSurface {k + 1}: {value:.3e}")

#======================== END OF CODE ==================

With Optiland, all the returned coefficients are zero!

With Zemax, I obtain : S1 = 0.059 and W040=12.45 wave.

It’s possible that I missed something while using Optiland. Could you help me obtain results similar to those from Zemax?

Thank you in advance for your help.

my_singlet.zip

[HarrisonKramer]

Hi @malekmok,

Thanks for opening this! I confirmed that I get the same behavior.

I can see that the issue arises when there is only a single on-axis field. As a workaround, you can add a small field:

singlet.add_field(y=1e-10)

Then, you will recover the expected spherical aberration (although I see -0.059 instead of +0.059). This appears to be a bug. I will open an issue to track this. I expect it's a relatively simple fix.

Thanks again!
Kramer