Hi,

The reason you’re seeing such a big difference with the doublet between what you see in the Chromatic Focal Length analysis and the Layout is because the CFL uses paraxial rays and the layout as shown is real marginal rays.  For the Singlet, although there is also a difference between the paraxial and marginal focus, the difference is pretty consistent over the wavelength range so it appears that the CFL and Layout are in agreement (even though they are tracing different rays).  The differences becomes much more pronounced when using the difference dispersions of the Doublet to correct for color shift.

So the question of "which one is correct" really depends on what you’re trying to do, but in general, if you have a quantitative analysis like the CFL vs a qualitative analysis like visually looking at the Layout, I would recommend using the quantitative analysis as long as you understand the assumptions.

~Michael

Thanks micheal . I got it. the plano convex is actually a really flat lens where there is not much spherical abberation thus the overlap between paraxial to marginal rays is minimal whereas with the achromat there is significantly more spherical abberation thus there is a mismatch between marginal and paraxial rays. I confirmed this via reducing the entrance pupil diameter of the achromat where the rays traced are only paraxial and thus match the CFL tool