I am modelling a Phototopic eye system, which includes five wavelengths with different weights, in Zemax.
This system should have defocus of -0.5 diopter (D).
I want to know in a multi-wave system how the defocus is calculated?
Defocus is the average defocus of all five wavelengths?
Or
Defocus is the weighted average defocus of these five wavelengths (weighted based on the weight of the waves)?
Or
Defocus is calculated in a reference wavelength for example 555 nm?
Thanks.
Dear Elmira,
Assuming that you are working with a centered eye model, I suggest you look at the "Chromatic Shift" curve, and locate what wavelength has your expected defocus. Usually, the curve has a zero chromatic shift for the primary wavelength you have defined in ZEMAX, and, obviously, this can be changed.
However, I guess you are working with a complete, and realistic, model eye (non-centered). So, I suggest here that you use the expression corresponding to the equivalent defocus in terms of the Zernike defocus coefficient. This means that you have to calculate (take into account the pupil diameter ! ) the Zernike defocus for each wavelength, and check your expected result for defocus.
I hope this helps.
José Antonio
Hi Elmira,
I would assign the -0.5D defocus to a mid-spectral reference wavelength, say 550nm and then calculate the defocus at different wavelenths based on the chromatic shift José A. Díaz suggested above.
To put in my two pennies worth, there is an interesting nature paper by McLellan et al on the effect of chromatic blur in image quality and its (lack of) impact due to the eye's imperfect optics. See McLellan, J. S., Marcos, S., Prieto, P. M., & Burns, S. A. (2002). Imperfect optics may be the eye’s defence against chromatic blur. Nature. https://doi.org/10.1038/417174a
Dimitrios
Hello Elmira,
Defocus is usually defined with reference of image plane position.
I think it's better to calculate by the image surface position or center wavelength spot.
Mojtaba
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