Symptom: Colors different on left and right side

Sometimes the left side of an image has a (for example) red hue and the other side has more of a (for example) blue hue.

This effect doesn’t change if you turn the lens a little and also is unchanged if you turn the camera 180 degrees around its axis.

The cause for this is likely the microscopic structure of the pixels in combination with a lens with a CRA that is too large or a CRA that has correct size but has an F# that is too low.

Most sensors have an unsymmetrical pixel structure with the part that is sentitive to light being in a corner or on one side of the pixel:

(image : webfound)

As a photo it looks like this :
(image : webfound)

If the light arrives in allowed directions (the CRA is in tolerance), then all of the light will generally be directed to the light-sensitive part of the sensor pixel. An F# that is too low means that angles larger than the allowed CRA might occur , which can cause problems.

If the Angle of the arriving light is larger than allowed, then some light will arrive in the neighbour pixels (consisting of the light-sensitive part and of electronics to transport the charge).
Because the pixel structure is not symmetrical, light arriving from the left (for example) will arrive in the “blind spot” of the neighbor pixel, while light from the other side will arrive in the light sensitive part of the neighbor pixel.

The local asymmetry of the pixel structure leads to global asymmetry of the image colors!