There are several things affecting the variability between sensors
because the sensor "system" is three-dimensional object, not a
two-dimensional flat plane:
1. Microlenses. On nearly all sensors, the microlenses offset the
farther away from center they get. This keeps the angled light coming
from the lens from vignetting as much. However, the placement of these
microlenses is dependent upon the camera manufacturers lenses as it is
part of the goal to match the brand's lenses to the brand's cameras as
much as possible. This is why RF lenses don't do as well on some
sensors because the microlenses aren't shifted enough.
2. Filter stack. There are generally three layers involved: UV, IR and
AA. Depending on the manufacturer and generation, there is a fourth
layer--a wave plate.
3. The sensor itself. Depending on the manufacturer and generation of
sensor, there is a "well depth" involved with results in attenuation
of signal with light coming in at steep angle into the sensel.
So, when you use a lens with a large exit pupil on the camera, you can
end up with a wide range of angle of incidence, instead of a very
narrow range from a stopped down lens. The microlenses are optimized
for a midrange f-stop where the light can be redirected mostly to the
underlying sensel without too much scattering. But with a wide-open
lens, with large exit pupil that is placed close to the sensor, there
is significant scattering.
This is why some manufacturers implemented wave plate or equivalent
technologies instead of or in addition to the microlenses. There
were/are High-end medium-format sensors that not only lack AA filters,
but microlenses as well. Instead of microlenses, they use wave plate
type technology for light alignment into the sensel.
The key here is that these are all spices available to the designers.
No to brands or even models use the same recipe. As a result, there
will be specific lens/sensor combinations that will be magical and
others that are mush.
AG Schnozz
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