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Hello Giovanni,
Thank you for your reply. Perhaps dismiss my “slow lens aperture” idea!
I have a Nikon D3200 camera, which has a CMOS sensor. With this camera I have performed some tests, for both JPEGs and NEF(RAW) images, and obtained the same “capacitor charging” curves.
I assume the sensor output is linear, so the “cause” must be the camera’s internal processing, programmed to suit general photography.
In fact, this non-linear camera output enables images to represent a greater tonal range, by compressing the higher brightness levels.
Possibly all “general photography” digital cameras work this way (?).
By comparison, your observation with the photoelectric cell seems much simpler, so I wish you good fortune with that project!
I’ve found this very interesting. Thank you for sharing your results!
Good wishes,
PeterHello again!
I’m not sure if you have yet resolved things to your satisfaction. Many of the suggestions seem very complicated, especially given that a stated advantage of CCDs, when they first appeared, was their linearity.
Another way of looking at your “curve” is that the shorter exposures are too bright.
Could it be that the lens aperture diaphragm is sticking or slow to close down?
In suggesting this, I don’t actually know if you are using the lens wide open or set to a smaller aperture.
It could be worth just trying a different lens.
Good wishes,
Peter LyonHello!
Have you got Nikon “Active D-Lighting” switched on, as your curve seems to show its effect, namely to boost the brightness gradient for low brightness levels, while stopping bright areas from reaching “fully white”?
If this is the problem, then switching off “Active D-Lighting” should solve the problem, and give a linear response.
Good wishes,
Peter Lyon
