Does spatial resolution affect exposure at all?

Question

I have been testing two different sensors, using 3 lenses between each of the sensors. I have also kept the exposure to 6ms between each sensor. I noticed a difference in measured DN pixel values between targets for each respective sensor, at the same exposures.

The sensor with a lower spatial resolution has higher DN values of targets. And, the higher spatial resolution sensor consistently has lower values.

Does spatial resolution at all affect the exposure of an image, and thus the measured pixel values? As in, perhaps photons are more distributed amongst more pixels in higher spatial res. images, resulting in lower DN?

Answer 1

It all depends upon how one defines exposure. If one defines exposure as the total number of photons captured per pixel then pixel density will most definitely affect exposure.

But in photography exposure is normally expressed in terms of field density. That is, in terms of photons per area unit of the film or sensor's surface. When the raw sensor data is used to create a viewable image the number of photons measured per pixel is normalized to account for the varying sizes of pixel wells (more properly called sensels) in much the same way that the brightness of prints of various sizes from the same negative are normalized so that a print with twice the surface area of another print from the same negative does not wind up being half as bright.