Originally posted by tuco I'm not an expert but I think you've been shooting digital too long.
Well, I'm sort of an expert, as optical design is my job... We probably just don't understand each other fully.
I'll repeat my statement differently :
if more light falls on one individual pixel, then you improve the signal to noise ratio of your measurement. In short, your high ISO performances will be better for the same level of technology.
To get more light on one pixel, you can either let more light through the lens, or make the pixel larger.
Making the pixel larger while preserving the resolution yields a larger sensor. Fair game.
Keeping the pixel size while increasing the sensor size will increase your pixel count (resolution) but will not improve the performance of individual pixel. The light intensity
per surface element will be the same as before.
So increasing the sensor size does not, necessarily, improve the light gathering performances. The total amount of light hitting the sensor increases, true, but that does not necessarily relate to better noise figures.
And you have to take into account that a larger sensor also generates more heat, so all things being equal it will perform more poorly than a smaller sensor (I grant you that between APS-C and FF, the difference in heat will not be dramatic).
I hope my meaning is clearer.