Thu 11-Oct-12 05:53 AM | edited Thu 11-Oct-12 05:56 AM by PerroneFord
>Haha, brain gymnastics
>However, if you an FX camera with a lens optimized for that >sensor,
I assume you to mean an FX lens placed on an FX camera..
>and compare that to a DX camera with a DX optimized >lens,
With you so far...
>then the light of the lens will be spread over a larger >area on rhe FX camera, giving you less photons per pixel.
Also incorrect. You are assuming that the light emitted by the two lenses is equal. In fact they are not. The exit pupil of the FX lens is necessarily larger giving that lens more light transmissivity.
So in fact what is happening is that the FX lens is offering more light to begin with, than the DX lens. And when spread over a larger area, it offers a similar amount of light per square area to the FX sensor. Were this not true, then an F2.8 lens would HAVE to meter differently on the two systems. But since the amount of light is equalized over the two systems, the rest of the mathematics holds true, giving us the same light gathering at the same F-stops.