Having recently spent some time fighting for light with a high-speed camera having a CS mount and a sensor area under .1 inches2, I was wondering if the f rules apply to cropped sensors?
For example: A full-frame lens is designed to focus an image on a 1.3 square-inch sensor. Suppose I run a full-frame lens at f/2. I can just project that on the crop sensor, which will give me the same amount of light as if I ran a CS lens of identical construction at f/2. But given that we have a fully-resolved image at the full-frame sensor plane, can't we project it onto the crop sensor, thereby producing an f/2 depth of field that's roughly 13 times as bright as what we get from an f/2 CS-mount lens?