>>3574417If you look carefully, the light cone to the left could be 100mm in height.
The light cone to the right could be 50mm in height.
This illustrates why the FF needs twice the focal length to get the same field of view.
But this also illustrates both holes must have exactly the same diameter to make it equivalent.
Hence if the FF system needs 25mm diameter hole, then so must the MTF system. Otherwise they won't gather the same amount of light.
