[frank]

I don't quite understand what the problem is here. Switch on a strong light bulb, shoot it with a wide-angle, then take your longest tele lens, shoot the light bulb from the same distance using the same f-stop and exposure time (!) and check which one comes out brighter. When aiming at a point light source, the telephoto will let much more light enter the system than a wide-angle, which is why shooting the mid-day sun with a telephoto is dangerous for your eyes. No?

Yes, it is true that at the same F-number and the same exposure time, the sensor collects more energy from the Sun for the tele lens. But the energy spreads over a larger area on the sensor. The energy received per unit area on the sensor is the same, providing that the incident angle of photons are the same.