There are two telescopes observing at night. The first telescope is 0.3m and has a focal ratio of f/8. The second telescope has a focal ratio of f/4 and is 30m in diameter. They each have an identical CCD camera whose pixels are 25 microns on a side. How much energy will be accumulated in a single pixel in a 100s exposure?
Note: Object being observed has an apparent brightness of 1.0*10^-7 W m^-2 and has an angular diameter of 15 arcsecsonds.
I have determined that the focal ratios of telescope 1= 2.4m and telescope 2 = 120m, and the the energy incident on one pixel:=(1.0*10^-7) 2.5*10^-5)^2(100s)= 6.25*10^-10.