Q:  Compute the number of photons in each bin integrated over
           the exposure (N), the uncertainty in that number (sig),
           and the percentage uncertainty (p = 100% * sig/N)


                  small telescope (D = 1m)       big telescope (D = 10m)

                          N      sig     p             N      sig     p
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  w = 100 Angstrom      6200      79    1.3        620,000    787    0.13

  w =  10 Angstrom       620      25    4           62,000    249    0.40

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