NSFCam2 Throughput Analysis
 
Filter     microns     Vega flux (W*m^-2*um^-1)     Bandpass     nu     E(J)     Photons*s^-1
J              1.250     3.01e-09                                       0.16     2.400e14     1.591e-19     2.140e10
H              1.644     1.18e-09                                       0.29     1.825e14     1.210e-19     1.999e10
K              2.198     4.00e-10                                       0.34     1.365e14     9.049e-20     1.062e10
L'              3.754     5.31e-11                                       0.70     7.991e13     5.049e-20     4.959e09
M'              4.702     2.22e-11                                       0.22     6.380e13     4.230e-20     8.161e08
 
Vega flux is from a model atmosphere, for an airmass=1 and 2mm of water nu: isophotal frequency E: energy per photon, h*nu mirror area = 7.06858 m^2 Photons*s^-1 = (flux*bandpass*area)/E
 
Filter     Star Mag     Observed count/s     mag=0.00 counts/s     e-/s         e-/photon     A
J              11.963       26650                     1.625e09                      6.500e09       0.303     0.440
H              11.703       37550                     1.802e09                      7.208e09       0.361     0.524
K              11.682       21783                     1.025e09                      4.100e09       0.386      0.561
L'                7.547     501600                     5.238e08                      2.095e09       0.422      0.613
M'                7.560       69470                     7.341e07                      2.936e08       0.360      0.523
 
 e-/s: counts/s * gain (gain=4)
 e-/photon = (e-/s)/(photons/s)
 transmission = 0.85*0.81 (mirror reflectivity^2 * filter transmission)
 A = (e-/photon)/transmission = instrument throughput * detector QE
 
   The throughput of the camera is between ~45% and ~60%.  The low sensitivity of the camera from J, H, and K is not due to a loss of photons, but must be due to the noise characteristics of camera.