Galaxies:

Standard deviations in magnitudes for galaxy photometry vs. log (S/N), surface 
brightness, and magnitude.

Exponential functions reported by DataGraph for the following plots:

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Galaxies:  y = sigma1 vs x [x = log (S/N), U magnitudes]
  Fit:  y = 0.01981*exp((-1.093)*x))

Galaxies:  y = sigma1 vs x [x = log (S/N), B magnitudes]
  Fit:  y = 0.019948*exp((-1.068)*x)

Galaxies:  y = sigma1 vs x [x = log (S/N), V magnitudes]
  Fit:  y = 0.015138*exp((-1.2712)*x)

Galaxies:  y = sigma1 vs x [x = log (S/N), R magnitudes]
  Fit:  y = 0.018641*exp((-1.205)*x)

Galaxies:  y = sigma1 vs x [x = log (S/N), I magnitudes]
  Fit:  y = 0.02123*exp((-1.1703)*x)
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Galaxies:  y = sigma1 vs x [x = surface brightness, U magnitudes]
  Fit:  y = 0.00019173*exp(0.38192*x)

Galaxies:  y = sigma1 vs x [x = surface brightness, B magnitudes]
  Fit:  y = 0.00016291*exp(0.37079*x)

Galaxies:  y = sigma1 vs x [x = surface brightness, V magnitudes]
  Fit:  y = 6.1077e-5*exp(0.45415*x)

Galaxies:  y = sigma1 vs x [x = surface brightness, R magnitudes]
  Fit:  y = 8.8849e-5*exp(0.45919*x))

Galaxies:  y = sigma1 vs x [x = surface brightness, I magnitudes]
  Fit:  y = 0.00020981*exp(0.43855*x)
-----
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Galaxies:  y = sigma1 vs x [x = U magnitudes]
  Fit:  y = 7.1828e-5*exp(0.51175*x) 

Galaxies:  y = sigma1 vs x [x = B magnitudes]
  Fit:  y = 0.00014873*exp(0.42978*x)

Galaxies:  y = sigma1 vs x [x = V magnitudes]
  Fit:  y = 0.00023764*exp(0.40571*x)

Galaxies:  y = sigma1 vs x [x = R magnitudes]
  Fit:  y = 0.00024288*exp(0.44386*x)

Galaxies:  y = sigma1 vs x [x = I magnitudes]
  Fit:  y = 0.00065005*exp(0.40626*x)
-----

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Standard deviations in magnitudes for photometry of stars vs. magnitude.

Exponential functions reported by DataGraph for the following plots:

Stars:  y = sigma1 vs x [x = U magnitudes]
  Fit:  y = 0.00019743*exp(0.38561*x)

Stars:  y = sigma1 vs x [x = B magnitudes]
  Fit:  y = 0.00022603*exp(0.33567*x)

Stars:  y = sigma1 vs x [x = V magnitudes]
  Fit:  y = 0.00096361*exp(0.22642*x)

Stars:  y = sigma1 vs x [x = R magnitudes]
  Fit:  y = 0.0013011*exp(0.22603*x)

Stars:  y = sigma1 vs x [x = I magnitudes]
  Fit:  y = 0.00078601*exp(0.30893*x)