Spitzer IRAC photometry problems

If you have questions about the unit of IRAC photometry, you can check this website first:
http://coolwiki.ipac.caltech.edu/index.php/Units#Aside_on_fluxes_and_flux_densities
Also see https://irsasupport.ipac.caltech.edu/index.php?/Knowledgebase/Article/View/97/0/can-you-please-explain-how-the-irac-zmags-were-derived and the IRAC handbook
Need AB magnitude?  check upwebsite and read the following if you need more information:

(1) Explanation of AB magnitude and Vega magnitude
http://www.mattiavaccari.net/simstuff/simstuff05/node9.html
(2) Get the magnitude from IRAC image. obtain micro-Jy/pixel flux densities!
http://sohelp2.ipac.caltech.edu/support/index.php?/Knowledgebase/Article/View/30/8/how-do-i-convert-my-irac-images-into-flux-density-units-what-corrections-do-i-need-to-worry-about-how-do-i-convert-the-flux-densities-into-magnitudes


Last, here is the formula:

 The formula in the IRAC handbook is in Vega magnitude. Thus the zero points are different with different wavelength (Zeropoints can be found in Table 4.1 in the IRAC handbook). By the way, the unit in IR band is Jy.

 While I use the AB magnitude, the zero point is always 3631 Jy for all band (http://en.wikipedia.org/wiki/AB_magnitude).

 Thus one can use the following formula to get the AB magnitude:

    m_AB = -2.5*log10(f/3631 Jy)  

 For IRAC images which are in unit of  mJy/sr:

   m_AB 

   = -2.5*log10(f*1e6/(3361/8.461595  Jr/pixel) ) 

   = -2.5*log10(f)+ 21.581423