Formulas that Vphot uses ?

Hi,

As I managed to get Vphot running, I was tempted to do some comparaisons between AstroImageJ and Vphot. 
I used the same "sequence", and the same photo's. When I verify the pixelcounts (peak) I get exactly the same results. So, that is good. 

Comparing magnitudes gives the same result too (plus/minus), but when comparing the error estimates, there is quite some difference. Also SNR is quite different. Vphot giving much more "optimistic" values. 

In annex a print of a comparison of the V0830Cep star, one that is getting near the boundary of my observing possibilites, thus more prone to a larger measuring error. 

With AstroImageJ there is a good paper about all the formulas they are using. When redoing their calculations in excel with their formulas one finds quite easily the same values.

As the difference is quite impressive, I am wondering if there is such document for VPhot also ? 


Pieter.