I am a regular user of VPHOT now with SDSS filters. However I have found that the signal to noise ratio of stars are quite different from those supplied for the same stars by other softwares such as Maxim DL or Aip4win. I have used the same aperture, gap and sky annulus. Maxim DL delivers much higher SNR compared to VPHOT while Aip4Win delivers results more in line with VPHOT. Just out of curiosity I wonder why I obtain different results.
Do you use also the exact same photo ?
I have to 2x2bin before sending to VPHOT and therefore the SNR is way worse in VPHOT than in other softwares where I use the original calibrated photo.