I have released a new version of the ASTAP program (2025.12.28). The photometry tab has been fully adapted for Sloan filters SG, SR, SI and the new local database (seperate download) contains the Sloan magnitudes from ATLAS-REFCAT2 down to magnitude 15.
Observing variable stars with Sloan filters is a niche/rare and will not replace Johnson-Cousins filters but at least you experiment with it if you have the filters.
Measuring the transformation coefficients of your Sloan filters is possible, but I assume that doesn’t help much since most filters will be very close to the Sloan standard and then transformation doesn’t help. For example in screenshot below Tg_gr and Tr_gr are very low.
Are you referring to the new “Variables” database on your download page? Do I still need another database like V05/V50 or is that included in “Variables” database?
For Sloan photmetry you will need a newer local variable database (Selection AAVSO annotation: Local DB ….). This variable database contains beside the variables all comparison & standard field stars with the magnitudes for B, V, R, SG, SR, SI. Currently in the online AAVSO annotation database for only a tiny fraction of comparison stars are Sloan magnitudes available. If you do not update the local variable database the program will complain if you try to process Sloan images. Download newest variable star database from here:
The Gaia comp. stars selection you best set on “Online database” rather then the V50. See the red marked section in the screenshot below. Then the program will convert Gaia magnitudes to Sloan magnitudes making the instrumental magnitude reasonable correct. The final correction is done with the selected comparison stars
(Note that the most convenient way of operation is “Measure all annotated” and select your stars in the report.)
The map will show only the magnitudes according the filter (new). The screenshot below is a part of M67 showing the SR magnitudes of the standard stars:
