I’ve never used anything like

Forums Variable Stars Advice on variable star photometry setup I’ve never used anything like

James Screech

I’ve never used anything like 10 minute exposures, the longest I’ve used is 1 min, most of the time I use 10-20sec. 10sec will get me down to around mag 11 with errors about 0.03. I would only accept an error of 0.1 for secondary variables in the same field. Some fields I observe I can get photometry of 4 stars in the same field.

As for DSLR with my setup, a modified 500D with a 200mm f2.8 lens (about 70mm) I get good photometry to mag 8.3 with ISO400 and 20sec green channel only, unguided of an alt-az mount. I use a plan in APT that re-centres targets (with Goto++) about every 1 to 1.5 hours, as it does drift off centre without guiding on a low quality mount. 

Extrapolating isn’t easy as the magnitude will be a function of the camera pixel size, lens/telescope focal length and aperture.