I'm fairly new to astrophotography, and I began with a 450D, and immediately after moved to a 550D DSLR. I'm imaging M81-82 (with a zoom lens) and now I have half of the subs with one camera and half with the other one (I have calibration frames for each night).
It seems that deep sky stacker cannot stack them together because of the different size (12Mp for the 450D, 18Mp for the 550d). Is there a stacking software where I can do this? For example, does Siril allow me to do this? And if I have to upscale/downscale, which one of the two is better?