I have just a limited budget and I wonder what lens I should buy.
There are currently two candidates:a) Peleng 8mm for my CAnon 40D or the b) Sigma 10-20mm .
I am using PTGUI for stitching. That should hopefully be no problem with these two lenses, right?
If somebody could help me with this decision it would really help.
PTGui will certainly handle both of your shortlisted lenses. You might also consider the new Samyang 8mm fullframe fisheye. I've only seen one panorama shot with this (by Michel Thoby at the second link below), but it looks promising. Flare performance may not be as good as the more expensive fisheyes, but then neither is that of the Peleng. See: