I would like to buy a wide-aperture lens for an APS-C DSLR (Canon EOS 500D, crop factor 1.6x) with equivalent standard focal length. However, I was unable to decide between Sigma 30mm f/1.4 and Canon EF 35mm f/2 IS. The Canon is surely optically better, even has an image stabilizer and can be used on full-frame cameras if I decide to buy one in the future.
But I am mainly concerned with the background blur in terms of a rather wider portrait in exterior (forest, street), shot from 2 meters or a little less. The background blur is very similar in close-up images but I was unable to find a good comparison shot over longer distance (with deep background).
Would someone please be able to take two photos (at f/1.4 and f/2) similar to the portraits described with respect to the focal difference (so that the object in focus has the same magnification, what should be e.g. at 2 meters from 30mm and 2 1/3 for 35mm - potentially with a cropped photo from a 30mm lens)? I assume that with the 30mm lens, I could always step forwards and focus a bit closer to make the background more blurred. Unfortunately, I only own the EF-S 17-85mm f/4-5.6 whith which I can't simulate even crops from such wide-aperture lenses. I am totally aware that portraits are not a domain of such short focal length lenses but the reason I am buying one of there is that I am often limited by space. The possibility to shot nice portraits with it would come as an extra value to me.
As a side note for anyone knowing, how much necessary is the image stabilization in low-light conditions like indoor or even night photography?