I'm surprised by this outcome. I cropped the pictures so that they all showed the same area. It appears to me that the SX50 picture quality of a similarly distanced object is roughly the same as my 5D Mark III with 100-400 + Canon 2X teleconverter, and looks much better than my 7D with 100-400 + Canon 2X teleconverter.From what I can see, the images made with 7D & 5D MK III seem blurry ... I think this is most likely due to the IS issue as you mentioned (i.e. the IS not being able to sufficiently cope with the weight of the DSLR+big lens+2X tele-converter combo) ... it would be nice to see the same images made using a tripod.
I would have thought the 7D would have performed the best since it was shooting at a 1250mm equivalent, equal to the 1249mm equivalent of the SX50, but with presumably better picture quality.
Anyone have thoughts? The only thing I can think is that I was handholding all the cameras and maybe the SX50 has better IS than the IS on the 100-499?? And the SX50 is obviously a lot lighter and would be prone less to shake.
That being said, the SX50 seems to be a really handy tool in certain situations ... I just ordered the Nikon D7100 and a few other accessories (should be delivered tomorrow) ... will have to wait till I sell my current D7000 to buy this little beauty Canon SX50.
All three are blurry, because at such distances the light is traveling through a very blurry air mixture (a lot of it). No matter how stable your gear is, even if you use the best optics in the world, you are going to get this kind of blur anyway.