I own a crop sensor body and naturally have EF-S lenses because of my budget. I am extremely happy with my 55-250 EF-S lens, but it isn't that great for nature photography.
Now, I know that EF-S won't work on full frame, but full frame lenses work on a crop sensor body. Could I put a 2x extender on my 55-250mm and use that to get to 500mm on my camera? (I could technically afford a 70-300, but it doesn't have IS and I don't want a mostly-useless lens in my bag.)