I have a Canon 700D and I am new to photography (around 1 month). I got two kit lenses with my camera - the 18-55mm and 55-250mm. I usually use the 18-55mm lens as most of photography I have yet done has been indoors. I also heard somewhere that this lens is good for portraits and the other is a telephoto lens which is good for comparatively distant shots.
Yesterday I was clicking friends' pictures on our roof, but the background-blur effect was not quite clear. Just to check, I changed the lens to the 55-250mm and it was really good at creating blurred backgrounds with sharply focused objects (my friends). Should I use this lens for shooting portraits then?
I know some theoretic basics about Depth of Field and that aperture should be wider to create shallower DOF, but what I am not able to understand is that for same settings(Automatic modes - portrait mode), shouldn't the 18-55mm lens also create the same effect? It looks like that lens does not increase its aperture as nicely as the other lens does.