The 220 HS has a fixed aperture with a variable aperture zoom. Hence, the only way to change the f-stop is by changing the zoom.
Yes, this is true of essentially all the ixus/sd line and A series (except some A series from before 2009 or so)
These cameras do have a neutral density (ND) filter. This can be used to reduce the amount of light reaching the sensor by several stops, and affects the aperture value recorded in the exif.
