Here's how: 1  Stand with your feet shoulder-width apart and knees bent slightly. 2  Lean forward, placing your hands just above your knees. 3  Round your back so that your chest is closed and your shoulders are curved forward.  Then arch your back so that your chest opens and your shoulders roll 1  back. Repeat several times.
Typically this count is between 100,000 and 300,000 shutter actuations, with the latter limit associated with the EOS-1D models. In fact, the Camera Shutter Life Expectancy Database is a really neat user-based site for DSLR models of several brands, including Canon.
With ISO (International Standards Organization, previously known as ASA), we mean how quickly a film or digital sensor is capable of recording light. An image sensor set to ISO 100 requires twice as much light to achieve a normal exposure, as when the sensor is set to ISO 200. In order to get twice the light the shutter speed must either be doubled (e.g., from 1/60 to 1/30 seconds) or the aperture must be opened up a whole f-stop (e.g., from f/5.6 to f/4).