If you want to fire the shutter with the mirror up to avoid mirror bounce, screw the cable release into the shutter release button on lens instead of the camera release button. Then turn the lens button so it's on manual. Then, once you compose the shot, you release the mirror manually with the big camera button you had been using. That will cause the mirror to lock up. Wait a few seconds for the tripod and camera to stop shaking, and then release the shutter with the cable release. I use this method all the time with my landscape shots.