09-26-2017 01:32 PM
That depends on what you call "loose".
I checked my T6i (750D) and there is a millimetre of vertigal play. That is the part between a free button and the halfway mark. It isn't true play though as there is some feel in that short distance.
The halfway mark is the lock on your focus / exposure. Pressing the button to the halfway mark will lock the camera's exposure and where / what it is focused on. You may read the exposure values in the viewfinder or on the display. The focusing dots will light up on what the camera sees as the target.
This is an extremely important and valuable tool for composing your shot. If you are not on the object you want for a focus, release your finger and reapply until you get the correct object focused. If you dislike the Aperture or Shutter Speed, you can also adjust them before taking the picture. If you want your exposure for a certain object that isn't centered, then hold the button down halfway and move your camera to line up your shot.
If this isn't what you are calling loose, then I'm sorry I don't know. There isn't really any room on my cameras for any lateral movement.