The Sony Xperia Z doesn’t feature a physical camera button, and now black97one from the XDA developers has created a clever mode that lets you use the volume down button on your handset as a camera button, have a look at the video of it in action below.
Watch this video on YouTube.
You can find out full details on how to get this mod working on your Sony Xperia Z over at the XDA Developers. Your device will need to be on the latest firmware build (10.1.1A.1.307) and the leaked Android 4.2.2.
Source Xperia Blog