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Settings > apps > all > camera > clear data > restart your Xperia S > check again
You can also boot on safe mode and check if you encounter the same issue
http://talk.sonymobile.com/t5/FAQ/How-to-boot-your-phone-into-safe-mode/m-p/348008#U348008
If you don't then its an app acting up
Check the above link
The next step will be for you to backup your phone then repair your phone with PCC
Bridge (for Mac)
Alternatives on How to backup Xperias
http://talk.sonymobile.com/thread/36355
keep us updated after you repair your phone with PCC